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What to do if…
you develop a new rash that is spreading quickly

Short answer

A new rash that’s spreading quickly is urgent. Call 999 now if there are danger signs (breathing/swallowing problems, swelling of lips/tongue/face, severe illness, or a rash that does not fade under pressure). Otherwise, get same-day medical advice via NHS 111.

Do not do these things

Do not “wait it out” if the rash is spreading quickly or you feel unwell.
Do not try a new cream/ointment, essential oil, or antibiotic cream “to see if it helps” (it can worsen irritation or hide important clues).
Do not take your next dose of a recently started or recently changed medicine until you’ve had urgent advice, unless a clinician has told you it must not be missed. If you have blistering/peeling skin or sores in the mouth/eyes/genitals, treat this as an emergency and seek urgent hospital care.
Do not scratch or vigorously rub the rash (it can break the skin and worsen inflammation).
Do not go straight into a crowded waiting room if you also have fever/cough/runny nose and a new rash—phone first so you can be seen safely.

What to do now

Check for emergency danger signs (act immediately if any apply). Call 999 (or go to A&E) now if you have any of these:
- Trouble breathing, wheezing, throat tightness, or trouble swallowing
- Rapid swelling of lips, tongue, face, or throat
- Feeling faint, very dizzy, suddenly confused, or unusually drowsy
- A rapidly worsening rash with severe illness, severe headache with a stiff neck, seizures, or you feel “seriously unwell”
- Blisters/peeling skin, or sores in the mouth/eyes/genitals, or widespread skin pain
If you have signs of a severe allergic reaction and you carry an adrenaline auto-injector, use it now as directed, and call 999.
Do a quick “glass test” if the rash includes purple/red spots. Press the side of a clear glass firmly against the rash:
- If the spots do not fade, treat this as an emergency and call 999.
If no danger signs, contact NHS 111 for same-day guidance. Say clearly: “I have a new rash that is spreading quickly,” and mention any fever, pain, pregnancy, immune problems, or if it’s in a child.
Write down what changed recently (this helps triage). Note:
- When it started and how fast it’s spreading
- Any recently started or changed medicines (days to weeks), including over-the-counter tablets (pain relievers/cold remedies), supplements, and herbal products
- New foods, insect stings/bites, new detergents/skin products, recent infections, or close contact with illness
Take clear photos now and track the edge.
- Photograph the rash in good light (wide shot + close-up).
- If it’s expanding across a patch, gently mark the edge with a washable pen and note the time.
Use the safest comfort steps while you arrange help.
- Keep cool (heat can worsen itch). Loose clothing, cool compresses.
- If it’s itchy and you can normally take them, consider an over-the-counter non-drowsy antihistamine and follow the pack directions. Ask a pharmacist first if you’re pregnant/breastfeeding, the rash is in a child, or you take other medicines. Avoid drowsy products if you may need to travel/drive.

What can wait

You do not need to figure out the exact cause right now.
You do not need to start restrictive diets, stop multiple long-term medicines, or do “detox” plans in a panic.
You can postpone allergy testing, changing all household products, and deep-cleaning until you’ve had medical advice.

Important reassurance

Many rashes are treatable and not dangerous, but “new + spreading quickly” is a sensible reason to get same-day advice. Taking a few calm, specific steps now helps clinicians act quickly if this is something that needs urgent treatment.

Scope note

This is first-steps guidance for the next minutes to hours. Once you’re assessed, next actions depend on the rash pattern, your symptoms, and recent exposures/medicines.

Important note

This is general information, not a diagnosis. If you are severely unwell, the rash is rapidly spreading, or you have any emergency warning signs, seek urgent medical care immediately.

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What to do if…you develop a new rash that is spreading quickly