The immune system plays a vital role in maintaining the health of all the tissues of the body. The immune system reacts to invaders, such as microorganisms, foreign substances, or cancer cells, and triggers inflammation to attack these invaders. Usually the immune system reaction protects the body and aids healing. However, sometimes the immune system overreacts, or the reaction is misdirected at healthy tissues and causes intense inflammation and damage. These abnormal immune system responses are called hypersensitivity reactions. Some hypersensitivity reactions are called allergies, especially when they occur after exposure to substances that are usually harmless to most people.
Hypersensitivity reactions can involve the skin and cause disorders such as the following:
Skin can be involved in a variety of immune system reactions, many of which cause rashes. The word "rash" refers to changes in skin color (such as redness) and/or texture (such as bumps or swelling). Many rashes itch, such as those that often develop after an allergic reaction, but some rashes are painful and others cause no sensations.
Sometimes an immune reaction is triggered by an infection, substances a person touches or eats, or by a medication or illicit drug a person takes, but many times doctors do not know why the immune system reacts to produce a rash.
Some rashes occur mostly in children, whereas others almost always occur in adults.
Although many skin disorders are caused by the immune system's reaction, some are caused by things that directly affect the skin without involving the immune system. Things that can cause itching and/or rash include certain chemicals, ingredients in cosmetics, certain medications or illicit drugs, body fluids (sweat, urine), ultraviolet light, heat, cold, friction, and other things.
Diagnosis
A doctor's examination
Sometimes a biopsy
The diagnosis of most hypersensitivity and reactive skin disorders that cause a rash is based on the appearance of the rash. The cause of a rash often cannot be determined by blood tests, so they are not usually done.
However, persistent rashes, particularly those that do not improve with treatment, may lead the doctor to do a skin biopsy in which a small piece of the skin affected by the rash is removed with a blade for examination under a microscope.
Treatment
Depends on the cause
Treatment of hypersensitivity and reactive skin disorders depends on the cause if it can be identified.
Stopping a medication or avoiding exposure to a known irritant may be all that is needed.
Bacterial infections are treated with antibiotics, and viral infections may be treated with antiviral medications.
Other medications applied to the skin may be helpful, and others can be taken by mouth to relieve symptoms (for example, antihistamines for itching).
More severe hypersensitivity skin disorders may require treatment with corticosteroids or immunosuppressants that lessen the body's overactive immune response.
