Two skin stories. Both instructive.
My girlfriend's acne appeared in her early twenties. Jawline, chin, and neck. Persistent, painful, cyclical. She tried topical treatments, prescription retinoids, antibiotics, and a rotating cast of cleansers and serums. Some helped temporarily. None resolved it. It wasn't until her PCOS diagnosis that anyone connected the acne to her hormonal profile. Elevated testosterone, low SHBG, insulin resistance driving the whole picture. The acne wasn't a skin problem. It was an androgen problem expressing itself through her skin.
The second story is someone I work with. Early twenties, cystic acne across her cheeks and back since her teens. She'd spent thousands on skincare products and clinic treatments. When she finally got blood work done, her DHEAS (an adrenal androgen) was elevated and her zinc was low. Not dramatically. Moderately. Enough that her GP adjusted the approach from purely topical to include hormonal management and zinc supplementation. Within three months, her skin had improved more than it had in years of topical-only treatment.
I'm writing this article because the skincare industry in Australia is worth billions. The shelves are full of products promising clear skin through cleansers, serums, acids, and masks. And for many people (those with contact dermatitis, rosacea, or environmentally triggered skin issues) topical treatment is exactly right.
But for a significant proportion of people with persistent, treatment-resistant skin problems, the cause is internal. Hormonal. Metabolic. Nutritional. And no amount of topical product will address a cause that's circulating in the bloodstream.
A note before we get into it
General information only. I'm not a dermatologist. Skin conditions have many causes, and blood tests can help identify some of them, not all. If you have severe, widespread, or rapidly changing skin conditions, see a dermatologist.
This article focuses on the blood markers most commonly linked to skin problems, particularly hormonal acne. It doesn't cover skin cancer screening, allergic skin conditions, or autoimmune skin diseases in detail.
Your skin as a signal, not just a surface
Your skin is the largest organ in your body, and it reflects what's happening inside. Often more honestly than any other system. Hormonal shifts can show up as acne. Iron deficiency can show up as pallor and dark circles. Thyroid dysfunction can show up as dry, coarse, or thinning skin. Blood sugar problems can show up as skin tags and darkened skin folds. Liver dysfunction can show up as jaundice, spider naevi, or itching.
Dermatologists have known this for decades. Internal medicine and dermatology overlap far more than most people realise. A good dermatologist doesn't just look at the skin. They consider what the skin reveals about the body beneath.
Blood tests are one way to listen to that signal.
Hormonal acne: the blood test case
Hormonal acne is the single strongest case for blood testing in dermatology. Here's why.
The pattern: Acne concentrated on the lower face (jawline, chin, neck), often cyclical (worsening before menstruation), frequently cystic or nodular (deep, painful lesions rather than superficial blackheads or whiteheads), and resistant to standard topical treatments.
The mechanism: Androgens (testosterone, DHT, DHEAS) stimulate sebaceous glands, increasing oil production and promoting the follicular plugging that leads to acne. When androgens are elevated, whether from PCOS, adrenal androgen excess, or idiopathic hyperandrogenism, the skin becomes an output for the hormonal imbalance.
Why topical treatment alone often fails: If the driver is circulating hormones, treating the skin surface is treating the symptom, not the cause. It's like mopping a floor while the tap is still running. Topical treatments can reduce the expression, but the hormonal driver keeps pushing oil production and inflammation.
Who's affected: Women with PCOS (the most common cause of hormonal acne in women), women with adrenal androgen excess, women in perimenopause (hormonal shifts can trigger adult-onset acne), and some men with androgen-related skin issues.
The full skin-relevant blood panel
Testosterone, SHBG, and DHEAS
The core hormonal markers
These are the primary hormonal markers for acne investigation in women.
Total testosterone may be elevated in PCOS or androgen excess disorders.
Free testosterone and SHBG: SHBG (sex hormone binding globulin) binds testosterone and reduces its biological activity. When SHBG is low (often driven by insulin resistance), more free testosterone is available to act on sebaceous glands, even if total testosterone looks borderline. Low SHBG is often the smoking gun in hormonal acne.
DHEAS is an adrenal androgen. Elevated DHEAS suggests the adrenal glands are contributing to the androgen picture. This is relevant in younger women and those without classic PCOS features.
Test it with Bloody Good:
Product: Free Testosterone + SHBG Blood Test
Product: DHEAS Blood Test
Related reading: PCOS Blood Tests · Testosterone Testing
Thyroid Function
How it affects your skin
Hypothyroidism can cause dry, coarse, thickened skin, brittle nails, thinning hair, and a yellowish complexion. Hyperthyroidism can cause warm, moist, flushed skin and pretibial myxoedema. Both conditions can affect skin texture and appearance, often attributed to ageing or environmental factors.
Test it with Bloody Good:
Product: Thyroid Function Test (TFT)
Related reading: Thyroid Function Tests
Iron and Ferritin
The skin signs of low iron
Iron deficiency can produce pallor (noticeable in the face and nail beds), dark under-eye circles, and brittle nails. Severe deficiency can cause koilonychia (spoon-shaped nails). Adequate iron is also involved in wound healing and skin repair.
Test it with Bloody Good:
Product: Iron Studies (Including Ferritin)
Related reading: Iron and Ferritin Blood Tests
Zinc
Skin cell turnover and repair
Zinc is involved in skin cell turnover, wound healing, immune function at the skin level, and sebaceous gland regulation. Low zinc has been associated with acne, slow wound healing, dermatitis, and increased susceptibility to skin infections.
Zinc supplementation has been studied as an acne treatment and shows moderate benefit, particularly in people who are actually deficient. Testing confirms whether supplementation is warranted rather than supplementing blindly.
Test it with Bloody Good:
Product: Zinc Blood Test
Vitamin D
Immune modulation and skin health
Vitamin D receptors are present throughout the skin, and vitamin D has roles in skin cell growth, repair, and immune modulation. Low vitamin D has been associated with psoriasis severity, eczema flares, and impaired wound healing. Some studies have found lower vitamin D levels in acne patients compared to controls, though the relationship is less well-established than for hormones.
Blood Sugar and Insulin
The metabolic connection to skin
Insulin resistance drives several skin manifestations. Acanthosis nigricans (darkened, velvety patches of skin, typically in the neck folds, armpits, or groin) is a clinical sign of insulin resistance. Skin tags in these areas are another associated finding.
Insulin resistance also exacerbates acne by suppressing SHBG (freeing more testosterone to act on skin) and by promoting inflammation. Addressing insulin resistance through diet, exercise, and sometimes metformin can improve both the metabolic picture and the skin.
Test it with Bloody Good:
Product: Fasting Insulin Blood Test
Product: HbA1c Blood Test
Related reading: HbA1c Explained · Weight Gain Blood Tests
Liver Function
Hormone metabolism and medication monitoring
The liver metabolises hormones, including androgens. Impaired liver function can alter hormone clearance and contribute to androgenic skin symptoms. Elevated liver enzymes can also produce skin manifestations like jaundice, spider angiomas, and palmar erythema.
If you're on oral acne medications (particularly isotretinoin), liver function monitoring is standard because these medications can stress the liver.
CRP (Inflammation)
Systemic inflammation and skin
Inflammatory skin conditions (severe acne, eczema flares, psoriasis) exist within a systemic inflammatory context. Elevated hs-CRP alongside skin problems suggests the inflammation isn't purely local. There may be a systemic component that could respond to anti-inflammatory strategies beyond topical treatment.
Test it with Bloody Good:
When skin problems are NOT a blood test issue
Contact dermatitis. Triggered by external allergens or irritants (cosmetics, fragrances, nickel, latex). This is a patch testing issue, not a blood test issue.
Rosacea. A chronic inflammatory skin condition affecting the face. It has a distinct pathology and is primarily diagnosed clinically. Blood tests don't diagnose it.
Fungal skin infections. Ringworm, tinea, candida. Diagnosed by skin scraping or culture, not blood test.
Allergic eczema (atopic dermatitis). While blood markers can show elevated IgE and eosinophils in atopic individuals, management is primarily clinical and topical.
Genetic skin conditions. Psoriasis has a genetic and autoimmune component. Blood tests (CRP, liver function for methotrexate monitoring) play a supporting role, but the diagnosis is clinical.
Sunburn, heat rash, and environmental skin reactions. These are external, not internal.
Who should be testing
Women with persistent acne concentrated on the lower face, jawline, and chin, particularly if it's cyclical, cystic, or treatment-resistant. Hormonal investigation is strongly indicated.
Women with acne alongside other androgenic symptoms like irregular periods, hirsutism (excess facial or body hair), or hair thinning on the scalp. PCOS screening is worth discussing with your GP.
Anyone with skin changes alongside metabolic symptoms such as weight gain, fatigue, temperature sensitivity (thyroid), or darkened skin folds (insulin resistance).
Anyone with persistent skin problems and multiple nutritional gaps like iron, zinc, or vitamin D depletion alongside skin issues. This suggests a systemic cause worth investigating.
Anyone on isotretinoin or considering it. Liver function and lipid monitoring are standard before and during treatment.
How to prepare
Fast for 8 to 12 hours if including blood sugar and insulin markers.
Test in the morning. Testosterone and SHBG are most consistent from a morning draw.
Women: test on day 2 to 5 of your cycle if investigating hormonal acne. This is the early follicular phase when baseline hormone levels are most interpretable. If your periods are irregular, test any time and note the date.
Stop biotin supplements 48 to 72 hours before. Biotin is found in many skin, hair, and nail supplements and can interfere with hormone assays.
Tests to consider through Bloody Good
Hormonal acne panel (women)
Testosterone Free/Total + SHBG for the androgen picture.
DHEAS Blood Test for adrenal androgen contribution.
Fasting Insulin to check whether insulin resistance is driving SHBG down.
HbA1c for metabolic context.
Nutritional skin markers
Iron Studies (Including Ferritin) for pallor, dark circles, wound healing.
Zinc Blood Test for skin cell turnover and sebaceous regulation.
Vitamin D (25-OH) for skin immune modulation.
Broader context
Thyroid Function Test (TFT) for skin texture and dryness.
Liver Function Test (LFT) for hormone metabolism and isotretinoin monitoring.
High-Sensitivity CRP for systemic inflammation.
Full Blood Count (FBC) as a baseline.
Full coverage
The Bloody Good Test covers 100 biomarkers including hormones, iron, thyroid, liver, inflammation, and metabolic markers. Pair with standalone DHEAS and zinc tests for the most thorough skin-focused investigation available.
What to do after testing
If androgens are elevated (testosterone, DHEAS, low SHBG): Discuss hormonal management with your GP. Options may include combined oral contraceptive pill (anti-androgenic types), spironolactone (an androgen receptor blocker used off-label for acne), or metformin if insulin resistance is driving the picture. Topical treatments alongside hormonal management typically produce the best outcomes.
If insulin resistance is present: Address it metabolically. Diet, exercise, sleep, stress management. Improving insulin sensitivity can raise SHBG, reduce free testosterone, and often improve skin as a downstream effect.
If zinc is low: Supplement under guidance. Zinc glycinate or picolinate at moderate doses (15 to 30 mg daily). Improvements in skin are gradual. Expect two to three months.
If thyroid is abnormal: Treatment addresses the skin changes alongside all other thyroid symptoms. Dry, coarse skin from hypothyroidism typically improves within months of achieving thyroid balance.
If iron is low: Supplement. Pallor and dark circles may improve as ferritin rises, though this takes weeks to months.
If everything's normal: The cause is likely external (contact, environmental), structural (rosacea, genetic), or stress-related. A dermatologist can provide clinical assessment and targeted treatment.
Explore more biomarkers
Browse the Bloody Good Biomarker Directory
General information only. This article is not medical advice and is not a substitute for care from a qualified health professional. If you have concerning symptoms or urgent health issues, seek medical attention promptly.