Skin rash: causes, treatment and when to worry

A rash is any change in the color or texture of your skin: red patches, welts, bumps, blisters or dry, scaly skin. It can itch, burn or hurt. Most rashes are not serious and clear up with simple care or with treatment the doctor recommends.

The best clues to the cause are how it looks, where it started, when it began and whether it came with other symptoms, like a fever.

Flat white patches where the skin feels normal are usually not a rash: they can be vitiligo, and the doctor can tell it apart from other light patches.

Doctor online 24/7 for your rash: video doctor visits 24/7 — book online and choose your time right away. Every day, any time (Puerto Rico time).

The causes table on this page lists the usual ones. Some clues:

• Contact dermatitis: redness and itching where skin touched something, such as soaps, detergents, cosmetics, clothing dyes, latex or plants. See eczema and dermatitis.
• Eczema: red, dry, scaly, itchy skin that flares and settles.
• Pityriasis rosea: it starts with one larger pink, oval patch and, days later, smaller patches appear on the chest, back, arms and legs; it can itch and usually clears on its own in 4 to 8 weeks. See pityriasis rosea.
• Hives: if it is raised, itchy welts that move around, it is most likely hives; they can come from an allergy, a medicine or an infection.
• Heat rash: small red bumps or tiny blisters on the neck, chest or skin folds in heat and humidity. See heat rash.
• Shingles: pain, itching or tingling, then blisters in a stripe on one side of the body or face. See shingles.
• Impetigo: red sores that blister, ooze and form a honey-colored crust. See impetigo.
• Insect bites and reactions to a new medicine.

What people call a skin allergy is usually one of these four, and each is treated differently:

• Hives (urticaria): raised, red, itchy welts called hives; each welt fades within hours and new ones appear elsewhere. Hives are one of the most common forms of skin allergy, though they also come from infections, heat, cold or stress.
• Contact dermatitis: red, itchy skin, sometimes with small blisters, right where something touched it, such as a soap, fragrance, nickel in jewelry, latex or a plant; it usually appears 24 to 48 hours later. See contact dermatitis.
• Atopic dermatitis (eczema): dry, scaly, very itchy skin that flares and settles. It is common in people with allergies or asthma, although allergies do not cause it.
• Angioedema: deeper swelling under the skin, mostly of the eyelids and lips, often together with hives. If your lips, tongue or throat swell, or you have trouble breathing, call 911.

What to take for a skin allergy? For the itch of hives, allergy pills (antihistamines such as cetirizine or loratadine) usually help; for contact dermatitis, the key is avoiding what caused it and soothing the skin. The doctor sees you by video, tells you which one you have and, if appropriate, prescribes and we send your prescription to your pharmacy. Doctor online 24/7: book a visit.

Dengue can cause a fever with a rash, pain behind the eyes and bone or joint pain. If you have a rash with a fever, read our dengue warning signs guide and watch closely as the fever starts to fall. If dengue is possible, the CDC advises acetaminophen and no aspirin or ibuprofen. Visitors are at risk too.

Treatment depends on the cause, and the doctor explains what fits your case. Meanwhile, if the rash is mild and you have no warning signs:

• Wash with warm, not hot, water and a gentle cleanser. Do not scrub; pat dry.
• Leave the area open to the air as much as you can.
• Avoid whatever may have set it off: a new soap, fragrance, cream or plant.
• Calamine lotion can soothe contact dermatitis, and over-the-counter hydrocortisone cream can help many rashes.
• Try not to scratch; keep nails short.
• If the doctor needs to confirm a cause, for example with blood work, she gives you a lab order for a lab near you and reviews the results with you.

If you feel pain, burning or tingling on one side of your body and then blisters appear in a stripe, get checked promptly: antiviral treatment works best when started early. If shingles is on your face or near an eye, get care the same day, because it can affect your vision.

For your safety, call 911 if you are short of breath, your throat feels tight or your face is swelling. Go to the ER for a fever with purple or bruise-like spots that do not fade when you press a glass on them, or widespread blisters with peeling skin. More in when to go to the ER.

We see children of all ages. Kids tend to get different rashes: viral rashes, hand, foot and mouth disease, chickenpox, diaper rash or impetigo. Read rashes in children.