Causes of Eczema: Genetics, Immune System, and Triggers

Eczema develops from a combination of genetic, immune system, and environmental factors rather than a single cause. A key piece is a weakened skin barrier — often tied to specific gene variations — that lets moisture escape too easily and allows irritants, allergens, and bacteria to penetrate the skin more readily, triggering inflammation.

Researchers don't fully understand every detail of why eczema develops, but the general picture has become much clearer in recent years, particularly around genetics and the skin barrier.

Genetics: a strong and well-documented factor

Eczema, and atopic dermatitis specifically, has a significant genetic and hereditary component. You're more likely to develop eczema if there's a family history of eczema or dermatitis, and the risk increases further with a family history of asthma, hay fever, or other allergic conditions. Research has identified several genes involved in eczema's development, most notably the filaggrin (FLG) gene, which plays a critical role in maintaining the skin's barrier function.

Research supported by the National Institutes of Health has also identified specific variations in a gene called KIF3A that impair the skin barrier and increase water loss from the skin, which promotes the development of atopic dermatitis. This kind of genetic research is significant because it opens the door to identifying infants who may be at higher risk before symptoms even appear.

The skin barrier connection

A healthy skin barrier keeps moisture in and keeps irritants, allergens, and bacteria out. In people with eczema, genetic variations — including those affecting the filaggrin gene — impair this barrier function, allowing increased water loss and easier penetration by outside substances. This is a central mechanism behind eczema: the skin becomes both drier and more reactive than typical skin, which sets the stage for the itching, inflammation, and rash that characterize the condition.

People with a weakened skin barrier are also more prone to skin infections, including from a bacterium called Staphylococcus aureus, which tends to be present at higher levels on eczema-affected skin and may contribute to ongoing inflammation.

Immune system activity

Beyond the physical skin barrier, the immune system plays an active role in eczema. People with eczema have an overactive immune response to environmental triggers, which leads to the inflammation and skin damage seen during flares. In atopic dermatitis specifically, certain immune cells become abnormally activated, promoting production of antibodies linked to allergic disease and worsening the same barrier problems caused by genetic factors — creating something of a cycle between immune activity and barrier dysfunction.

This immune component is also why eczema is often discussed alongside other allergic conditions. Eczema, asthma, and allergic rhinitis (hay fever) are sometimes grouped together as the "atopic march," reflecting how often these conditions appear together in the same person over time. A substantial proportion of people with severe eczema go on to develop asthma or allergic rhinitis as well.

Environmental triggers

Genetics and immune activity set up the underlying susceptibility, but environmental exposures often trigger or worsen individual flares. Common triggers include:

Irritants such as soaps, detergents, and disinfectants that directly disrupt the skin barrier.
Allergens including pollen, pet dander, dust mites, mold, and certain foods.
Climate and lifestyle factors, including dry air, excessive hand-washing, or reduced early-life exposure to certain microbes, which some research links to the broader rise in eczema rates over recent decades.

Eczema is also notably more common in urban areas than rural ones, a pattern that researchers connect to broader lifestyle and environmental differences, though the exact mechanisms are still being studied.

Why eczema has become more common

Genetic causes alone don't explain how quickly eczema rates have risen over the past several decades. Researchers point to environmental and lifestyle shifts — including reduced early immune-system stimulation in increasingly hygienic environments — as a likely contributing factor alongside genetics, though this remains an active area of research rather than a fully settled explanation.

What this means for managing eczema

Because eczema arises from an interaction between genetics, immune activity, and environment, no single intervention addresses all of it. This is part of why eczema management generally combines skin barrier support (moisturizing routines), avoidance of individual triggers once identified, and, for more significant cases, medical treatment aimed at calming immune system activity. Understanding your own likely mix of genetic risk and environmental triggers can help make a treatment plan more targeted rather than generic.

FAQ

Is eczema purely genetic, or can anyone develop it?
Genetics is a major factor, but eczema develops from a combination of genetic predisposition, immune system activity, and environmental triggers — it isn't caused by genetics alone, and people without a strong family history can still develop it.

Why does eczema run in families?
Several genes, including the filaggrin gene, affect the skin's barrier function and immune response, and variations in these genes are inherited. A family history of eczema, asthma, or allergies significantly raises the risk.

What role does the skin barrier play in eczema?
A weakened skin barrier, often linked to genetic factors, allows more moisture to escape and lets irritants, allergens, and bacteria penetrate more easily — a central mechanism behind eczema's itching and inflammation.

Can environmental factors cause eczema even without a genetic risk? Environmental triggers like irritants, allergens, and dry climates primarily worsen or trigger flares in people already predisposed to eczema, rather than independently causing the condition in someone with no underlying susceptibility.

Why is eczema more common now than in past decades?
Genetics can't fully explain the rapid rise in eczema rates in recent decades. Researchers believe environmental and lifestyle changes, including reduced early immune-system stimulation, are likely contributing alongside genetic factors.

Practical takeaway

Eczema comes from genetics, immune activity, and environment working together, which is why identifying your personal triggers — while also supporting your skin barrier with consistent moisturizing — tends to matter more than searching for one single "cause" to eliminate. If flares are frequent or severe despite basic trigger avoidance and skin care, a doctor can help identify which piece of the underlying picture needs more targeted treatment.