What a rash is and how it looks
A rash is any visible change in the skin: redness, patches, small bumps, blisters or flaking. It can itch, hurt or cause no discomfort at all. The same-looking rash can come from an allergy or from an infection, so no one can diagnose it from a photo or a description. It needs an exam.
Doctors usually ask a few things: where the rash started and how it spread, whether it itches, whether there is a fever, and what you ate, took or touched in the last few days. It helps to think through the same questions before the visit.
Rash in a child
Children get rashes more often than adults, and most are viral or allergic. Chickenpox, measles and rubella all come with a rash, and an unvaccinated child is at higher risk. Flat pink spots that appear after a few days of fever, just as the temperature drops, are often a harmless viral rash, but only a pediatrician can say so.
One rash is different: spots that do not fade under pressure. If you press a clear glass against the skin, or stretch the skin, and the marks stay dark, call 112 right away. Meningococcal disease can look like this, and waiting is not safe.
Rash with a fever
If a rash appears together with a fever, chills, headache or unusual drowsiness, look at how the person feels overall, not only at the skin. Measles, rubella and chickenpox cause a rash in combination with a high temperature. An adult with a high fever and a spreading rash, and a child even more so, should be seen the same day. For the fever itself, see Fever.
Itchy rash and allergies
When a rash itches, the cause is often an allergy or dermatitis. Hives look like raised welts that come and go within hours. Contact dermatitis shows up where the skin touched something: a cleaning product, jewelry, cosmetics, a plant. Rashes with intense itching are covered on the Itching page.
If the lips, face or tongue swell, or breathing becomes hard, this is a severe allergic reaction: call 112.
Rash after a medication, sun or a new product
A rash can be a reaction to a drug, most often in the first days after starting it, to sun, heat and sweat, or to a new cream, shampoo or detergent. If a medication may be the cause, do not stop or change it on your own; call the doctor who prescribed it as soon as you can. If it followed a walk in the sun or a new product, stop using it and watch the skin.
What you can do before the visit
- Do not pop blisters or pick off crusts. It makes infection easier.
- Do not put alcohol, dyes or home-made ointments on the rash. They hide what the doctor needs to see.
- Wear loose cotton clothing and wash with lukewarm water and a gentle cleanser.
- Take a photo in daylight now and again later, so the doctor can see how it changed.
- Write down what you ate, which medications you took and whom you were in contact with.
How a doctor finds the cause
A dermatologist examines the skin, may look at it through a dermatoscope, and asks about contacts and medications. If an allergy is suspected, an allergist may add blood tests or skin tests. For a child with a rash and a fever, a pediatrician usually starts and decides whether tests or an infectious disease specialist are needed. Treatment depends entirely on the cause: an allergic rash and an infectious rash are treated very differently.