Childhood eczema is caused by a combination of genetic predisposition, immune system overactivity, and environmental triggers that together compromise the skin’s protective barrier. It is not caused by any single factor, which is why it tends to run in families but doesn’t affect every child the same way. About 65% of children with eczema show signs in the first year of life, and 90% develop it before age five.
A Faulty Skin Barrier Starts the Problem
Healthy skin works like a brick wall: flat, tightly packed cells on the surface lock moisture in and keep irritants out. A protein called filaggrin is largely responsible for building that wall. It bundles structural proteins together, flattening and strengthening the outermost skin cells into a strong barrier. As filaggrin breaks down naturally, it also produces the skin’s “natural moisturizing factor,” a collection of molecules that keep skin hydrated and maintain its slightly acidic pH, which itself helps fight off bacteria.
Around 40 known mutations in the gene that codes for filaggrin have been identified in people with eczema. These mutations produce a shortened, defective version of the protein that can’t do its job. The result is a barrier full of gaps. Water escapes through the skin faster than normal, leaving it chronically dry. Irritants, allergens, and bacteria slip through those same gaps, triggering the inflammation that shows up as red, itchy patches. In children with darker skin tones, that redness can be more subtle, and the eczema may appear more as small bumps around hair follicles or patches of lighter or darker skin.
Genetics and Family History
Eczema has a strong hereditary component. Research estimates approximately a 75% chance of inheriting the condition when it runs in the family. The relevant genes aren’t limited to filaggrin. Children can also inherit immune system tendencies that make their bodies overreact to substances that wouldn’t bother most people. A parent doesn’t need to have eczema specifically to pass along risk. Asthma and hay fever share the same genetic family of conditions (called atopic diseases), so a child whose parent has seasonal allergies may still be at elevated risk for eczema.
An Overactive Immune Response
In children with eczema, the immune system treats minor skin exposures as serious threats. The inflammatory response is driven primarily by a branch of the immune system that also handles allergic reactions. In young children specifically, this response is more intense and complex than in adults, involving multiple inflammatory pathways simultaneously. One consequence of this immune overreaction is that the skin produces fewer of the natural antimicrobial compounds it normally uses to keep harmful bacteria in check, creating an opening for infection and further irritation.
This is why eczema is more than just dry skin. The immune system is actively inflaming the skin from within, which is what makes it itch so intensely and why moisturizer alone often isn’t enough to control flares.
Bacteria on the Skin Play a Role
Everyone’s skin hosts a community of bacteria, but in children with eczema, that community becomes unbalanced. A bacterium called Staphylococcus aureus, commonly known as staph, tends to take over on eczema-affected skin. Its dominance is both a consequence and a cause of worsening symptoms. The same immune signals that drive eczema inflammation also suppress the skin’s ability to fight off staph, so the bacteria thrive. As staph populations grow, skin inflammation gets worse, creating a cycle that can turn a mild flare into a severe one.
When staph populations decrease, skin inflammation consistently improves. This is one reason why pediatricians sometimes recommend dilute bleach baths or other antiseptic measures during flares.
Food Allergies and Eczema
The relationship between food allergies and eczema is real but often misunderstood. Having eczema significantly raises a child’s risk of developing food allergies. One-year-olds with eczema are 6 times more likely to have an egg allergy and 11 times more likely to have a peanut allergy than children without eczema. Among children with moderate to severe eczema, 91% show sensitivity to at least one common food allergen.
The most consistently implicated foods are cow’s milk, egg, and peanut, followed by wheat, soy, and fish. Overall, 20% of children with eczema are allergic to peanut, egg white, or sesame seed, compared to just 4% of children without eczema.
However, food allergies don’t cause eczema in most children. The current understanding is that the broken skin barrier itself may be what allows food proteins to enter the body through the skin, sensitizing the immune system and eventually producing a food allergy. In some children, eating a trigger food can worsen eczema flares, but eliminating foods without confirmed allergy testing rarely helps and can lead to nutritional problems.
Environmental and Product Triggers
While genetics and immune function set the stage, everyday exposures determine when and how badly eczema flares. Several categories of triggers are worth knowing about.
Fragrances and essential oils are among the most common culprits. They’re added to soaps, lotions, detergents, and wipes. Natural fragrances are equally likely to cause reactions as synthetic ones. Tea tree oil, despite its reputation as a natural remedy, can both irritate the skin and cause allergic reactions in children with eczema.
Common skincare ingredients can quietly fuel flares. Lanolin, derived from sheep’s wool and found in many popular moisturizers, causes allergic reactions in a subset of children with eczema. Cocamidopropyl betaine, a foaming agent marketed as “tear-free” in baby shampoos, can trigger contact dermatitis. Propylene glycol hides in moisturizers, prescription eczema creams, and even liquid antihistamines, meaning a child allergic to it could paradoxically flare when using the very products meant to treat their eczema.
Alcohol-based products (listed as ethanol on labels) sting, burn, and dry out sensitive skin. Retinoids, a class of vitamin A derivatives found in some skincare products, are irritating enough to trigger flares on their own. Even urea, often included in moisturizers for its hydrating properties, can irritate eczema-prone skin and damage its protective acid layer.
Where Eczema Appears Changes With Age
The underlying causes remain the same as a child grows, but the physical pattern shifts. In infants, eczema typically appears on the cheeks, trunk, and outer surfaces of the arms and legs. As children get older, it migrates to the creases: the insides of the elbows, the backs of the knees, and around the wrists and ankles. By the teenage years, the hands and feet become the most common sites. Patches typically appear as scaly, rough, or thickened skin with visible scratch marks. In children who have been scratching for a long time, the skin can become noticeably thicker and more textured, a change called lichenification.
There is no single test for eczema. Diagnosis is based on the pattern of symptoms: persistent itching, a chronic and relapsing course, the characteristic distribution for the child’s age, and a personal or family history of allergic conditions. Lab tests and biopsies are generally unnecessary unless another condition needs to be ruled out.