Skin rash causes in adults and when to get help

You spotted it in the shower. A patch of red, slightly raised skin on your forearm that was not there yesterday, and now that you are looking properly there might be a second one starting near your elbow. It does not hurt. It itches just enough to be annoying, and you have already begun listing everything new you have touched this week.

Rashes are one of the most common reasons adults contact a doctor, and one of the hardest things to describe down a phone line. The word covers everything from a mild grumble at a new washing powder to something that needs attention today. What separates those two is rarely the exact shade of red. It is the pattern, the speed, and how you feel in yourself while it is happening.

Why skin reacts the way it does

Your skin has a small vocabulary and a lot to say with it. Irritation, allergy, infection, heat and viral illness all reach for the same few words: redness, swelling, bumps, itch. So the cause is usually worked out from the story around a rash rather than the rash itself. When did it start, what is new in your life, where did it appear first, and where has it gone since.

The patterns that turn up most often

• Contact reactions. The rash sits exactly where something touched you, which is the giveaway. A nickel watch back, hair dye, the strap of a new sandal, a plant you pulled up without gloves. The border often traces the shape of whatever caused it.
• Eczema flares. Dry, cracked, fiercely itchy skin in the same familiar places, usually inside the elbows, behind the knees, the hands, the eyelids. Cold weather, a change of soap, stress and too many hot showers all push it along.
• Hives. Raised weals that travel. Any single hive usually fades within a day, but fresh ones keep appearing elsewhere, so the rash seems to move around your body overnight. A recent virus, a new medicine or a food can set them off, and often nothing is ever identified.
• Heat and sweat rash. Tiny prickly bumps in skin folds, under a waistband or a bra strap, after a humid night or a long run in the wrong top.
• Viral rashes arrive with a temperature or a sore throat and tend to be widespread and fairly even.
• Fungal patches creep outwards slowly, with an edge that is scalier than the middle.

Plenty of rashes sit in more than one box. Eczema scratched open for a week can become infected, and then you have two problems stacked on each other. Infected skin behaves differently, which our page on bacterial skin infections and cellulitis explains.

Why the pattern matters more than one spot

A single dot on your shin tells a doctor almost nothing. The useful information is the shape of the whole thing. Is it symmetrical on both sides of your body, or only where your sleeve ends? Has it stayed the same size for three days, or doubled since breakfast? Speed is the most telling feature, because a rash that spreads in hours behaves very differently from one sitting still for a fortnight.

If a rash is visibly spreading while you watch it, or you feel genuinely unwell with it, stop trying to identify it and get seen instead.

Photographs make skin well suited to video

Most problems lose something over a video call. Skin is the exception, because a rash is visible, it holds still, and a camera sees more or less what a doctor in the room would see. A few things help:

• Shoot in daylight near a window, with no filter and no flash if you can avoid it.
• Take one wide photograph showing how far it extends, then one close up. Skin looks like a different problem at different distances.
• Put a coin or a fingertip beside it for scale.
• Photograph it again next day from the same angle, because a doctor comparing two images can tell whether it is settling or advancing, and that changes the advice.

What helps while you wait

Stop the most likely culprit first, even before you are sure you are right. If the rash appeared two days after you switched shower gel, go back to the old one. Keep the area cool, wear loose cotton over it, and use a plain unperfumed moisturiser generously, because dry skin itches more. A pharmacist can advise on an antihistamine if the itching is keeping you awake. One thing to avoid is a half used tube of something strong left over from a previous problem, since creams that suit one rash can make another considerably worse. Our page on rashes and allergic skin reactions is worth reading alongside this.

When to get urgent help

• A rash that does not fade when you press on it. Press a clear glass firmly against the skin, and if the marks are still visible through the glass, treat it as an emergency.
• A rash with a fever, or with feeling very unwell, drowsy, confused, or unusually cold in the hands and feet.
• Any swelling of the lips, tongue, face or throat, a tight chest, a wheeze, or difficulty breathing or swallowing.
• Blistering, skin peeling away, or sores in the mouth, eyes or genitals.
• Redness that is spreading quickly and becoming hot and painful.
• A rash that starts within days of beginning a new medicine.

Call 999 for a rash that does not fade under pressure, for any breathing difficulty or swelling of the throat, or if someone is seriously unwell. For anything urgent that is clearly not an emergency, 111 is open day and night and will tell you where to go. If your rash is none of the above but has outstayed its welcome, you can arrange an appointment online instead of waiting to see what it does next.

How an online appointment works for a rash

You book a slot and a UK registered doctor sees you by video. They will want the timeline as much as the picture: when it started, what it has done since, what you have tried, and which medicines you take. Where treatment is needed the doctor can prescribe it if that is clinically appropriate, and can write a referral letter if your skin needs a dermatologist instead. Our guide to booking and joining an appointment covers the practical side, and every consultation is listed on the page showing what an appointment costs.

Worth saying plainly: an antibiotic does nothing for eczema, hives or a viral rash, because none of those are bacterial. Asking for one is understandable, but treatment has to match the cause. You can see the full list of problems our doctors deal with on the page covering the conditions we treat, and because allergic skin and allergic airways often travel together, some people also look at ongoing asthma and respiratory care.

Reducing the chance of the next one

If the same rash keeps returning, treat it as information. Write down the date, what you had used, eaten or worn, and where it appeared first, because two or three entries often reveal a pattern that a single episode hides. Fragrance free soap and detergent are a sensible default for reactive skin, gloves make washing up far less hostile to your hands, and testing a new product on a patch of inner arm first saves a fortnight of itching.

Skin problems are also easy to put off, because they are rarely dramatic and never convenient. If yours has been going for more than a week or two, keeps coming back, or is stopping you sleeping, book a video consultation about your rash and get a real answer instead of another late night image search.