A rash is a change of the human skin that affects its color, appearance, or texture.
A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracked or blistered, swell, and may be painful.
The causes, and therefore treatments for rashes, vary widely. Diagnosis must take into account such things as the appearance of the rash, other symptoms, what the patient may have been exposed to, occupation, and occurrence in family members. The diagnosis may confirm any number of conditions.
The presence of a rash may aid diagnosis; associated signs and symptoms are diagnostic of certain diseases. For example, the rash in measles is an erythematous, morbilliform, maculopapular rash that begins a few days after the fever starts. It classically starts at the head, and spreads downwards.
Common causes of rashes include:
Food allergy
Medication side effects
Anxiety
Allergies, for example to food, dyes, medicines, insect stings, metals such as zinc or nickel; such rashes are often called hives.
Skin contact with an irritant
Fungal infection, such as ringworm
Balsam of Peru
Skin diseases such as eczema or acne
Exposure to sun (sunburn) or heat
Friction due to chafing of the skin
Irritation such as caused by abrasives impregnated in clothing rubbing the skin. The cloth itself may be abrasive enough for some people
Secondary syphilis
Poor personal hygiene
Uncommon causes:
Autoimmune disorders such as psoriasis
Lead poisoning
Pregnancy
Repeated scratching on a particular spot
Lyme disease
Scarlet fever
COVID-19 (see )
The causes of a rash are numerous, which may make the evaluation of a rash extremely difficult. An accurate evaluation by a provider may only be made in the context of a thorough history, i.e. medications the patient is taking, the patient's occupation, where the patient has been and complete physical examination.
Points typically noted in the examination include:
The appearance: e.g.