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A rash is an area of the skin that has broken out, usually with patches of redness, bumps, or blisters. It may affect any area of skin from one small patch to the entire body.

What is going on in the body?

• swelling
• warmth
• blisters
• bumps
• color changes
• itching
• pain

Skin can react or break out for many different reasons, ranging from allergic reactions to infections and even cancer.

What are the signs and symptoms of the condition?

There are many questions a healthcare professional needs to ask when someone complains of a rash:

• how long the rash has been present
• how the rash started and changed over time
• whether or not the rash itches
• whether or not the person has a fever or chills
• whether anyone the person knows has had a similar rash
• whether the person has any allergies
• what medications the person is taking
• whether the person has had similar or other rashes in the past
• whether the person has had a recent insect or tick bite

The healthcare professional may also ask about other symptoms, which can help narrow the list of possible causes. For instance, a person may be asked about his or her sexual history or whether he or she has had arthritis or weight loss.

What are the causes and risks of the condition?

There are many possible causes of a rash. One major category is infectious conditions. These include:

• ringworm
• Lyme disease
• syphilis
• measles
• chickenpox
• scabies
• roseola
• impetigo
• genital herpes
• herpes zoster
• Rocky Mountain spotted fever
• Kawasaki disease
• Hand, and, foot, and mouth disease
• Cat scratch disease
• Group A strep infections
• Staphylococcal infections
• Diaper rash
• Scarlet fever

These infections are all different from one another in terms of age groups at risk, exposure histories, time course of the rash, appearance of the rash, and other associated symptoms. Most often, these can be diagnosed on the basis of a history and physical exam. Sometimes, laboratory tests are required.

Other categories of rash illness include:

• allergic reactions, which can be from medications, metals, chemicals, soaps, lotions, foods, or other materials
• primary skin diseases, such as acne, psoriasis, eczema, or rosacea, which often occur for unknown reasons
• autoimmune disorders, such as systemic lupus erythematosus, scleroderma,, and ulcerative colitis
• other conditions and diseases, such as diabetes or pregnancy
• skin cancer or a cancer deeper in the body that causes a rash
• leukemia, a blood cancer
• inflammation of blood vessels, called vasculitis, in the skin
• poor circulation, which commonly causes rashes in the lower legs
• reaction to various childhood vaccinations, such as the chickenpox vaccine
• heat or sun exposure

Other causes are also possible. Sometimes the cause is not found.

What can be done to prevent the condition?

Prevention of a rash depends on the cause, which is sometimes difficult to diagnose. Those with allergies should avoid the substances they are allergic to whenever possible. Routine childhood vaccines can prevent some infections that cause a skin rash, such as measles and chickenpox. Avoiding the sun and using sunscreen can reduce the risk of skin cancer.

How is the condition diagnosed?

The cause of some rashes can be diagnosed after a history and examination of the rash. Other rashes, particularly from non-infectious causes, may be more difficult to identify. Further tests may be needed, including blood or urine tests. Sometimes, a biopsy of the affected skin is needed. This involves removing a small piece of skin with a special tool. The skin can then be analyzed in the lab to help determine the cause. Further tests may be needed in some cases, depending on the suspected cause. For instance, the healthcare professional may order a chest X-ray if he or she suspects that a lung infection is causing the rash.

What are the long-term effects of the condition?

Some rashes, such as severe acne, may cause permanent scarring of the skin. Other rashes may become infected because of skin breakdown. In very rare cases, such as with severe allergic skin reactions, rashes can even result in death.

For most rashes, the long-term effects are related to the underlying cause. For instance, cancer or serious infections that cause rashes may result in death. Rashes associated with pregnancy often go away after delivery and have no long-term effects.

What are the risks to others?

In some cases, a rash illness is highly contagious and spread to others. In other cases, however, a rash poses no risk to others.

What are the treatments for the condition?

Affected skin should be kept clean, especially if there is skin breakdown. Specific treatment depends on the cause. For instance, those with infections may need antibiotic pills or creams applied to the rash. Those with allergic reactions may need antihistamines or corticosteroid pills or creams. Those with autoimmune disorders may need medications to suppress the immune system. Those with cancer or poor circulation may need surgery.

What are the side effects of the treatments?

Medications may cause allergic reactions, stomach upset, and headaches. Specific side effects depend on the medications used. For instance, antihistamines often cause drowsiness. Surgery can be complicated by bleeding, infection, or reactions to anesthesia.

What happens after treatment for the condition?

If the rash goes away, an individual may or may not need further treatment. For instance, those with diabetes or poor circulation need further treatment and monitoring even after their rashes go away. Those who have ringworm, a fungal infection of the skin, are cured after treatment. They can return to normal activities without further treatment.

How is the condition monitored?

People can monitor their own rashes at home. Those with skin breakdown need to watch for infection until the skin heals over. The healthcare professional may also want to monitor the rash periodically, depending on the cause. Any new or worsening symptoms should be reported to the healthcare professional.