Drug rashes are a side effect of a drug that manifests as a skin reaction.
Drug rashes usually are caused by an allergic reaction to a drug, but some drug rashes are not allergic.
Typical symptoms include redness, bumps, blisters, hives, itching, and sometimes peeling, or pain.
Every drug a person takes may have to be stopped to figure out which one is causing the rash.
(See also Overview of Hypersensitivity and Reactive Skin Disorders.)
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 or cause no symptoms. Drugs can cause rashes in several ways.
Allergic drug rashes
Most drug rashes result from an allergic reaction to a drug. Usually the reaction is to a drug taken by mouth or by injection. The drug does not have to be applied to the skin to cause a drug rash. When the immune system comes into contact with a drug, it can become sensitive to that drug (a process called sensitization). Sometimes a person becomes sensitized to a drug after only one exposure, and other times sensitization occurs only after many exposures. Once a person is sensitized to a drug, later exposure to that drug triggers an allergic reaction, such as a rash.
Nonallergic drug rashes
Certain drugs make the skin particularly sensitive to the effects of sunlight or other sources of ultraviolet light (photosensitivity
Other rashes that result from drugs are those that occur in Stevens-Johnson syndrome, toxic epidermal necrolysis, and erythema nodosum.
Symptoms of Drug Rashes
Drug rashes vary in severity from mild redness with tiny bumps over a small area to peeling of the entire skin. Rashes may appear suddenly within minutes after a person takes a drug, or they may be delayed for hours, days, or even weeks. Rashes may cause red, purple, blue, or gray discoloration. Some rashes are painful and may cause sores to form in the mouth.
Photo courtesy of Anar Mikailov, MD, FAAD.
People with an allergic rash can have hives and/or other allergic symptoms, such as runny nose and watery eyes. They also may develop more significant symptoms such as wheezing or dangerously low blood pressure. Hives are very itchy, whereas some other drug rashes itch little, if at all.
Diagnosis of Drug Rashes
A doctor's review of all current prescription and over-the-counter drugs
Stop drugs most likely to have caused the reaction to see whether rash goes away
Sometimes skin biopsy
Figuring out whether a drug is responsible may be difficult because a rash can result from only a tiny amount of a drug, it can erupt long after a person has first taken a drug, and it can persist for weeks or months after a person has stopped a drug. Every drug a person has taken is suspect, including those bought without a prescription, such as eye drops, nose drops, suppositories, and herbal products, so doctors review all of the prescription and over-the-counter drugs a person is currently taking. Doctors try to determine whether the rash started shortly after a person began taking a drug. The drug most likely to be causing the rash will probably be stopped to see whether the rash goes away.
Sometimes the only way to determine which drug is causing a rash is to have the person stop taking all but life-sustaining drugs. Whenever possible, chemically unrelated drugs are substituted. If there are no such substitutes, the person starts taking the drugs again one at a time to see which one causes the reaction. However, this method can be hazardous if the person has had a severe allergic reaction to the drug.
Occasionally, doctors apply reaction-causing substances, known as allergens, to the skin (called patch testing), which may be helpful for diagnosis of certain rashes. Sometimes, a sample of skin is removed and examined under a microscope (called a skin biopsy), particularly if doctors suspect a person has one of the more severe or unusual drug reactions.
Treatment of Drug Rashes
Stopping the responsible drug
For mild reactions, sometimes antihistamines and corticosteroid creams to relieve itching
For severe reactions, sometimes drugs given intravenously and hospitalization
Most drug reactions disappear when the responsible drug is stopped.
Standard itching treatments, such as antihistamines by mouth and corticosteroid creams, are used as needed.
Severe allergic skin reactions, particularly those accompanied by serious symptoms such as wheezing or difficulty breathing (called anaphylaxis
