Allergens are more subtle trigger factors. An allergen does not irritate, but may trigger an AD flare-up in those who have become allergic to it from prior exposure. Allergens are usually animal or vegetable proteins from foods, pollens, or pets. When people with AD are exposed to an irritant or allergen to which they are sensitive, inflammation-producing cells come into the skin. There, they release chemicals that cause itching and redness.
Further damage occurs when the person scratches and rubs the affected area.
All AD sufferers must avoid irritants, while those with known allergies should likewise avoid allergens. Detecting an allergic substance can be difficult, as discussed below. Food allergies can cause flare-ups. Diagnosing food allergies is extremely difficult. The surest way is to observe a worsening of eczema when a particular food is eaten.