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.
There are many skin changes that can occur with a rash, including: swellingwarmthblistersbumpscolor changesitchingpain
Skin can react or break out for many different reasons, ranging from allergic reactions to infections and even cancer.
There are many questions a healthcare professional needs to ask when someone complains of a rash: how long the rash has been presenthow the rash started and changed over timewhether or not the rash itcheswhether or not the person has a fever or chillswhether anyone the person knows has had a similar rashwhether the person has any allergieswhat medications the person is takingwhether the person has had similar or other rashes in the pastwhether 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.
There are many possible causes of a rash. One major category is infectious conditions. These include: ringwormLyme diseasesyphilismeasles chickenpoxscabiesroseolaimpetigogenital herpesherpes zosterRocky Mountain spotted feverKawasaki diseaseHand, and, foot, and mouth diseaseCat scratch diseaseGroup A strep infectionsStaphylococcal infectionsDiaper rashScarlet 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 materialsprimary skin diseases, such as acne, psoriasis, eczema, or rosacea, which often occur for unknown reasonsautoimmune disorders, such as systemic lupus erythematosus, scleroderma,, and ulcerative colitisother conditions and diseases, such as diabetes or pregnancyskin cancer or a cancer deeper in the body that causes a rashleukemia, a blood cancer inflammation of blood vessels, called vasculitis, in the skinpoor circulation, which commonly causes rashes in the lower legsreaction to various childhood vaccinations, such as the chickenpox vaccineheat or sun exposure
Other causes are also possible. Sometimes the cause is not found.
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.
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.
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.
In some cases, a rash illness is highly contagious and spread to others. In other cases, however, a rash poses no risk to others.
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.
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.
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.
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.
Cecil's Textbook of Medicine, 1996, Bennett et al.
Harrison's Principles of Internal Medicine, 1998, Fauci et al.