Dry skin, eczema and psoriasis: what your biomarkers might reveal

Immune dysregulation and systemic inflammation

Both eczema and psoriasis involve abnormal immune activity, though through different pathways. In atopic eczema, the immune system overreacts to environmental triggers, producing elevated IgE antibodies and eosinophils that drive itching, redness and barrier breakdown. In psoriasis, autoreactive T cells trigger an inflammatory cascade that accelerates skin cell turnover from the usual 28-30 days down to 3-5 days, resulting in the characteristic scaling plaques. In both cases, systemic inflammation markers such as CRP (C-reactive protein) are often elevated, and raised CRP in psoriasis is consistently associated with more severe symptoms and higher risk of cardiovascular and metabolic comorbidities. Measuring these inflammatory markers provides visibility into what is happening systemically, not just at the skin surface.

Nutrient deficiencies affecting the skin barrier

The skin barrier depends on specific micronutrients to maintain its integrity and modulate the immune response. Vitamin D plays a direct regulatory role in skin immune function, and low levels have been linked to increased severity of both eczema and psoriasis in multiple studies. A 2024 meta-analysis found that vitamin D supplementation was associated with reduced atopic dermatitis severity in children and adults with confirmed deficiency. Vitamin B12 supports skin cell turnover and immune regulation, and research suggests it may help reduce psoriasis symptoms. Iron and ferritin are required for cellular repair and oxygen delivery to the skin; low ferritin contributes to poor healing and is commonly depleted alongside inflammatory skin conditions. Zinc plays a role in skin integrity and wound repair, and deficiency can exacerbate inflammatory skin responses. Testing these nutrient co-factors alongside inflammation markers provides a complete picture of what is and is not supporting your skin from within.

Gut microbiome dysregulation and the gut-skin axis

There is substantial and growing evidence connecting gut health to skin conditions, particularly eczema. The gut microbiome plays a central role in immune education and systemic inflammation regulation. Dysbiosis (an imbalance of gut bacterial populations) increases intestinal permeability, allowing bacterial fragments and inflammatory molecules to enter the bloodstream and amplify immune reactivity throughout the body, including at the skin. People with eczema frequently show distinct differences in gut microbiome composition compared to unaffected individuals. Histamine-producing bacteria in the gut can also drive histamine intolerance, which manifests as skin flushing, itching and eczema-like flares that are often misattributed to food allergy. Understanding your gut microbiome profile alongside blood biomarkers gives a more complete picture of why your skin is reacting the way it is.

Thyroid dysfunction and hormonal factors

Thyroid disorders and skin conditions overlap more frequently than standard testing reveals. Hypothyroidism and Hashimoto's thyroiditis are both associated with persistent dry, flaky skin, impaired wound healing and changes in skin texture, because thyroid hormone regulates the rate at which skin cells are produced and shed. Psoriasis and eczema also carry a higher rate of co-occurring autoimmune thyroid disease, since underlying immune dysregulation tends to affect multiple systems simultaneously. If you experience fatigue, weight changes or mood shifts alongside skin symptoms, checking thyroid markers alongside inflammation and nutrient panels provides a much more informative starting point than skin-only assessment.

Genetic predisposition and filaggrin variants

A significant proportion of people with eczema carry variants in the filaggrin gene (FLG), which encodes a structural protein essential to the skin barrier. FLG loss-of-function variants are among the strongest known genetic risk factors for atopic dermatitis, and they also increase susceptibility to food allergy and asthma through what is known as the atopic march. Psoriasis has a strong hereditary component, with multiple chromosomal loci, including PSORS1, identified as major genetic determinants. DNA-level testing can identify whether genetic predisposition to inflammatory skin conditions or barrier dysfunction is part of your picture, which changes how you approach both prevention and long-term management.

Stress, cortisol and the HPA-skin axis

Chronic stress elevates cortisol, which disrupts the immune balance that keeps both eczema and psoriasis in check. Elevated cortisol suppresses regulatory immune responses while amplifying inflammatory ones, a pattern that consistently predicts flare frequency in both conditions. Stress is one of the most commonly reported triggers for psoriasis flares, and the mechanism is directly biological rather than simply psychological. This is why skin condition management that focuses only on topical treatment without addressing systemic inflammation, nutrient status and stress physiology tends to produce partial and inconsistent results.

Standard GP assessment for eczema and psoriasis is clinical, based on symptom presentation and history. Blood testing is typically only initiated when symptoms are severe, when standard treatments have not worked, or when systemic medication is being considered. This means that the internal factors driving skin symptoms, including vitamin D status, ferritin, thyroid function, inflammation levels and gut health, are rarely investigated in people with mild to moderate persistent skin conditions.

A more comprehensive approach looks at the systemic factors that most commonly underlie or amplify inflammatory skin conditions:

CRP (C-reactive protein) measures systemic inflammation. Elevated CRP in people with skin conditions is both a signal of disease activity and a risk factor for the cardiovascular and metabolic complications associated with psoriasis.

Vitamin D is directly involved in immune regulation at the skin level. Low vitamin D is consistently associated with greater eczema and psoriasis severity, and is highly prevalent in the UK population due to limited sunlight availability for most of the year.

Ferritin is an iron storage marker that affects tissue repair and immune function. Low ferritin impairs the cellular machinery needed to repair a compromised skin barrier and is frequently depleted in people with chronic inflammatory conditions.

Vitamin B12 supports immune regulation and skin cell turnover. Research indicates a potential role in reducing psoriasis activity, and deficiency is common in people with gut absorption issues, which frequently co-occur with eczema.

CRP and homocysteine together give insight into both acute inflammation and longer-term cardiovascular risk, which is elevated in psoriasis due to the sustained systemic inflammatory burden the condition places on the body.

Gut microbiome assessment identifies dysbiosis, reduced diversity, histamine-producing bacteria, and imbalances in the short-chain fatty acid-producing bacteria that regulate systemic immune responses. This layer of information is not available from blood testing alone and is particularly relevant for people whose skin symptoms are accompanied by digestive issues.

For people whose skin symptoms have been assessed clinically but have not responded fully to topical treatments, comprehensive blood and microbiome testing often reveals modifiable factors that standard dermatology assessment does not capture.

Nutrition for the skin barrier and immune regulation

Vitamin D from sunlight is limited in the UK for most of the year, and dietary sources (oily fish, eggs, fortified foods) rarely provide sufficient intake alone. Monitoring your vitamin D level and supplementing based on your actual measurement is more reliable than estimating from sun exposure or diet. Omega-3 fatty acids from oily fish, walnuts and flaxseed reduce the inflammatory signalling that drives eczema and psoriasis flares. Iron-rich foods support ferritin levels and barrier repair. Probiotic and prebiotic foods (fermented vegetables, legumes, diverse fibre sources) support the gut microbial diversity that regulates systemic immune responses. Tracking these biomarkers over time is the only reliable way to know whether your dietary approach is working at the biological level.

Gut health and its relationship to skin

Reducing processed food intake, increasing dietary fibre variety and incorporating fermented foods consistently improves microbial diversity in most people. If gut symptoms (bloating, irregular bowel habits, food sensitivities) accompany skin symptoms, assessing your microbiome provides targeted information that general dietary advice cannot. People with a confirmed dysbiosis pattern benefit from knowing specifically which bacterial populations are imbalanced, rather than applying a one-size-fits-all probiotic approach.

Managing systemic inflammation through lifestyle

Chronic psychological stress, disrupted sleep and excessive alcohol intake all raise systemic inflammation and trigger or worsen skin flares. Regular low-intensity exercise has been shown to reduce inflammatory markers including CRP over time. Consistent sleep timing supports immune regulation at a circadian level. These factors are not incidental to skin health, they are direct biological inputs into the immune dysregulation driving eczema and psoriasis. Testing CRP at baseline and retesting after sustained lifestyle changes is the most direct way to track whether your inflammation is actually reducing.

Long-term tracking over single snapshots

Inflammatory skin conditions fluctuate with season, stress cycles, hormonal changes and gut health status. A single test provides a baseline; repeated testing over time reveals the patterns that predict your flares and the changes that are genuinely moving the needle. This is the difference between guessing at triggers and actually understanding your biology.