Atopic dermatitis isn’t something you catch. It develops from a combination of genetic predisposition, immune system behavior, and environmental exposures that together compromise your skin’s ability to function as a barrier. About 12.7% of children in the United States have been diagnosed with it, and while it often starts in infancy or early childhood, it can appear for the first time at any age.
Genetics Set the Stage
The single strongest genetic risk factor is a mutation in the gene responsible for producing a protein called filaggrin, which plays a critical role in forming and maintaining the outer layer of your skin. When this gene doesn’t work properly, your skin can’t build a strong barrier. Water escapes more easily (even from skin that looks perfectly normal), and irritants and allergens get in more readily. Between 10% and 40% of people with atopic dermatitis carry at least one of these mutations, and the more severe someone’s eczema is, the more likely they are to have one.
But genetics alone don’t explain the whole picture. Many people with filaggrin mutations never develop atopic dermatitis, and many people with atopic dermatitis have perfectly normal filaggrin genes. What the genetic component does is lower the threshold, making it easier for other factors to tip the balance.
Family history matters broadly, too. If one or both of your parents have atopic dermatitis, asthma, or hay fever, your risk goes up substantially. These conditions tend to cluster in families because they share overlapping immune tendencies.
An Overactive Immune Response
In atopic dermatitis, the immune system leans heavily toward a type of inflammatory response that’s normally reserved for fighting parasites. Certain immune cells in the skin produce signaling molecules, particularly IL-4, IL-13, and IL-31, that ramp up inflammation and itching. This is the same branch of the immune system involved in allergic reactions, which is why atopic dermatitis often coexists with other allergic conditions.
Here’s what makes it self-reinforcing: those same inflammatory signals actively suppress production of filaggrin and other proteins your skin needs to maintain its barrier. So even if you started with normal filaggrin genes, chronic inflammation can reduce your skin’s barrier function over time. The weakened barrier lets in more irritants, which triggers more inflammation, which further weakens the barrier. This cycle is a core reason atopic dermatitis tends to flare and persist rather than simply resolving on its own.
In people who’ve had atopic dermatitis for a long time, additional types of immune cells join the response, further suppressing barrier proteins and making the condition harder to control without treatment.
Your Skin’s Lipid Layer Breaks Down
Healthy skin relies on a thin layer of fats, including ceramides, cholesterol, and fatty acids, packed tightly between the outermost skin cells. Think of it like mortar between bricks. In atopic dermatitis, all three of these key lipids are reduced. The inflammatory signals mentioned above directly suppress the enzymes and proteins your skin needs to produce and organize these fats. The fatty acids that are produced tend to be shorter than normal, which means they don’t pack together as tightly.
On top of that, the skin’s pH tends to be higher than normal in atopic dermatitis, which delays the processing of lipids after they’re released. The net result is a barrier full of gaps: moisture escapes, the skin dries out, and environmental irritants pass through easily.
Environmental Triggers and Risk Factors
Genes and immune tendencies create vulnerability, but environmental factors often determine whether and when the disease actually shows up.
Climate is one of the clearest influences. A large Japanese study tracking children from birth found that low humidity (specifically low vapor pressure) was the strongest climate-related predictor of developing atopic dermatitis by age three, increasing risk by about 26%. Cold temperatures showed a similar association. Dry, cold air pulls moisture from the skin and stresses an already compromised barrier.
Air pollution is another well-documented trigger. Tobacco smoke, volatile organic compounds (found in paints, cleaning products, and new furniture), formaldehyde, nitrogen dioxide from traffic exhaust, and particulate matter all act as risk factors for developing or worsening atopic dermatitis. These pollutants appear to cause oxidative damage in the skin, disrupting barrier function and triggering immune reactions. Indoor air quality matters as much as outdoor: urbanization and tightly sealed buildings concentrate these exposures.
Common day-to-day triggers include harsh soaps and detergents, wool and synthetic fabrics against the skin, sudden temperature changes, sweating, and psychological stress. These don’t cause atopic dermatitis on their own, but in someone with the underlying predisposition, they can provoke or worsen flares.
Early Microbial Exposure Plays a Role
Children raised in environments with greater microbial diversity, think farms, households with pets, or larger families, tend to have lower rates of atopic dermatitis and other allergic conditions. The underlying idea, sometimes called the hygiene hypothesis, is that early exposure to a wide range of microbes helps train the immune system toward balanced responses rather than the allergy-prone pattern seen in atopic dermatitis.
Greater diversity of gut bacteria in early life, particularly early colonization with certain beneficial species, is associated with stronger signals from the branch of the immune system that counterbalances allergic inflammation. Children with less microbial diversity in their gut tend to show weaker development of this counterbalancing response, leaving the allergy-prone pathway relatively unchecked. This helps explain why atopic dermatitis rates have climbed alongside increased sanitation, antibiotic use, and urban living.
The Connection to Other Allergic Conditions
Atopic dermatitis is often the first stop in a progression sometimes called the atopic march. Children who develop eczema early in life have a higher risk of going on to develop food allergies, asthma, and hay fever. In one large cohort study, about 36% of people with a history of atopic dermatitis reported having asthma at some point.
The likely mechanism ties back to the broken skin barrier. When the skin can’t keep allergens out, immune cells in the skin encounter food proteins, pollen, and pet dander directly. This sensitizes the immune system through the skin rather than through the gut or airways, where tolerance is more likely to develop. It’s one reason why early and consistent treatment of the skin barrier in infants with eczema is an area of active clinical focus.
Who Gets It and When
Atopic dermatitis affects boys and girls at similar rates: about 12.2% and 13.3%, respectively, among U.S. children. Prevalence is fairly consistent across age groups in childhood, hovering between roughly 12% and 14%. Living in a city versus a rural area doesn’t appear to make a significant difference in the U.S., with rates of about 12.8% in metropolitan areas and 12.5% outside them.
Most cases begin before age five, and many children improve significantly by adolescence. But atopic dermatitis can also start in adulthood, and a meaningful number of people carry it throughout their lives. Adult-onset cases sometimes look different clinically, with less of the classic crease-of-the-elbow pattern and more involvement of the hands and face.
There’s no single cause of atopic dermatitis. It emerges when a genetically susceptible person encounters enough environmental pressure, whether that’s dry air, irritant exposure, microbial imbalance, or some combination, to push their skin barrier and immune system past a tipping point. Understanding which factors are at play for you can help guide which management strategies are most likely to help.