Eczema is a chronic inflammatory skin condition where the skin’s protective barrier doesn’t work properly, allowing moisture to escape and irritants to get in. It affects 10% to 20% of children and 2% to 10% of adults worldwide, making it one of the most common skin conditions on the planet. In the U.S. alone, roughly 31.6 million people have some form of it.
But “what exactly is eczema” is a fair question, because it’s more complex than just dry, itchy skin. It involves a specific breakdown in skin biology, an overactive immune response, and a bacterial imbalance that all feed into each other.
How the Skin Barrier Breaks Down
Healthy skin works like a brick wall. Skin cells are the bricks, and a mix of fats and proteins act as the mortar holding everything together. One protein in particular, called filaggrin, is essential for building strong skin cells and keeping the outer layer of skin hydrated and slightly acidic. That slight acidity matters because it keeps harmful bacteria in check and helps skin enzymes function normally.
In eczema, filaggrin production is reduced. Without enough of it, the skin loses moisture faster and its pH rises, becoming less acidic. That shift in pH sets off a chain reaction: it activates enzymes that further damage the skin barrier, which then triggers immune signaling molecules that launch an inflammatory response. The inflammation itself suppresses filaggrin production even more, creating a cycle where the barrier keeps getting weaker and the skin keeps getting more inflamed.
This is why eczema tends to be persistent. It’s not just a surface-level rash. The underlying biology locks the skin into a repeating loop of damage, inflammation, and more damage.
Why the Immune System Overreacts
Eczema isn’t just a skin problem. It’s also an immune system problem. When the weakened skin barrier lets in allergens, bacteria, or chemical irritants, the outer skin cells release alarm signals. Those signals activate a specific branch of the immune system designed to fight parasites and respond to allergens.
This immune response floods the skin with inflammatory molecules. Two of the most important ones drive much of what you experience as eczema: one promotes allergic-type inflammation and ramps up antibody production (which is why many people with eczema also have elevated allergy markers in their blood), while the other directly affects the skin tissue itself, making it more reactive and disrupted. Together, they cause the redness, swelling, and skin breakdown that define a flare.
A separate inflammatory molecule acts directly on nerve endings in the skin to cause itching. This is why eczema itch feels different from, say, a mosquito bite. It’s driven by a specific signal from immune cells to sensory neurons, and it can be intense enough to disrupt sleep and daily life.
The Role of Bacteria on the Skin
Everyone’s skin hosts a community of bacteria, but in eczema, a particular species called Staphylococcus aureus tends to take over. People with more severe eczema are the most likely to carry high levels of this bacterium, and its numbers spike during flares.
S. aureus doesn’t just sit on the skin passively. It produces toxins that punch holes in skin cells, damage the connections holding the barrier together, and trigger further inflammation. It also releases enzymes that break down skin proteins and, notably, interact with nerve cells to trigger itching. So the bacterium actively makes eczema worse by attacking the barrier, stoking inflammation, and intensifying the itch, all of which leads to more scratching, more barrier damage, and a more hospitable environment for the bacteria to thrive.
What Eczema Looks and Feels Like
Eczema doesn’t look the same at every stage. In its acute phase, the skin develops red, inflamed rashes that may contain small fluid-filled bumps. These can weep (leak clear fluid) and then crust over. This is the stage most people associate with a flare-up, and it’s often intensely itchy.
In a subacute phase, the inflammation is milder. You’ll typically see raised bumps, some swelling, and skin that’s dry and scaly but not actively weeping.
When eczema becomes chronic, the skin changes in a more lasting way. Repeated cycles of inflammation and scratching cause the skin to thicken and develop a leathery texture. This thickening, called lichenification, is the skin’s attempt to protect itself from ongoing irritation. Chronic patches tend to be less red but more visibly textured, and they can persist even between active flares.
On lighter skin, eczema usually appears pink or red. On darker skin tones, it often looks brown, purple, or grayish, which can make it harder to recognize.
What Triggers Flares
The underlying biology of eczema is always present, but flares are typically set off by specific triggers. These vary from person to person, but common ones include:
- Dry air and cold weather, which strip moisture from already-compromised skin
- Soaps, detergents, and fragrances, which dissolve the skin’s protective fats
- Sweat and heat, which irritate inflamed skin
- Allergens like dust mites, pet dander, and pollen
- Stress, which amplifies the immune response
- Certain fabrics, particularly wool and synthetic materials that trap heat
Research from the National Institute of Allergy and Infectious Diseases has also identified a class of industrial chemicals called diisocyanates as an eczema trigger. These chemicals are used to make polyurethane products like foams, coatings, adhesives, and sealants. The reactive part of the molecule also shows up in wildfire smoke, cigarette smoke, and automobile exhaust, which may partly explain why air pollution worsens eczema for some people.
Types of Eczema
Eczema is actually an umbrella term covering several related conditions. The most common by far is atopic dermatitis, which is the type driven by the immune and barrier dysfunction described above. It typically starts in childhood and runs in families alongside asthma and hay fever.
Contact dermatitis is the second most recognized type. It occurs when the skin reacts to a specific substance, either an irritant (like harsh chemicals) or an allergen (like nickel or poison ivy). Unlike atopic dermatitis, it tends to cause more of a burning sensation and stays localized to the area that touched the trigger.
Other forms include dyshidrotic eczema, which produces small, deep blisters on the hands and feet; nummular eczema, which appears as coin-shaped patches; and seborrheic dermatitis, which affects oily areas like the scalp and face. Each type has its own pattern, but they all share the core feature of a disrupted skin barrier and an overactive inflammatory response.
Why It’s Chronic but Manageable
There’s no cure for eczema, but that statement is more nuanced than it sounds. Many children with atopic dermatitis outgrow it or see significant improvement by adolescence. For adults who continue to have it, the condition tends to follow a pattern of flares and remissions rather than being constant.
Management centers on two goals: repairing the skin barrier and controlling the immune overreaction. Daily moisturizing with thick creams or ointments (not lotions, which are too thin) helps compensate for the barrier deficiency. Identifying and avoiding personal triggers reduces how often flares happen. When flares do occur, treatments range from topical anti-inflammatory creams to newer targeted therapies that block the specific immune signals driving the inflammation and itch. The newer treatments were designed around the exact immune pathways involved in eczema, which is why they tend to be more effective and have fewer side effects than older, broader approaches.
Understanding that eczema is a biological condition, not just sensitive skin or poor hygiene, changes how you approach it. The itch-scratch cycle, the bacterial overgrowth, the immune flare, and the barrier breakdown are all interconnected. Addressing any one of those pieces helps interrupt the cycle that keeps eczema going.