Dry skin is one of the most common dermatological complaints, and while environmental factors and skincare habits play a role, persistent dry skin that doesn’t respond to topical treatment often signals an underlying condition. Your skin is your body’s largest organ, and its condition reflects what’s happening inside.

The skin requires adequate hydration, proper oil production, normal cell turnover, and sufficient nutrients to maintain its barrier function and stay supple. When internal systems are disrupted — thyroid function, blood sugar regulation, hormone levels, or nutritional status — the skin is often one of the first places to show it.

Understanding what’s causing your dry skin from the inside can transform your approach from endless moisturizing to actually addressing the root cause. Blood testing can identify many of the internal factors that contribute to chronically dry skin.

Understanding Skin Hydration

To understand why skin becomes dry, it helps to understand how healthy skin maintains its moisture. Skin hydration is a complex process involving multiple layers, proteins, lipids, and active mechanisms that work together to keep skin soft, supple, and protected.

The skin barrier:

The outermost layer of skin — the stratum corneum — acts as a barrier between your body and the environment. Think of it as a brick wall:

• Corneocytes (the “bricks”): Flat, dead skin cells stacked in organized layers, typically 15-20 cells thick. These cells are filled with keratin proteins that provide structural strength.
• Lipid matrix (the “mortar”): A complex mixture of ceramides (about 50%), cholesterol (about 25%), and free fatty acids (about 15%) that fills the spaces between cells. This lipid matrix is crucial — it prevents water from escaping and keeps irritants from entering.
• Natural moisturizing factors (NMF): Hygroscopic (water-attracting) substances within the corneocytes that draw water from the environment and hold it within the cells. NMF includes amino acids, urea, lactate, and other compounds.

When this barrier is intact and functioning properly, it prevents excessive transepidermal water loss (TEWL) — the constant evaporation of water through the skin that happens even in healthy skin. In healthy skin, TEWL is minimal. When the barrier is compromised, TEWL increases dramatically, and the skin becomes dry regardless of how much water you drink.

What the skin needs to stay hydrated:

• Adequate sebum production: Sebaceous glands produce sebum, an oily substance that spreads over the skin surface and helps seal moisture in. Sebum contains triglycerides, wax esters, squalene, and free fatty acids. Too little sebum leads to dryness; this is why areas without sebaceous glands (like the shins) are prone to dryness.
• Normal cell turnover: Skin cells are constantly being produced in the basal layer, moving upward, dying, and eventually shedding from the surface. This process takes about 4 weeks in healthy skin. Abnormal turnover can cause buildup of dead cells (leading to flakiness) or insufficient barrier formation (leading to increased water loss).
• Proper lipid production: The ceramides, cholesterol, and fatty acids in the skin barrier require adequate raw materials — including essential fatty acids from the diet — and proper enzymatic machinery to produce.
• Adequate hydration: Overall body hydration affects skin hydration, though less directly than people often assume. Severe dehydration definitely affects skin, but drinking extra water when already adequately hydrated doesn’t significantly improve skin moisture.
• Hormonal regulation: Hormones, particularly thyroid hormones, androgens, and estrogens, regulate sebum production, skin cell turnover rate, and skin thickness. Hormonal imbalances commonly manifest as skin changes.
• Nutrient availability: Various vitamins and minerals are essential for skin health and barrier function — vitamin A for cell differentiation, vitamin D for barrier function, zinc for wound healing and skin structure, essential fatty acids for lipid production.
• Normal nerve and blood vessel function: Nerves regulate sebum production and blood flow; blood vessels deliver nutrients and oxygen. Conditions affecting nerves or circulation affect skin health.

Types of dry skin:

Xerosis: The medical term for dry skin. Can range from mild roughness and flakiness to severe cracking and fissuring. Most common on shins, forearms, and hands. Severity increases with age.

Ichthyosis: A group of conditions causing severe, scaly dry skin with a fish-scale appearance. Usually genetic (ichthyosis vulgaris is most common) but can be acquired in association with cancer, HIV, hypothyroidism, or medication use. More severe than simple xerosis.

Eczema (atopic dermatitis): An inflammatory skin condition characterized by dry, itchy, inflamed patches. Has a strong genetic component and is associated with immune dysregulation. The skin barrier is inherently defective in eczema, with reduced ceramide content.

Asteatotic eczema (eczema craquelé): Extremely dry skin with a characteristic cracked, “crazy paving” appearance, like cracked porcelain. Most common on the shins of older adults. Often triggered by over-bathing, low humidity, or systemic illness.

When Dry Skin Suggests an Internal Cause

Not all dry skin indicates a medical problem. Environmental factors — cold weather, low humidity, hot showers, harsh soaps, natural aging — commonly cause dry skin and respond well to external remedies like moisturizers and humidifiers. However, certain patterns suggest something internal is going on that requires investigation and treatment beyond skincare.

Dry skin from external causes typically:

• Worsens in winter (when humidity is low) and improves in summer
• Responds well to moisturizer, humidifier use, and avoiding hot water
• Affects exposed areas (hands, face) more than covered areas
• Improves with changes in skincare routine (gentler soaps, better moisturizers)
• Doesn’t have associated systemic symptoms (you feel fine otherwise)
• Has been present lifelong or correlates with known environmental changes

Dry skin suggesting an internal cause:

• Persists despite good skincare practices and adequate environmental humidity — you’re doing everything right but it’s not helping
• Represents a change from your previous skin — you didn’t used to have dry skin, or it’s gotten noticeably worse
• Is accompanied by other symptoms (fatigue, weight changes, hair changes, feeling cold, increased thirst, frequent urination)
• Affects the whole body uniformly, including areas not exposed to the environment
• Doesn’t respond meaningfully to typical moisturizing strategies
• Is severe — cracking, fissuring, bleeding, painful
• Started around the same time as other health changes or new symptoms
• Is accompanied by changes in hair (dry, brittle, falling out) or nails (brittle, ridged, spoon-shaped)
• Is progressive — getting worse over time despite your best efforts
• Has a characteristic pattern (yellowish tinge, cool to touch, puffy appearance) that suggests a specific condition

Associated symptoms that provide diagnostic clues:

When dry skin occurs alongside other symptoms, the pattern often points toward specific causes:

• Dry skin + fatigue + feeling cold + weight gain + constipation: Strongly suggests hypothyroidism — this is the classic pattern
• Dry skin + excessive thirst + frequent urination + blurred vision: Suggests diabetes
• Dry skin + hair loss + brittle nails: Suggests nutritional deficiency (especially iron or biotin) or thyroid dysfunction
• Dry skin + fatigue + pale skin + shortness of breath: Suggests anemia, likely iron deficiency
• Dry skin + digestive symptoms (diarrhea, bloating): Suggests malabsorption (celiac disease, inflammatory bowel disease, pancreatic insufficiency)
• Dry skin + itching + swelling + changes in urination: Suggests kidney disease
• Dry skin + hot flashes + irregular periods: Suggests menopausal transition
• Dry skin + jaundice + abdominal symptoms: Suggests liver disease

The more associated symptoms you have, the more likely an internal cause is at play. But even isolated dry skin that doesn’t respond to external measures warrants consideration of internal causes.

Hypothyroidism: The Classic Internal Cause

If there’s one condition most classically associated with dry skin, it’s hypothyroidism. Dry, rough, pale skin is so characteristic of an underactive thyroid that it’s listed as one of the classic textbook signs — and it’s often one of the first symptoms people notice. Studies suggest that skin changes occur in 50-80% of people with hypothyroidism, making it one of the most reliable external indicators of thyroid dysfunction.

How thyroid affects the skin:

Thyroid hormones regulate metabolic rate throughout every tissue in the body, including the skin. The skin has receptors for thyroid hormones, and these hormones directly influence multiple aspects of skin function. When thyroid function is low:

• Reduced sebum production: Thyroid hormones stimulate sebaceous glands to produce sebum. With low thyroid, sebum production can decrease by 50% or more, dramatically reducing the skin’s natural oil coating that seals in moisture.
• Decreased sweating: Thyroid hormones affect sweat gland activity. People with hypothyroidism sweat less, contributing to skin dryness and explaining their cold intolerance.
• Impaired skin cell turnover: The normal cycle of skin cell production, maturation, and shedding slows down dramatically. Cells take longer to move from the basal layer to the surface and longer to shed, leading to accumulation of dead cells (flakiness) and impaired barrier function.
• Reduced blood flow to skin: Hypothyroidism decreases peripheral circulation as part of the metabolic slowdown, reducing nutrient and oxygen delivery to the skin and impairing its function.
• Changes in skin composition: Mucopolysaccharides (glycosaminoglycans) can accumulate in the dermis, causing a puffy appearance (myxedema) while paradoxically leaving the surface dry due to barrier impairment.
• Impaired wound healing: Skin repairs more slowly due to the overall metabolic slowdown. Cuts and scrapes take noticeably longer to heal.
• Carotenemia: Impaired conversion of beta-carotene to vitamin A causes carotene to accumulate, giving skin a yellowish-orange tinge, especially on palms and soles.

Characteristics of thyroid-related dry skin:

• Generalized dryness affecting the whole body, not just exposed areas
• Rough, coarse texture — sometimes described as “sandpaper-like”
• Pale or yellowish tinge (carotenemia from impaired carotene conversion)
• Cool to touch due to reduced blood flow
• Slow wound healing — cuts and scrapes take noticeably longer
• May have a puffy, doughy appearance, especially on face, hands, and feet
• Particularly severe on shins, elbows, and knees — areas with fewer sebaceous glands
• Developed gradually over months or years — so gradual you may not notice until seeing old photos
• Doesn’t respond well to moisturizers alone

Other hypothyroidism symptoms typically present:

• Fatigue and low energy — often profound, not relieved by sleep
• Feeling cold when others are comfortable
• Unexplained weight gain despite unchanged eating habits
• Constipation
• Dry, brittle hair and hair loss (including thinning of outer eyebrows)
• Brittle, ridged nails
• Brain fog and difficulty concentrating
• Depression or low mood
• Muscle weakness, aches, and cramps
• Slow heart rate (bradycardia)
• Puffy face, especially around eyes
• Hoarse or deeper voice
• Heavy or irregular menstrual periods

The combination of dry skin with fatigue, cold intolerance, and weight gain is highly suggestive of hypothyroidism. If you have several of these symptoms together, thyroid testing is essential.

Hashimoto’s thyroiditis:

Hashimoto’s thyroiditis — the autoimmune cause of most hypothyroidism in developed countries — typically develops slowly over months to years. The immune system gradually destroys thyroid tissue, and function declines proportionally. Skin changes may be so gradual that you don’t notice until someone points out that your skin looks different, or until you compare yourself to old photos. The slow onset means people often attribute their dry skin to aging or weather rather than recognizing it as a symptom.

What to test:

TSH is the primary screening test. Elevated TSH indicates the thyroid is underperforming — the pituitary is producing extra TSH to try to stimulate more hormone production.

Free T4 measures the main circulating thyroid hormone. Low free T4 with elevated TSH confirms hypothyroidism.

Free T3 measures the active thyroid hormone. Some people have adequate T4 but poor conversion to T3, causing symptoms even when T4 looks acceptable.

TPO antibodies identify Hashimoto’s thyroiditis, the autoimmune cause of hypothyroidism, explaining why thyroid function is declining.

Diabetes and Skin Health

Diabetes affects the skin through multiple mechanisms, and dry skin is one of the most common dermatological manifestations of this metabolic disorder. An estimated 30-70% of people with diabetes have some form of skin involvement, and dry skin is often among the earliest signs — sometimes appearing before diabetes is formally diagnosed.

Skin changes in diabetes are so common and characteristic that dermatologists sometimes suspect diabetes based on skin examination alone, prompting the blood tests that confirm the diagnosis. If you have unexplained dry skin along with risk factors for diabetes (overweight, family history, sedentary lifestyle), blood sugar testing is particularly important.

How diabetes causes dry skin:

• Dehydration from high blood sugar: When blood glucose is chronically elevated, the kidneys work overtime to excrete the excess glucose in urine. This glucose acts as an osmotic diuretic, pulling water with it. The result is increased urination (polyuria) and overall body dehydration, which directly affects skin hydration. This is why increased thirst (polydipsia) accompanies high blood sugar — the body is trying to replace lost fluid.
• Reduced sweating (anhidrosis): Diabetic autonomic neuropathy — damage to the nerves that control involuntary functions — can affect sweat glands. Reduced or absent sweating contributes significantly to skin dryness and also increases risk of overheating.
• Poor circulation: Diabetes damages blood vessels over time through multiple mechanisms (endothelial dysfunction, accelerated atherosclerosis, microvascular damage). Reduced blood flow means the skin receives less oxygen and fewer nutrients, impairing its function and ability to maintain hydration.
• Nerve damage affecting skin function: Diabetic neuropathy affects not just sensation but also the nerves that control skin oil production and blood vessel dilation. This disrupts the skin’s natural hydration and temperature-regulation mechanisms.
• Impaired skin barrier: Chronically elevated blood sugar affects the proteins and lipids that maintain the skin barrier, increasing transepidermal water loss. High glucose can also glycate (chemically modify) skin proteins, altering their function.
• Increased susceptibility to infections: Dry, cracked skin provides entry points for bacteria and fungi. Combined with the impaired immune function that accompanies diabetes, this makes diabetic skin prone to infections — which can further damage skin integrity.
• Impaired wound healing: Diabetes impairs every phase of wound healing. Even minor cuts, scrapes, and cracks heal slowly, and these wounds can become chronic, especially on the feet.

Characteristics of diabetes-related dry skin:

• Often most pronounced on lower legs and feet — these areas are furthest from the heart and most affected by poor circulation and neuropathy
• May be accompanied by itching (pruritus) — a common complaint in diabetes
• Slow wound healing — minor cuts and scrapes take noticeably longer to heal than they should
• Cracked heels and very dry feet — sometimes with deep, painful fissures
• May have other characteristic diabetic skin changes:
  • Acanthosis nigricans: Dark, velvety patches in skin folds (neck, armpits, groin) — a marker of insulin resistance
  • Diabetic dermopathy: Light brown, scaly patches on the shins (“shin spots”)
  • Skin tags: Multiple skin tags, especially in skin folds
  • Yellow skin: Waxy, yellow appearance from glycation of skin proteins
• History of frequent skin infections — bacterial or fungal

Other diabetes symptoms often present:

• Increased thirst (polydipsia)
• Frequent urination (polyuria)
• Unexplained weight loss (more common in type 1, can occur in uncontrolled type 2)
• Fatigue and low energy
• Blurred vision
• Slow-healing wounds
• Frequent infections (urinary, skin, vaginal yeast)
• Numbness or tingling in hands or feet (peripheral neuropathy)

Prediabetes and skin:

Prediabetes — when blood sugar is elevated but not yet in the diabetic range — can also affect the skin. Acanthosis nigricans (dark, velvety skin patches, especially in body folds like the neck and armpits) is particularly associated with insulin resistance and often appears years before diabetes is formally diagnosed. If you have acanthosis nigricans, blood sugar testing is strongly recommended.

What to test:

Fasting glucose screens for elevated blood sugar. A single elevated fasting glucose may indicate diabetes or prediabetes.

HbA1c (glycated hemoglobin) reflects average blood sugar over the past 2-3 months. It can diagnose both diabetes and prediabetes and doesn’t require fasting.

Fasting insulin can detect insulin resistance — the underlying metabolic dysfunction — before glucose becomes significantly abnormal. Elevated fasting insulin with normal glucose suggests insulin resistance, which can cause skin changes (like acanthosis nigricans) even before you meet criteria for prediabetes.

Nutritional Deficiencies

The skin requires various nutrients to maintain its structure, function, and hydration. The skin is a metabolically active organ that depends on a steady supply of vitamins, minerals, fatty acids, and proteins. Deficiencies in key nutrients commonly manifest as dry, rough, or scaly skin — and the skin is often one of the first places where nutritional problems become visible.

Essential Fatty Acid Deficiency:

Essential fatty acids (omega-3 and omega-6) are critical components of skin cell membranes and the lipid matrix that forms the skin barrier. They cannot be synthesized by the body and must come from the diet. Deficiency causes:

• Dry, scaly skin throughout the body
• Rough, bumpy skin texture (similar to keratosis pilaris)
• Significantly increased transepidermal water loss — the skin can’t hold moisture
• Dermatitis — red, inflamed patches
• Poor wound healing

True essential fatty acid deficiency is rare in developed countries with normal diets but can occur with very low-fat diets (extreme fat restriction), malabsorption conditions (celiac disease, Crohn’s disease, chronic pancreatitis), cystic fibrosis, or prolonged IV nutrition without lipid supplementation. The skin changes are among the first signs of deficiency.

Vitamin A:

Vitamin A is essential for skin cell differentiation, maintenance, and repair. It regulates how skin cells develop and mature. Deficiency causes characteristic skin changes:

• Dry, rough, scaly skin — xerosis is an early sign
• Follicular hyperkeratosis — rough, raised bumps around hair follicles, especially on the back of arms and thighs, giving a “goose bump” or “toad skin” texture
• Night blindness (often the first noticeable sign)
• Dry eyes (xerophthalmia)
• Increased susceptibility to infections

Vitamin A deficiency is rare in developed countries with adequate nutrition but can occur with severe malabsorption (celiac disease, Crohn’s disease, pancreatic insufficiency), very restrictive diets (extremely low-fat vegan diets without supplementation), chronic liver disease (the liver stores vitamin A), or alcoholism.

Vitamin D:

Vitamin D plays important roles in skin barrier function, skin cell growth and differentiation, wound healing, and immune regulation in the skin. The skin is unique in that it can synthesize vitamin D from sunlight — but many people don’t get enough sun exposure, especially in northern latitudes or with indoor lifestyles. Deficiency has been associated with:

• Dry skin and impaired barrier function
• Worsening of inflammatory skin conditions (eczema, psoriasis)
• Impaired wound healing
• Increased skin infections

Vitamin D deficiency is extremely common, affecting an estimated 40-75% of adults in many populations. Given this high prevalence and vitamin D’s multiple effects on skin health, checking vitamin D status is worthwhile in anyone with persistent dry skin or inflammatory skin conditions.

Zinc:

Zinc is essential for skin health, playing roles in protein synthesis, cell division, wound healing, and immune function. It’s required for the proper function of hundreds of enzymes in the body. Deficiency causes distinctive skin changes:

• Dry, rough skin
• Acrodermatitis enteropathica pattern — dermatitis concentrated around body openings (mouth, eyes, nose, perineum) and on hands and feet
• Red, scaly, crusted patches
• Poor wound healing — wounds that don’t heal or heal very slowly
• Hair loss
• Brittle nails with white spots

Zinc deficiency can occur with malabsorption (celiac disease, inflammatory bowel disease), vegetarian/vegan diets (zinc from plant sources is less bioavailable), chronic diarrhea, certain medications (diuretics, proton pump inhibitors), chronic liver disease, or simply inadequate dietary intake. Older adults are at higher risk.

Iron:

Iron deficiency is the most common nutritional deficiency worldwide and affects skin in several ways:

• Dry, rough skin — often with fine, dry scaling
• Pale skin (from anemia — reduced hemoglobin gives skin less color)
• Itching (pruritus) — a common complaint with iron deficiency
• Brittle, spoon-shaped nails (koilonychia) — the nails become thin, soft, and concave
• Angular cheilitis — painful cracks at the corners of the mouth
• Glossitis — smooth, sore tongue
• Hair loss

B Vitamins:

Several B vitamins affect skin health through various mechanisms:

• Biotin (B7): Deficiency causes a characteristic scaly, red, seborrheic-like rash around the eyes, nose, and mouth, along with hair loss. Biotin deficiency is uncommon but can occur with certain medications, excessive raw egg white consumption (raw eggs contain a biotin-binding protein), or rare genetic conditions.
• Riboflavin (B2): Deficiency causes seborrheic dermatitis-like rash (oily, scaly patches), angular cheilitis (cracks at mouth corners), and glossitis (sore tongue).
• Niacin (B3): Severe deficiency causes pellagra — the “4 D’s”: dermatitis, diarrhea, dementia, and death (if untreated). The dermatitis is characteristic: symmetric, affecting sun-exposed areas with a clear demarcation at clothing lines. The affected skin is red, thickened, and scaly. Pellagra is rare in developed countries but can occur with alcoholism, severe malabsorption, or certain medications.
• B12: Deficiency more commonly causes neurological and blood abnormalities than skin changes, but can contribute to skin hyperpigmentation and hair changes.

What to test:

Vitamin D (25-hydroxyvitamin D) — given high prevalence of deficiency and its effects on skin, this should be checked broadly in anyone with skin concerns.

Ferritin and iron — for iron status. Ferritin reflects iron stores; low ferritin can indicate deficiency even before anemia develops.

Zinc — if risk factors present (vegetarian diet, malabsorption, chronic illness) or classic signs of zinc deficiency.

Vitamin A — if malabsorption suspected, very restrictive diet, or classic signs of deficiency (night blindness, follicular hyperkeratosis).

Vitamin B12 — though B12 deficiency more commonly causes neurological than skin symptoms, it’s worth checking if other deficiencies are present or if risk factors exist.

Complete blood count — can suggest nutritional deficiencies. Microcytic anemia suggests iron deficiency; macrocytic anemia suggests B12 or folate deficiency.

Hormonal Changes

Hormones have profound effects on skin — regulating oil production, skin thickness, moisture content, and cell turnover. When hormones change, whether due to natural life transitions, medical conditions, or treatments, skin often changes too. Dry skin is a particularly common result of several hormonal shifts.

Menopause and perimenopause:

Many women notice significant skin changes during the menopausal transition, with dry skin being one of the most common complaints. These changes often begin in perimenopause (the years leading up to menopause) and become more pronounced after menopause. Estrogen has substantial effects on skin:

• Sebum production: Estrogen stimulates sebaceous glands. As estrogen declines, sebum production decreases, reducing the natural oil that keeps skin supple and prevents water loss. Postmenopausal women may produce significantly less sebum than premenopausal women.
• Collagen production: Estrogen promotes collagen synthesis. Loss of estrogen leads to reduced collagen, making skin thinner and less resilient. Studies show women lose about 30% of skin collagen in the first 5 years after menopause.
• Skin hydration: Estrogen supports the production of hyaluronic acid and other substances that bind water in the skin. Declining estrogen reduces the skin’s water-holding capacity.
• Blood flow: Estrogen affects blood vessel function. Reduced estrogen can decrease blood flow to the skin.
• Skin microbiome: Hormonal changes affect the bacteria and other organisms living on the skin, which can influence skin health.

The result is that postmenopausal skin tends to be drier, thinner, less elastic, and more prone to irritation and wrinkling. While this is a normal hormonal effect, understanding the cause can guide management strategies.

Androgen changes:

Androgens (testosterone, DHEA, and related hormones) stimulate sebaceous glands — this is why teenage boys (with surging androgens) often have oily skin and acne. Changes in androgen levels affect skin oiliness:

• Low androgens (from aging, medical conditions, or medications like anti-androgens or GnRH agonists) can contribute to dry skin by reducing sebum production
• In women, the relative decline in androgens after menopause (androgens decline more slowly than estrogen but still decline) contributes to dry skin
• In men, declining testosterone with age (sometimes called “andropause”) may contribute to skin changes, though this is less dramatic than female menopause

What to test:

FSH (Follicle-Stimulating Hormone) and estradiol can confirm menopausal status if it’s unclear from symptoms. Elevated FSH with low estradiol indicates menopause.

Testosterone in men if low testosterone is suspected as a contributing factor, especially if accompanied by other symptoms (fatigue, low libido, decreased muscle mass).

DHEA-S — an adrenal androgen that affects sebum production. Very low levels may contribute to skin dryness.

Kidney Disease

Chronic kidney disease commonly causes dry, itchy skin — in fact, skin symptoms affect up to 80% of people with advanced kidney disease.

How kidney disease causes dry skin:

• Reduced sweat gland function: Uremic toxins affect sweat glands
• Impaired sebum production: Oil glands produce less sebum
• Dehydration: Fluid balance issues affect skin hydration
• Uremic pruritus: Intense itching related to kidney failure, leading to scratching and skin damage
• Metabolic changes: Calcium, phosphorus, and parathyroid hormone imbalances affect skin

Characteristics:

• Dry, rough, scaly skin
• Often accompanied by severe itching
• Scratch marks from itching
• May have yellowish or grayish tinge
• Often occurs in context of known kidney disease, but can be an early sign

What to test:

Creatinine and eGFR assess kidney function.

BUN provides additional information.

Liver Disease

The liver plays important roles in metabolism, including processing fats and vitamins essential for skin health. Liver disease can manifest with skin changes including dryness.

How liver disease affects skin:

• Impaired fat-soluble vitamin absorption and metabolism (A, D, E, K)
• Hormonal imbalances (liver metabolizes hormones)
• Bile salt accumulation causing itching
• Poor nutrition in advanced disease

Other skin signs of liver disease:

• Jaundice (yellow skin and eyes)
• Spider angiomas (small red spider-like blood vessels)
• Palmar erythema (red palms)
• Pruritus (itching, especially with cholestatic liver disease)

What to test:

ALT and AST — liver enzymes indicating liver cell damage.

Albumin and bilirubin — markers of liver synthetic function.

GGT and ALP — elevated in cholestatic (bile flow obstruction) liver disease.

Dehydration

While drinking more water won’t cure dry skin caused by thyroid disease or diabetes, actual dehydration does affect skin hydration. Chronic mild dehydration is common and can contribute to dry skin.

Signs of dehydration affecting skin:

• Decreased skin turgor — skin tents when pinched
• Dry mucous membranes (dry mouth, cracked lips)
• Dark urine
• Thirst
• Fatigue

Blood tests aren’t typically needed to diagnose dehydration from inadequate fluid intake, but can identify causes of excessive fluid loss (diabetes, kidney disease).

Skin Conditions That Cause Dryness

Some primary skin conditions cause dryness that blood tests won’t identify but are important to consider.

Eczema (atopic dermatitis):

An inflammatory skin condition with genetic and immune components. Characterized by:

• Dry, itchy patches
• Typically affects specific areas (elbow creases, behind knees, face in children)
• Often starts in childhood
• Associated with asthma, hay fever, food allergies
• Flares and remissions

Psoriasis:

An autoimmune condition causing rapid skin cell turnover:

• Thick, silvery, scaly plaques
• Typically affects elbows, knees, scalp, lower back
• Distinct from simple dry skin but includes dryness component

Ichthyosis:

A group of genetic conditions causing severe scaling and dryness:

• Often present from birth or early childhood
• Fish-scale appearance
• Varying severity

These conditions are diagnosed clinically rather than with blood tests, though blood tests may rule out contributing systemic conditions.

Medications That Cause Dry Skin

Many medications can cause or worsen dry skin:

• Retinoids (isotretinoin, tretinoin) — commonly cause significant dryness
• Diuretics — cause fluid loss affecting skin hydration
• Statins — can affect skin barrier
• Antihistamines — dry skin as side effect of anticholinergic action
• Acne medications — benzoyl peroxide, salicylic acid are drying
• Chemotherapy — many agents affect rapidly dividing skin cells
• Certain blood pressure medications

If dry skin started after beginning a new medication, review this possibility with your healthcare provider.

The Testing Strategy for Dry Skin

When dry skin persists despite good skincare, is accompanied by other symptoms, or represents a change from baseline, blood testing can identify internal causes.

Core tests for unexplained dry skin:

Thyroid panel (essential):

• TSH
• Free T4
• TPO antibodies

Blood sugar:

• Fasting glucose
• HbA1c

Kidney function:

• Creatinine
• eGFR

Nutritional status:

• Vitamin D
• Ferritin
• CBC

Liver function:

• ALT
• AST

Additional tests based on symptoms:

• If menopausal symptoms: FSH, estradiol
• If malabsorption suspected: vitamin A, zinc, additional nutritional markers
• If severe or refractory: comprehensive metabolic panel, additional workup

What to Do With the Results

If hypothyroidism is found:

Treatment with thyroid hormone replacement typically improves skin over weeks to months. As thyroid levels normalize, sebum production increases, skin cell turnover normalizes, and the skin becomes softer and more supple. Many people notice skin improvement as one of the first signs that their thyroid treatment is working.

If diabetes or prediabetes is found:

Improving blood sugar control through diet, exercise, and possibly medication helps skin health. Better glucose control reduces dehydration, improves circulation, and supports skin barrier function. Meticulous foot care becomes especially important.

If nutritional deficiencies are found:

Supplementation to correct deficiencies typically improves skin over time. Vitamin D repletion, iron correction, and other nutritional optimization support skin health from the inside.

If kidney disease is found:

Managing kidney disease and working with a nephrologist is essential. Skin care becomes part of the overall management plan.

When Tests Are Normal

Normal blood tests mean the internal conditions tested for aren’t present. Consider:

• Environmental factors: Low humidity, cold weather, hot showers, harsh soaps, over-washing — these remain the most common causes of dry skin
• Aging: Skin naturally becomes drier with age as sebum production decreases and skin thins
• Genetic predisposition: Some people simply have drier skin than others
• Primary skin conditions: Eczema, psoriasis, and ichthyosis are diagnosed clinically
• Occupational exposure: Frequent handwashing, chemical exposure, etc.
• Medication effects: Review all medications
• Subclinical changes: Values in the “normal” range but not optimal for you

Skincare Strategies

While addressing internal causes is crucial for lasting improvement, proper skincare helps manage dry skin and supports skin barrier repair. These strategies work alongside — not instead of — treating underlying conditions.

Bathing and cleansing:

• Moisturize immediately after bathing — within 3 minutes, while skin is still slightly damp. This locks in moisture before it evaporates. This timing is one of the most important factors in effective moisturizing.
• Use lukewarm, not hot water — hot water strips oils from the skin. Shorter, cooler showers are gentler on the skin barrier.
• Limit bathing time — long soaks actually dehydrate skin by stripping natural oils. Aim for 5-10 minutes.
• Use gentle, fragrance-free cleansers — avoid harsh soaps, antibacterial soaps, and anything that makes your skin feel “squeaky clean” (that feeling means natural oils have been stripped). Look for cleansers labeled “for sensitive skin” or “soap-free.”
• Pat dry, don’t rub — aggressive toweling damages the skin barrier.

Moisturizing:

• Choose appropriate moisturizer strength — for very dry skin, thicker is better. From lightest to heaviest: lotions < creams < ointments. Ointments (like petroleum jelly) are most effective but feel greasy. Creams are a good middle ground.
• Look for key ingredients:
  • Occlusives (petroleum, mineral oil, lanolin) — form a barrier to prevent water loss
  • Humectants (glycerin, hyaluronic acid, urea) — draw water into the skin
  • Emollients (ceramides, fatty acids, cholesterol) — fill in gaps between skin cells and repair the barrier
• Moisturize multiple times daily — not just after bathing. Hands may need moisturizing after every wash.
• Apply to damp skin — moisturizers work best when there’s water to trap.

Environmental modifications:

• Use a humidifier — especially in winter when indoor heating dries the air. Aim for 40-60% humidity.
• Avoid extreme temperatures — both hot and cold dry the skin.
• Protect skin from wind and cold — cover exposed skin with gloves, scarves, and appropriate clothing.
• Use sunscreen year-round — sun damage impairs skin barrier function.

Lifestyle factors:

• Stay hydrated — adequate fluid intake supports overall health including skin. While drinking extra water won’t cure dry skin from internal causes, dehydration definitely makes skin worse.
• Avoid irritants — certain fabrics (wool, synthetic materials), chemicals, fragrances, and detergents can irritate dry skin. Use fragrance-free laundry detergent and avoid fabric softeners if skin is sensitive.
• Wear soft, breathable fabrics — cotton is generally well-tolerated.
• Don’t scratch — scratching damages the skin barrier and can lead to infection. Keep nails short, and try cold compresses or anti-itch treatments if itching is problematic.

When to see a dermatologist:

• Dry skin that’s severe, cracking, or bleeding
• Signs of infection (redness, warmth, pus, fever)
• Dry skin that doesn’t improve with good skincare and normal blood tests
• Concern for a primary skin condition (eczema, psoriasis)
• Rashes or skin changes beyond simple dryness

The Bottom Line

Dry skin is extremely common, and most cases are caused by environmental factors and skincare habits — cold weather, low humidity, hot showers, harsh soaps, aging, and inadequate moisturizing. These external causes respond to external solutions: better moisturizers, humidifiers, gentler cleansers, and cooler showers.

But when dry skin persists despite your best topical efforts, doesn’t respond to typical remedies, or is accompanied by other symptoms, an internal cause may be at play. Your skin is a window into your internal health, and persistent dry skin can be one of the first visible signs that something inside needs attention.

Hypothyroidism is the classic systemic cause of dry skin — and it’s common enough (affecting about 5% of adults) that thyroid testing should be considered in anyone with unexplained, persistent dry skin, especially if fatigue, cold intolerance, or weight changes are also present. The dry, rough, pale skin of hypothyroidism is characteristic enough that experienced clinicians can often suspect the diagnosis just by looking — but blood tests confirm it.

Diabetes, nutritional deficiencies, kidney disease, liver disease, and hormonal changes (especially menopause) are other internal factors that commonly manifest as dry skin. Each has its own pattern and associated symptoms that provide diagnostic clues.

Blood testing can identify these treatable conditions:

• A simple thyroid panel (TSH, Free T4, TPO antibodies) can diagnose hypothyroidism
• Blood sugar tests (fasting glucose, HbA1c) can identify diabetes or prediabetes
• Kidney function tests (creatinine, eGFR) can detect kidney disease
• Nutritional markers (vitamin D, ferritin) can identify deficiencies

Finding and addressing the underlying cause — rather than just applying more moisturizer — can transform skin health from the inside out. When your thyroid is treated, when your blood sugar is controlled, when your nutritional deficiencies are corrected, your skin often improves in ways that no topical product alone could achieve.

You don’t have to accept chronically dry, uncomfortable skin as inevitable. If moisturizer isn’t enough, it’s worth finding out why — and treating the real cause.

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Key Takeaways

• Persistent dry skin that doesn’t respond to moisturizer may have an internal cause
• Hypothyroidism is the classic systemic cause of dry skin — reduced thyroid function decreases sebum production and slows skin cell turnover
• Diabetes affects skin through dehydration, poor circulation, and nerve damage — dry skin may be an early sign
• Nutritional deficiencies affect skin health — vitamin D, iron, zinc, and essential fatty acids are particularly important
• Hormonal changes, especially menopause, commonly cause dry skin — declining estrogen reduces sebum production
• Kidney and liver disease can manifest with skin symptoms
• Key tests include thyroid panel, blood sugar, kidney function, and vitamin D
• Treating the underlying condition often improves skin — thyroid treatment, diabetes control, and nutritional repletion all help
• Good skincare remains important even while addressing internal causes
• If tests are normal, environmental factors and primary skin conditions are more likely