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rash
Overview
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?
There are many skin changes that can occur with a rash, including:
• 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
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