Physical Allergy

Physical Allergy 

Definition

Physical allergies are allergic reactions to cold, sunlight, heat, or minor injury.

Description

The immune system is designed to protect the body from harmful invaders such as germs. Occasionally, it goes awry and attacks harmless or mildly noxious agents, doing more harm than good. This event is termed allergy if the target is from the outside—like pollen or bee venom—and autoimmunity if it is caused by one of the body's own components.

The immune system usually responds only to certain kinds of chemicals, namely proteins. However, non-proteins can trigger the same sort of response, probably by altering a protein to make it look like a target. Physical allergy refers to reactions in which a protein is not the initial inciting agent.

Sometimes it takes a combination of elements to produce an allergic reaction. A classic example is drugs that are capable of sensitizing the skin to sunlight. The result is phototoxicity, which appears as an increased sensitivity to sunlight or as localized skin rashes on sun-exposed areas.

Causes and symptoms

When the inflammatory reaction involves deeper layers of the skin, urticaria becomes angioedema. The skin, especially the lips and eyelids, swells. The tongue, throat, and parts of the digestive tract may also be involved. Angioedema may be due to physical agents. Often the cause remains unknown.

Diagnosis

Visual examination of the symptoms usually diagnoses the reaction. Further skin tests and review of the patient's photosensitivity may reveal a cause.

Treatment

Removing the offending agent is the first step to treatment. If sun is involved, shade and sunscreens are necessary. The reaction can usually be controlled with epinephrine, antihistamines, or cortisone-like drugs. Urticaria may be treated with antihistamines such as diphenhydramine (Benadryl) or desloratadine (Clarinex). Clarinex is non-sedating, meaning it will not make patients drowsy. Itching can be controlled with cold packs or commercial topical agents that contain menthol, camphor, eucalyptus oil, aloe, antihistamines, or cortisone preparations.

Prognosis

If the causative agent has been diagnosed, avoidance of or protection against the allergen cures the allergy. Usually, allergies can be managed through treatment.

Resources

Periodicals

Kirn, F. Timothy. "Desloratadine Improves Urticaria in Clinical Setting." Skin & Allergy News September 2004: 41.

Key terms

Antihistamine — Drugs that block histamine, a major cause of itching.

Hemolysis — Destruction of red blood cells.

Inflammation — Heat, redness, swelling, and pain caused by an immune response.

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physical allergy

n.

Hypersensitivity caused by exposure to various physical factors such as heat, cold, light, or mechanical irritation.