An allergic reaction to different types of allergens, drugs and food results in the release of histamine from mast cells. Histamine is an important mediator of the immune system that enters the surface of skin cells and causes irritation and inflammation. This acute or chronic inflammation is typically manifested in different types of skin rashes that may be involved with hives. If you suddenly develop an allergic reaction rash, try to identify the allergen, and avoid further contact. You can also apply a cool compress, and over-the-counter hydrocortisone cream to an itchy rash.
Allergic Contact Dermatitis
Allergic contact dermatitis occurs when your skin is directly exposed to substances such as soap, lotion, fragrance or cosmetics that trigger an immune reaction. The allergic reaction to the allergen is typically delayed, with a rash developing within 24 to 48 hours. Symptoms of an allergic contact dermatitis includes redness, tenderness or inflammation in the area of the skin exposed to the allergen, localized swelling in the exposed area of the skin, scaly and dry patches of the skin and a red rash. The rash may be accompanied by hives and may progress to lesions and blisters, and crusting in severe cases. The first line of treatment for contact dermatitis is identification of the allergen, and avoiding further contact. You may also apply a cool compress and hydrocortisone cream to the affected area to alleviate the itching and redness. In severe cases, you may experience swelling of the face, eyes and genitals, and should immediately seek medical help.
Maculopapular Rash
A skin rash is a common allergic reaction to antibiotics such as amoxicillin, cephalosporin, sulphonamide, and penicillin. This type of skin rash is typically accompanied by a headache and fever. It appears one to two weeks after beginning the medication, and begins as blotchy, red or pink, flat spots that appear on the trunk of the body and eventually spread to the neck and limbs in a symmetrical pattern. This rash typically resembles measles or rubella and is sometimes mistaken as a viral infection. Within a few days, the discreet red to pink flat spots begin to cluster and merge together, forming sheets of blotchy, flat rashes over the entire body. The first line of treatment is prompt discontinuation of the drug, which typically leads to resolution of the rash over one to two weeks.
Hives
An allergic reaction to foods, antibiotics, or an insect bite can cause the release of histamine from immune cells, resulting in swollen, blister-like itchy spots known as hives. The release of histamine into the surface layer of skin causes lesions, redness, and itching of the skin. These lesions typically appear within 24 hours of contact with the allergen and are often red in color, with pale, raised centers. The hives tend to migrate to different locations in the body, and in severe cases, may merge together and form large clusters of itchy, raised hives. The release of histamine into the deeper layers of the skin causes increased vascular permeability and swelling around the face, lips, eyelids, and genitals. Prompt discontinuation of the allergen is the first line of treatment, and second generation antihistamines may be prescribed to alleviate the itching and swelling.
Atopic Dermatitis
Atopic dermatitis, also known as eczema, is a common allergic reaction caused by hypersensitivity to an allergen on the skin. This results in chronic inflammation of the skin, and as a result, the skin becomes extremely dry and itchy, with red to brownish-gray patches throughout the body. These patches are typically small, raised bumps or blisters, that ooze fluid and crust over. The itching in the affected area of the skin is typically severe, and long-term scratching causes the skin to become leathery, cracked, and thick. Although these patches can occur anywhere on the body, they tend to localize behind the knees, in front of elbows, ankles, wrist, upper chest, neck and face. Your physician may recommend prescription corticosteroid creams, immunomodulators, antihistamines or antibiotics to prevent future flare up and reduce the inflammation.
References
- American Academy of Allergy, Asthma and Immunology: Allergic Skin Conditions
- The New York Times Health Guide; Allergic Reactions; September 3, 2011
- Medline Plus; Contact Dermatitis; November 2009
- DermNet NZ; Morbilliform Drug Reaction; Delwyn Dyall-Smith, MD
- Allergy Clinic; Urticaria, Hives, Nettle rash and Angioedema; Dr.Adrian Morris
- Mayo Clinic.com; Atopic Dermatitis (Eczema); April 2011
