Blood Tests for Skin Problems
Acne, eczema, rashes, and slow healing often have internal causes that a blood test can reveal. Stop treating symptoms and find the root cause.
Your Skin Is a Window Into Your Health
Dermatologists have long known that the skin reflects internal health. Persistent acne in your 30s, eczema that will not clear, unexplained rashes, and slow wound healing are often signs that something is off inside \u2014 not just on the surface. Yet most people are treated with topical creams and antibiotics without ever getting a blood test.
Research shows that up to 50% of adult acne patients have an identifiable hormonal or metabolic abnormality on blood testing, and over 30% of eczema patients have nutritional deficiencies that worsen their condition. The right blood tests can transform your skin treatment from guesswork to precision.
The 8 Blood Tests for Better Skin
1. Hormones (Testosterone, DHEA-S, SHBG)
Why this matters: Hormonal acne is the number one reason adults develop persistent breakouts. Androgens (male hormones present in both sexes) stimulate sebaceous glands to produce excess oil, which clogs pores and feeds acne-causing bacteria. Even mildly elevated testosterone or DHEA-S can trigger severe cystic acne along the jawline, chin, and neck. Low SHBG (sex hormone-binding globulin) means more free testosterone is available to wreak havoc on your skin.
Optimal levels: Women: Free testosterone below 2.5 nmol/L, DHEA-S below 10 µmol/L, SHBG above 40 nmol/L. Men: Total testosterone within range but look at free testosterone if acne is persistent. DHEA-S peaks in your 20s and declines — elevated DHEA-S at any age suggests adrenal overactivity.
Watch out: In women, hormonal acne plus irregular periods plus weight gain is the classic triad of PCOS (polycystic ovary syndrome). PCOS affects up to 13% of women and is one of the most treatable causes of adult acne. Ask for insulin and LH/FSH if PCOS is suspected.
2. Zinc
Why this matters: Zinc is critical for skin repair, immune function, and inflammation control. It reduces the activity of 5-alpha reductase (the enzyme that converts testosterone to the more potent DHT) and inhibits the inflammatory response to acne bacteria. Multiple studies have shown that acne patients have significantly lower zinc levels than age-matched controls. Zinc also plays a role in eczema — deficiency impairs the skin barrier, allowing allergens and irritants to penetrate more easily.
Optimal levels: Serum zinc should be above 12 µmol/L, ideally above 15 µmol/L for skin health. Note that zinc levels naturally drop during infection and inflammation, so a single low result should be confirmed with a repeat test. Zinc is best tested fasting in the morning.
Watch out: Zinc competes with copper for absorption. Long-term high-dose zinc supplementation (>40mg/day) can cause copper deficiency. If supplementing zinc, consider a zinc/copper ratio of 15:1. Also, zinc supplements should be taken with food to avoid nausea.
3. Vitamin D (25-OH)
Why this matters: Vitamin D is a potent immune modulator that regulates the skin’s innate defence system. It controls the production of antimicrobial peptides (cathelicidin and defensins) that kill acne-causing bacteria. Low vitamin D is also strongly associated with eczema severity — a 2019 meta-analysis showed that vitamin D supplementation significantly reduced eczema flares. Psoriasis patients consistently have lower vitamin D levels, and topical vitamin D analogues are a first-line psoriasis treatment.
Optimal levels: Aim for 75–150 nmol/L (30–60 ng/mL). Below 50 nmol/L is deficient and associated with worse skin outcomes. In Australia, vitamin D testing is bulk-billed when there is a clinical indication such as skin disease or limited sun exposure.
Watch out: Paradoxically, many people with skin problems avoid the sun (because of photosensitivity or cosmetic concern), which worsens their vitamin D status. Moderate, regular sun exposure (10–15 minutes on arms before 10am or after 3pm) plus supplementation if deficient is the recommended approach.
4. Liver Function Tests (LFTs)
Why this matters: The liver is the body’s primary detoxification organ, processing hormones, toxins, and waste products. When liver function is compromised, these substances accumulate and are shunted to the skin for elimination — resulting in acne, itching, yellowing, spider naevi, and dull complexion. Elevated GGT is particularly associated with oxidative stress that damages skin cells. Alcoholic liver disease, fatty liver, and medication side effects (isotretinoin, antibiotics) all affect the skin via liver pathways.
Optimal levels: ALT: below 35 U/L (men) and below 25 U/L (women). GGT: below 40 U/L. Bilirubin: 3–20 µmol/L. Albumin: 35–50 g/L (low albumin suggests poor nutrition or chronic disease, both of which worsen skin health).
Watch out: If you are taking isotretinoin (Roaccutane) for acne, your doctor should already be monitoring LFTs monthly. Elevated ALT during isotretinoin use is common and usually reversible, but levels above 3x the upper limit require stopping the medication.
5. Thyroid Panel (TSH, FT4)
Why this matters: The thyroid controls your skin’s metabolism, moisture retention, and turnover rate. Hypothyroidism causes dry, flaky, pale skin that bruises easily and heals slowly. The skin may appear puffy, particularly around the eyes. Hyperthyroidism causes warm, moist, thin skin with excessive sweating. Autoimmune thyroiditis (Hashimoto’s) is associated with chronic urticaria (hives) in up to 30% of cases — treating the thyroid often resolves the hives.
Optimal levels: TSH 1.0–2.5 mIU/L for optimal skin health. Free T4 in the upper half of reference range. If you have hives or unexplained itching, request thyroid antibodies (TPO, TG) even if TSH is normal.
Watch out: Dry skin is so common in hypothyroidism that dermatologists consider it a clinical sign. If you have dry, thickened skin that does not respond to moisturisers, plus fatigue and cold intolerance, thyroid testing should be your first step.
6. Iron Studies & Ferritin
Why this matters: Iron is essential for oxygen delivery to skin cells and for the enzymes that produce collagen. Iron deficiency causes pale skin, dark under-eye circles, brittle nails, and slow wound healing. It also worsens hair loss, which often accompanies skin problems. Interestingly, iron overload (haemochromatosis) also causes skin problems — a bronze or grey skin discolouration that is a classic clinical sign.
Optimal levels: Ferritin above 50 µg/L for skin health. Below 30 µg/L, skin healing is impaired and dark circles worsen. Above 300 µg/L in men or 200 µg/L in women, consider testing for haemochromatosis (transferrin saturation and HFE gene).
Watch out: Dark under-eye circles are often blamed on lack of sleep, but iron deficiency is one of the most common and treatable causes. If concealer is not helping, check your ferritin.
7. Blood Glucose & HbA1c
Why this matters: Insulin resistance is a powerful driver of acne, skin tags, and acanthosis nigricans (dark, velvety patches on the neck and armpits). High insulin levels stimulate androgen production and increase sebum output. The high-glycaemic Western diet spikes insulin repeatedly, and studies show that low-GI diets significantly reduce acne severity. Pre-diabetes and type 2 diabetes also impair wound healing and increase skin infection risk.
Optimal levels: Fasting glucose 4.0–5.4 mmol/L. HbA1c below 5.7% (39 mmol/mol). Fasting insulin below 10 mIU/L. Elevated fasting insulin with normal glucose is early insulin resistance — a treatable cause of acne that most GPs do not test for.
Watch out: Skin tags and acanthosis nigricans are visual markers of insulin resistance. If you have either of these, request fasting insulin even if your glucose is normal. Dietary changes (reducing sugar and refined carbohydrates) often improve both skin and metabolic markers within 8–12 weeks.
8. CRP & Inflammatory Markers
Why this matters: Chronic low-grade inflammation drives most inflammatory skin conditions: acne, eczema, psoriasis, rosacea, and urticaria. Elevated CRP indicates that your immune system is in overdrive, which manifests as red, inflamed, painful skin. Identifying the source of inflammation (gut dysbiosis, food sensitivities, autoimmune conditions) is the key to long-term skin improvement rather than just suppressing symptoms with topical steroids.
Optimal levels: CRP below 3 mg/L. High-sensitivity CRP below 1.0 mg/L. ESR within age-appropriate range. Persistently elevated CRP with skin disease should prompt investigation of underlying autoimmune conditions (ANA, anti-dsDNA if lupus is suspected).
Watch out: Many skin conditions (psoriasis, severe acne, eczema) themselves elevate CRP. This does not mean the CRP is irrelevant — it confirms systemic inflammation and can be used to track treatment response. A falling CRP indicates your treatment is working at a systemic level.
Which Tests for Which Skin Condition?
| Skin Condition | Top Blood Tests | Mechanism |
|---|---|---|
| Cystic Acne (jawline) | Testosterone, DHEA-S, SHBG, Insulin | Androgen excess → sebum overproduction |
| Eczema / Atopic Dermatitis | Vitamin D, Zinc, IgE, Thyroid | Immune dysregulation + barrier defect |
| Psoriasis | CRP, ESR, Vitamin D, Liver function | Autoimmune + systemic inflammation |
| Chronic Hives (Urticaria) | Thyroid antibodies, CRP, FBC, IgE | Autoimmune thyroiditis or mast cell activation |
| Rosacea | H. pylori, CRP, Vitamin D, Liver | Gut-skin axis + vascular inflammation |
| Dark Under-Eye Circles | Ferritin, Iron, FBC, Thyroid | Iron deficiency + poor oxygenation |
| Slow Wound Healing | HbA1c, Zinc, Vitamin C, Albumin | Metabolic + nutritional deficiency |
When Skin Changes Need Urgent Attention
New moles that are asymmetric, have irregular borders, multiple colours, or are larger than 6mm
Skin rash with fever, joint pain, or feeling generally unwell — possible autoimmune or infection
Rapidly spreading redness with warmth and pain — possible cellulitis (needs antibiotics urgently)
Yellowing of skin and eyes (jaundice) — needs immediate liver function testing
Purpuric rash (dark purple spots that do not blanch when pressed) — possible vasculitis or blood disorder
Blistering skin without trauma — possible autoimmune blistering disease
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SmarterBlood provides educational health information. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your doctor or dermatologist with questions about skin conditions.