Eczema isn’t something you catch. It develops from a combination of genetic vulnerability, an overactive immune system, and environmental exposures that together compromise your skin’s ability to hold moisture and keep irritants out. Most people with eczema (the most common form being atopic dermatitis) have some inherited predisposition, but genes alone don’t guarantee you’ll develop it. What tips the balance is usually a mix of triggers, timing, and how your skin and immune system interact from early life onward.
It Starts With a Faulty Skin Barrier
Healthy skin works like a brick wall: tough protein cells are the bricks, and a mix of fats (primarily ceramides) fills the gaps like mortar. In eczema, both components can be deficient. About 20 to 30 percent of people with atopic dermatitis carry a mutation in a gene called FLG, compared to just 8 to 10 percent of the general population. Roughly 40 different mutations have been identified so far. This gene provides instructions for making filaggrin, a protein that helps form the outermost layer of skin and keeps it hydrated. When filaggrin is deficient, the skin loses water too quickly and dries out, creating cracks that let allergens, bacteria, and chemical irritants slip through.
The fat component matters too. Research comparing eczema-prone skin to healthy skin found that a specific type of ceramide is significantly reduced in dry, eczematous patches, roughly half the level found in unaffected individuals. Without enough of these sealing fats, the skin barrier leaks. This is why eczema skin feels chronically dry even when you moisturize regularly: the underlying structure that holds water in place is compromised at a molecular level.
The Immune System Overreacts
A leaky skin barrier alone doesn’t fully explain eczema. The immune system plays an equally important role, and in many cases, the two problems feed each other in a loop. In people with eczema, a branch of the immune system responsible for fighting parasites and responding to allergens is dialed up too high. This overactive response produces inflammatory signals that cause redness, swelling, and intense itching. But those same signals also suppress the production of filaggrin and other barrier proteins, making the skin even leakier. So the immune response that’s trying to protect you actually makes the underlying barrier problem worse.
This is why eczema tends to flare and then partially improve in cycles. Something irritates the already-vulnerable skin, the immune system overreacts, inflammation damages the barrier further, more irritants get in, and the cycle continues until the trigger is removed or the inflammation is brought under control.
Bacteria on the Skin Play a Role
Everyone has bacteria living on their skin, but in eczema, the microbial balance shifts dramatically. A type of bacteria called Staphylococcus aureus colonizes the skin of nearly all people with atopic dermatitis. On healthy skin, a diverse mix of bacterial species keeps any single one in check. On eczema-prone skin, the broken barrier and altered immune environment let S. aureus dominate, and research has shown it actively drives eczema flares rather than just taking advantage of already-inflamed skin.
This is one reason eczema patches can sometimes look infected or weep fluid. The bacterial overgrowth triggers additional immune responses, adding to the inflammation already present and making flares harder to control.
Early Life Exposure Shapes Your Risk
Genetics loads the gun, but environment pulls the trigger. One of the most striking findings in eczema research involves children raised in different settings. A study comparing Amish children (raised on traditional farms with heavy microbial exposure), Swiss farm children, and Swiss non-farm children found dramatic differences: atopic eczema rates were 1.3 percent, 7.6 percent, and 12.1 percent, respectively. Children exposed to a wider range of microbes early in life developed immune systems that were better calibrated, less prone to the kind of overreaction that drives eczema.
This concept, sometimes called the hygiene hypothesis, suggests that the cleaner and more sterile a child’s early environment, the more likely their immune system is to misfire against harmless substances like dust, pollen, or pet dander. It doesn’t mean dirt prevents eczema, but diverse microbial exposure during the window when the immune system is still learning appears to help it develop tolerance rather than hypersensitivity.
What Triggers Flares Once You Have It
Once eczema is established, a wide range of everyday exposures can set off flares. These don’t cause eczema in the way a virus causes a cold. They aggravate skin that’s already predisposed. Common triggers include:
- Fabrics: Wool and synthetic blends are frequent offenders. Pure cotton or satin against the skin is far less irritating. If you need to wear a wool sweater, layering a cotton undershirt underneath can prevent direct contact.
- Fragrances and chemicals: Scented candles, perfumed soaps, and household cleaners often trigger flares on exposed areas like the face, neck, and hands. Clothing labeled “wrinkle free,” “shrink-resistant,” or “stain resistant” can contain chemical resins that provoke reactions.
- Environmental allergens: Dust mites, pollen, mold, and pet dander are classic triggers. Even seasonal decorations can carry enough dust or plant resin to set off a flare.
- Temperature and humidity: Very dry air pulls moisture from already-compromised skin. Sweating in hot conditions can also irritate, because sweat contains salts that sting broken skin.
Food Allergies Are Less of a Factor Than You’d Think
Many people assume specific foods cause eczema flares, and it’s one of the most common questions parents ask about children with the condition. The relationship is more complicated than it appears. While older studies suggested a strong link between food allergies and eczema, more recent research from the American Academy of Allergy, Asthma & Immunology tells a different story. In controlled studies, children whose only symptom was worsening eczema reacted to placebo foods just as often as to actual allergens, suggesting the connection was coincidental.
When foods do trigger eczema-like reactions, they almost always come with other symptoms: gastrointestinal issues, respiratory problems, or hives. An eczema flare as the sole symptom of a true food allergy is rare. This doesn’t mean no one with eczema reacts to food, but eliminating foods without testing often leads to unnecessary dietary restriction without improvement in the skin.
Types of Eczema Have Different Causes
Atopic dermatitis is the most common type, and it’s what most people mean when they say “eczema.” It tends to show up in early childhood, often on the face, inside the elbows, and behind the knees, and it’s the type most strongly linked to genetics and immune dysfunction.
Contact dermatitis is different. It happens when your skin touches something it’s allergic or sensitive to, like nickel in jewelry, latex, or a specific chemical in a cleaning product. Remove the substance and the reaction clears. Dyshidrotic eczema causes small, intensely itchy blisters on the palms and soles, and tends to worsen with stress or exposure to certain metals. Each type has its own primary driver, but they all share the core features of barrier disruption and immune-mediated inflammation.
Why Some People Get It and Others Don’t
The honest answer is that no single factor determines whether you develop eczema. Someone can carry filaggrin mutations and never have a single flare. Someone with no known genetic risk can develop it after prolonged exposure to harsh chemicals at work. What the research consistently shows is that eczema emerges from a collision of factors: inherited skin barrier weaknesses, an immune system prone to overreaction, bacterial imbalance on the skin’s surface, and environmental conditions that exploit those vulnerabilities. The more of these factors align, the more likely eczema becomes, and the harder it is to keep under control once it starts.