The vast majority of rashes — heat rash, contact dermatitis, eczema, viral exanthems — clear up on their own or with simple over-the-counter treatment. But a small number of rashes are signs of something genuinely dangerous: anaphylaxis, meningitis, sepsis, Stevens-Johnson syndrome. Knowing which red flags to look for can save a life. Run through the checklist below.
Call 999 / 911 immediately if you have:
- Difficulty breathing, wheezing, or feeling like your throat is closing
- Swelling of the face, lips, tongue, or eyes
- A non-blanching rash (purple/red spots that don't fade under glass) plus fever, headache, or stiff neck
- Widespread blistering, peeling, or skin coming off in sheets
- Confusion, fainting, or rapid heartbeat with the rash
The 9 Red-Flag Signs
Non-blanching purple/red spots (petechiae)
Tiny pinpoint spots that don't fade when you press a clear glass against them. Indicates bleeding under the skin — possible meningococcal sepsis. Emergency.
Fever above 38°C with the rash
Any rash plus high fever — particularly with neck stiffness, headache, light sensitivity, or vomiting — needs same-day assessment. Could be meningitis, sepsis, or a severe drug reaction.
Facial/throat swelling or breathing trouble
Anaphylaxis. Use an EpiPen if available and call emergency services immediately.
Rash spreading rapidly (within minutes to an hour)
Hives that quickly cover large areas of the body — especially after eating, taking medication, or an insect sting — can precede anaphylaxis.
Blistering, peeling, or skin sloughing
Large fluid-filled blisters or skin coming off in sheets can signal Stevens-Johnson syndrome or toxic epidermal necrolysis — a severe drug reaction. Same-day care.
Mucous-membrane involvement
Sores in the mouth, eyes, or genitals alongside the skin rash. Often paired with #5. Emergency.
Bullseye-shaped lesion
A circular rash with a darker centre and lighter ring around it can indicate Lyme disease (after a tick bite). See a GP within days for antibiotic treatment.
Rash that's painful (not just itchy)
Burning pain, deep ache, or pain that travels along a nerve line on one side of the body could indicate shingles, cellulitis, or necrotising fasciitis. See a doctor within 24 hours.
Persistent rash > 2 weeks
Any rash unchanged for 14+ days, even if mild, deserves a clinical look. Could be eczema, psoriasis, fungal infection, or rarely cutaneous lymphoma.
2-Minute Decision Tree: A&E, GP or Home Care?
Walk through these questions in order. Stop at the first "yes" — that's your route.
1. Any red-flag sign above? → A&E / 999 / 911 now
Trouble breathing, non-blanching spots, facial swelling, rapid spread, widespread blistering, confusion, or fever with stiff neck.
2. Painful rash, fever under 38.5°C, or bullseye lesion? → Same-day GP or urgent care
Shingles, cellulitis, early Lyme disease and many bacterial infections need prompt antibiotics or antivirals to limit damage.
3. Rash older than 2 weeks, or recurring? → Routine GP within 1–2 weeks
Likely eczema, psoriasis, fungal infection, contact dermatitis or chronic urticaria — all benefit from a prescription-strength plan.
4. None of the above? → Home care + AI check
Try the self-care plan further down. Run a free AI rash check to narrow down the likely cause and confirm there are no hidden red flags.
The Glass Test (Take 30 Seconds)
Press the side of a clear drinking glass firmly against the rash. Watch what happens to the spots:
✓ Spots fade (blanching)
Likely a normal rash from inflammation or allergy. Continue to monitor and treat as needed.
✗ Spots stay visible (non-blanching)
Medical emergency. Call 999/911 — especially if the person also has fever, headache, or feels unwell.
What a Serious Rash Looks Like (By Colour & Pattern)
Colour and pattern are some of the strongest clues to whether a rash is dangerous. Use these as a guide, not a diagnosis.
- Purple, dark red or "bruise-like" spots that don't blanch — possible meningococcal sepsis or platelet problem. Emergency.
- Bright red, hot, tender, spreading patch — possible cellulitis. Same-day GP or urgent care.
- Red rash with clear blisters following a nerve line on one side of the body — shingles. See a GP within 72 hours for antivirals.
- Bullseye/target lesion expanding over days — early Lyme disease after a tick bite. GP within a few days.
- Widespread red rash with peeling palms/soles — possible Stevens-Johnson syndrome, scarlet fever or toxic shock. Emergency.
- Itchy raised wheals that move around the body — urticaria (hives), usually allergic and not dangerous unless airway involved.
- Pink or skin-coloured fine rash on torso with mild fever — usually a viral exanthem. Home care unless red flags appear.
For a colour-specific breakdown, see red rash on skin causes and itchy rash causes.
Special Situations
Rash in children and babies
Babies under 3 months with any rash and fever need urgent assessment. In older children, apply the glass test and red-flag checklist exactly as above. Rashes that appear with a very unwell, drowsy or floppy child should never be "watched at home" — call 111 (UK) or your paediatrician immediately.
Rash in pregnancy
New widespread rashes during pregnancy (PUPPP, cholestasis-related itch, prurigo) should always be discussed with your midwife or GP, even when not painful — some are linked to liver function and need monitoring.
Rash after starting a new medication
Any rash that appears 7–14 days after starting a new drug — particularly antibiotics, antiepileptics, allopurinol or NSAIDs — should be reported to the prescriber that day. Drug rashes can progress from mild to Stevens-Johnson syndrome within hours.
Rash after sun or heat exposure
Usually heat rash, polymorphic light eruption or sunburn. Compare features in our guides on heat rash vs allergic rash and heat rash vs sun allergy.
Get an instant AI assessment
Upload a photo of your rash. Our AI ranks the most likely causes and flags any features that warrant urgent medical review.
Upload photo for AI analysis →When You Can Safely Wait and See
You can usually treat a rash at home if all of the following are true:
- ✓ No fever, breathing problems, or swelling
- ✓ The glass test is blanching
- ✓ The rash is itchy or mildly uncomfortable but not painful
- ✓ It's localised (not spreading rapidly)
- ✓ You can identify a likely trigger (heat, new product, insect bite)
Try a cool compress, an oral antihistamine (cetirizine 10 mg), and 1% hydrocortisone cream (avoid the face for more than 5 days). If the rash hasn't improved within 7 days, book a GP appointment.
How to Photograph a Rash for Your Doctor or AI Check
Whether you are using the free AI Dermatologist, a teledermatology service or simply showing your GP, photo quality changes the result.
- ✓ Use natural daylight; avoid flash and harsh overhead light
- ✓ Take one wide shot (showing the body area) and one close-up (15–20 cm away)
- ✓ Place a coin or ruler next to the rash for scale
- ✓ Take a fresh photo every 24–48 hours so change is visible
- ✓ Note temperature, symptoms and any new foods/medications alongside the photo
FAQ: Quick Answers
Is it normal for a rash to itch more at night?
Yes — cortisol levels drop overnight and skin temperature rises, both of which increase itch perception. Cool the skin and take a non-drowsy antihistamine in the evening.
Can stress cause a rash?
Yes. Stress can trigger hives, eczema flares, psoriasis flares and rosacea. The rash itself is real even if the trigger is psychological.
Should I pop blisters in a rash?
No. Intact blisters are sterile barriers; popping them increases infection risk and scarring. Cover loosely with a non-stick dressing.
How long does a viral rash last?
Most viral exanthems clear in 5–10 days. If a rash persists beyond 2 weeks, see our guide on rash that won't go away.