Allergic Disease & Asthma Center

Although allergic skin reactions are very common, it is often difficult to determine what causes them. Irritated skin can be caused by a variety of factors. These include immune system disorders, medications and infections. When an allergen is responsible for triggering an immune system response, then it is an allergic skin condition.

Eczema (Atopic Dermatitis)
Eczema, or atopic dermatitis is extremely common, especially in children. It is thought to be caused by a defect in the skin barrier, which causes skin to dry out and become irritated and inflamed. Some food sensitivities can make eczema symptoms worse. Eczema is often linked with asthma, allergic rhinitis (hay fever), or food allergy. You are more likely to develop eczema if a parent has any of the above conditions. Unlike with urticaria (hives), the itch of eczema is not caused by histamine, so anti-histamines will not control the symptoms.
Hives (Urticaria)
When your immune system releases histamine, small blood vessels leak, which leads to swelling and inflammation of the skin, or hives. Swelling in deep layers of the skin is called angioedema.

There are two kinds of urticaria, acute and chronic. Acute urticaria occurs after eating a particular food or coming in contact with a particular trigger such as heat or exercise, as well as medications, foods, or insect bites. Chronic urticaria can last for many months or even years.
Allergic Contact Dermatitis
When your skin breaks out in a rash after direct contact with an allergen, it’s called allergic contact dermatitis. For example, many people have allergies to nickel, which is often in belt buckles, jewelry, and even iPads! They may develop a red, bumpy, itchy, or swollen rash at the place of contact.

Plants such as poison ivy, poison oak, and poison sumac also cause allergic contact dermatitis. These plants are covered with an oil that causes an itchy, red rash.
Angioedema/Swelling
Angiodema is often seen with hives, and occurs when there is swelling and inflammation in the deep layers of the skin. Angioedema many times occurs in soft tissues such as the eyelids, mouth or genitals.