Common Allergic Rashes

By Daniel More, MD, About.com

This person has atopic dermatitis on the arms. Red, scaly plaques can be seen on the inside of the elbows. In adults, atopic dermatitis usually involves the body creases, or flexural areas.

There are many types of itchy skin rashes. However, not all rashes that itch are related to skin allergies. The following are the most common types of allergic skin rashes.

Atopic Dermatitis (Eczema)

Atopic dermatitis frequently occurs in young children, although may start in young adults, and can continue into adult life.

The rash of atopic dermatitis, often called eczema, occurs where a person scratches. In infancy, the rash occurs on the chest, cheeks and scalp, where the child is able to scratch. Older children and adult typically have the rash in the skin folds of the elbows and behind the knees, although may also occur on the face, neck, hands, feet and back.

The rash is red, often flakes or oozes, and has small blisters or bumps. There are often excoriations, or areas of broken skin, from aggressive scratching.

Urticaria (Hives) and Angioedema (Swelling)

Urticaria, commonly called hives, is an itchy rash that can occur at any age. This rash appears as raised red bumps of various shapes and sizes, and typically lasts for only minutes to hours. While it can be very itchy, a person will generally not excoriate (scratch to the point of breaking the skin and cause bleeding) themselves.

The swelling that sometimes goes along with urticaria is called angioedema, and often involves the lips, the eyes, and the hands and feet. Angioedema is usually not itchy or red, it tends to burn, sting or cause a tingling sensation. Severe swelling that blocks the ability to breathe can be dangerous and even life-threatening.

Contact Dermatitis

Contact dermatitis is caused from skin contact with a substance that causes a rash-like reaction. People react to a variety of chemicals, including cosmetics, hair dye, metals, topical medications and dental materials. An example of a contact dermatitis is a rash from poison ivy, which is an extremely itchy and appears as blisters that ooze and crust after contact with plants of the Toxicodendron family.

A contact dermatitis rash may look like atopic dermatitis, but the rash is typically located only in the area of contact with the offending chemical. Common locations include the face, especially the eyelids, neck, hands and feet. Contact dermatitis to metals, such as in jewelry or snaps/buttons/zippers on clothing, commonly occurs on the neck, wrists/hands, earlobes and at the waistline.

Itching Without a Rash

It is a relatively common problem for people to have itching without a rash being present. The medical term for itching is pruritus, and this symptoms can represent a skin problem, or even an internal disease within the body.

When the itching is limited to a certain area of the body, the most likely reason is a disease process limited to the skin. The area of the body that itches often gives a big clue as to the cause of the itching.

Pruritus the involves the entire body may still represent a disease of the skin, or may be caused by metabolic problems such as thyroid disease or iron deficiency. Many medications can cause itching, particularly pain medications like codeine and morphine.