What can a blood test tell you about your skin?

We spend a fortune on skincare (cleansers, creams, serums, supplements) all in the hope of improving our skin’s texture, tone, and glow. But, what if some of the answers to your skin concerns weren’t in a bottle, but in your blood?

That’s because your skin doesn’t just reflect what’s happening on the surface. It tells the story of what’s going on inside.

Your skin barrier is your body’s first line of defence — locking in moisture and keeping irritants, allergens, and pathogens out. When it’s strong, skin feels smooth and supple. When it’s compromised, you might experience dryness, redness, flakiness, or breakouts.

A healthy skin barrier relies on a finely tuned balance of nutrients, hormones, and internal systems. 

Here are nine areas that you can test to help unlock the secrets behind your skin health: 

1. Stress and cortisol
2. Blood sugar and skin ageing
3. Hormones and skin vitality
4. Inflammation and skin conditions
5. Nutrients that support the skin barrier
6. Essential fatty acids and skin hydration
7. Thyroid health and skin texture
8. Liver and kidney function
9. Immune function and allergies

 

Nine insights your blood can reveal about your skin

 

1. Stress and cortisol

Chronic stress doesn’t just mess with your head, it messes with your skin. Too much cortisol over long periods is linked to reduced collagen production, leading to thinner skin and more fine lines. It may also increase oil production and inflammation, triggering breakouts or flare-ups.

If you’re noticing changes in your skin alongside mood swings, poor sleep, or fatigue, your stress response could be the link.

Biomarker to check: cortisol

2. Blood sugar and skin ageing

Consistently high blood sugar (as well as oxidative stress and UV exposure) can contribute to a process called glycation, where sugar molecules stick to proteins like collagen and elastin, making them stiff and less springy. Over time, this can lead to more wrinkles, less firmness, and slower healing.

Poor blood sugar control can also increase your risk of skin infections and impair your skin’s ability to repair itself, as seen in diabetes. The biomarker HbA1c helps measure your blood sugar control. While it can't measure the degree of glycation, it can help rule out diabetes and whether you might be consuming too much sugar. 

Biomarker to check: HbA1c

3. Hormones and skin vitality

Your hormones are behind the scenes, directing how much oil your skin produces, its thickness/firmness, and how vibrant it looks.

Here are some of the most common hormonal imbalances that affect the skin:

• Low oestradiol in women (common post-menopause) can make skin drier, thinner, and less elastic
• High testosterone (common in PCOS) may cause acne and unwanted hair growth
• Fluctuating hormone levels can increase inflammation, throw off sebum production, and affect overall texture

If your skin concerns shift with your cycle, pregnancy, menopause, or androgens — hormones could be the missing piece.

Biomarkers to check: FSH, LH, oestradiol, testosterone, free testosterone, free androgen index, SHBG

4. Inflammation and skin conditions

Low-level, chronic inflammation can silently sabotage your skin. While a little inflammation is essential for healing, too much might be due to factors like poor sleep, stress, a lack of exercise, which could have implications for conditions like eczema, rosacea, and psoriasis, or make your skin appear to age faster.

CRP (C-reactive protein) is a general marker of inflammation in the body. If it’s elevated, your skin might be caught in the crossfire.

Biomarker to check: hs-CRP

5. Nutrients that support the skin barrier

Your skin barrier needs the right building blocks to function, and many of those come from your diet. Key nutrients help you make collagen, maintain hydration, support repair, and fight off damage from the environment.

Low levels of certain vitamins and minerals can leave your skin looking dull, dry, or uneven.

Nutrient highlights:

• Zinc is essential for wound healing, reducing inflammation, protecting against free radical damage, and maintaining the skin’s barrier function
• Vitamin D supports immune defence and skin cell turnover — low levels are linked to acne and psoriasis
• Iron, folate, and B12 support oxygen delivery to the skin, which helps prevent dullness, pallor, and pigmentation issues

Biomarkers to check: zinc, folate, vitamin B12, vitamin D, and iron studies

6. Essential fatty acids and skin hydration

Your skin’s hydration and suppleness depend heavily on your fatty acid profile, especially the balance between omega-3 and omega-6 fatty acids. These healthy fats help maintain the skin barrier, lock in moisture, and calm inflammation.

When the balance is off, you might notice more dryness, irritation, or flare-ups like acne and eczema.

Omega-3 benefits for your skin:

• A higher omega-3 index and lower ARA: EPA ratio may reduce dryness and support conditions like eczema and acne
• Omega-3s help strengthen the skin barrier, locking in moisture and calming irritation

Biomarkers to check: omega-3 index, ARA :EPA ratio

7. Thyroid health and skin texture

Your thyroid doesn’t just influence your metabolism and energy levels – it also plays a key role in how your skin looks and feels. That’s because thyroid hormones help regulate skin cell turnover, moisture levels, and the structure of hair and nails. 

When your thyroid isn’t working as it should, it can show up on the outside long before you feel any other symptoms.

• An underactive thyroid (hypothyroidism) can slow down skin renewal, leading to pale, dry, or scaly skin that may feel rough to the touch. You might also notice brittle nails, coarse hair, and slower wound healing. Some people become more prone to skin conditions like eczema or dermatitis.
• An overactive thyroid (hyperthyroidism) can have the opposite effect, speeding things up. This might cause your skin to feel unusually warm and sweaty (a condition called hyperhidrosis), and your hair and nails may become thin, soft, and more fragile.

Biomarkers to check: TSH, FT3, FT4

8. Liver and kidney function

Your liver and kidneys help clear waste and toxins from your body, and if they’re not working optimally, your skin can pay the price, leading to skin discolouration, rashes, or sallow skin.

Common signs of dysfunction include:

• Liver issues: itchy skin, rashes, or yellowing (jaundice)
• Kidney issues: dry, dull, or sallow skin

Biomarkers to check: ALT, GGT, bilirubin, urea, creatinine, eGFR

9. Immune function and allergies

Your immune system plays a critical role in how your skin responds to the world around you. Allergies, sensitivities, and autoimmune conditions can all leave their mark, whether through rashes, hives, or chronic inflammation.

A full blood count can help you understand how your immune system is performing.

Biomarkers to check: White blood cell count and subtypes

 

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References: 

1. Qure Skincare, 2023. How cortisol affects the skin: The stress-skin connection and what you can do. [online] Qure Skincare. [Accessed 19 May 2025].
2. Chiarelli, F., Santilli, F. and Mohn, A., 2009. Role of growth factors in diabetic microangiopathy. Acta Diabetologica, 46(4), pp.217–226.
3. Rzepecki, A.K., Mu, E.W., Chen, T. and Meehan, S.A., 2019. A review of hormonal influences on acne. Dermato-Endocrinology, 11(1), p.e1621812.
4. Landeck, L., Jakasa, I., Dapic, I., Kezic, S. and Danby, S.G., 2019. Epidermal tight junctions in atopic dermatitis and psoriasis. Acta Dermato-Venereologica, 99(1), pp.1–8.
5. Gulec, S., Collins, J.F. and Anderson, G.J., 2014. Mechanistic and regulatory aspects of intestinal iron absorption. Frontiers in Pharmacology, 5, p.156.
6. Kunstfeld, R., Rantou, C., Biedermann, T. and Luger, T., 2021. Marine omega-3 phospholipids and skin health: A review. Journal of Clinical and Aesthetic Dermatology, 14(3), pp.30–36.
7. American Academy of Dermatology Association, 2023. Thyroid disease and the skin. [online] Available at: aad.org [Accessed 19 May 2025].
8. Kubiak, K., et al., 2019. Vitamin D status and the skin barrier: Potential connections to psoriasis. Dermato-Endocrinology, 11(1), p.e1628069.