What Makes Some Skin More Prone to Eczema? Meet the Filaggrin Gene

Atopic dermatitis is not simply sensitive skin that flares when it meets the wrong trigger. The condition has a structural explanation, and understanding it shifts the conversation from managing reactions to understanding why the barrier that should prevent them is compromised in the first place.

Filaggrin is a protein produced in the outermost layers of the skin. Its job is to help flatten and bind the dead skin cells that form the stratum corneum, the skin's outermost defensive layer, into a tight, organised structure. As filaggrin breaks down, it releases amino acids and their derivatives that draw water into the skin and maintain the slightly acidic pH that keeps harmful microbes in check. This process is not decorative. It is how the skin maintains its barrier function: keeping water in and irritants, allergens, and microbes out.

Loss-of-function mutations in the FLG gene, which codes for filaggrin, are among the strongest known genetic risk factors for atopic dermatitis. A person who carries one or two of these variants produces less functional filaggrin, sometimes none at all. The consequences follow directly from the protein's role. Without enough filaggrin, the stratum corneum is less tightly organised. The skin loses water more easily, this is measurable as elevated transepidermal water loss. The skin surface becomes more alkaline, which disrupts the enzymes that manage the barrier and allows Staphylococcus aureus, a bacterium found on most people's skin without issue, to colonise more readily. Allergens and irritants that a fully intact barrier would block can now penetrate to immune cells beneath. Those immune cells respond. That response is what produces the inflammation, itch, and redness of an atopic dermatitis flare.

This is why two people can use the same soap, wear the same fabric, or live in the same household, and only one develops eczema. The trigger is real, but it is acting on a barrier that was already structurally compromised. Removing the trigger reduces the insult, but it does not repair the underlying deficiency. This also explains the atopic march, the tendency for atopic dermatitis in early life to precede the development of food allergies, allergic rhinitis, and asthma in the same person. A leaky skin barrier is an early entry point for allergen sensitisation; the immune system encounters allergens through skin before it encounters them through the gut or airway, and it responds differently as a result. Not everyone with atopic dermatitis carries an FLG mutation, and not everyone with an FLG mutation develops atopic dermatitis, other genetic and environmental factors are involved. But the filaggrin pathway is the best-characterised mechanism connecting genetic risk to barrier dysfunction to immune activation.

Current treatment for atopic dermatitis is clinically managed and requires a dermatologist's assessment, because the condition varies significantly in severity, affected area, and response to therapy. Barrier repair, through emollients that replace some of what a filaggrin-deficient skin cannot produce, is a consistent part of management across severity levels, not because it is a cure but because it addresses the physical gap in the barrier. Topical anti-inflammatory treatments reduce the immune response once it is active. For moderate to severe disease, newer systemic options target specific parts of the immune signalling pathway that drives atopic inflammation. The choice between these approaches depends on clinical assessment. Self-treating atopic dermatitis, particularly with topical steroids without guidance, can suppress symptoms while masking secondary infection or causing skin thinning with prolonged use, both outcomes that complicate subsequent management. Anyone with persistent, recurring, or widespread skin inflammation should have it assessed rather than managed by trial and error at home.

The filaggrin story is illuminating but incomplete. A significant proportion of people with atopic dermatitis do not carry FLG mutations, which means other mechanisms, immune dysregulation, microbiome disruption, environmental exposures, are operating independently or alongside the barrier defect. Research into the condition continues to refine which pathways are primary and which are downstream consequences. What the filaggrin story does settle is the framing: atopic dermatitis is not an allergy to specific things, and it is not caused by washing too much or too little. It is a condition in which the skin's first line of defence is structurally altered, and everything that follows, the reactions, the infections, the itch, is a consequence of that alteration. Knowing this does not change what a flare feels like, but it changes what a treatment plan is actually trying to do.

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