Non-Blanching Rash = EmergencyPress a clear glass against a rash: if the spots do NOT fade (non-blanching), this may be meningococcal disease or vasculitis, call 999/911 immediately, especially with fever.
Common Rash Types
| Rash | Appearance | Common Cause |
|---|---|---|
| Urticaria (hives) | Raised, itchy wheals, comes and goes | Allergic reaction |
| Eczema | Dry, itchy, flexural, chronic | Atopic dermatitis |
| Psoriasis | Silvery plaques on elbows, knees, scalp | Autoimmune |
| Shingles | Unilateral dermatomal blisters | Herpes zoster (VZV) |
| Meningococcal | Non-blanching petechiae/purpura | Neisseria meningitidis |
| Lupus (SLE) | Butterfly malar rash across cheeks | Autoimmune |
| Drug reaction | Widespread maculopapular, symmetrical | Drug hypersensitivity |
| Cellulitis | Red, warm, spreading skin | Bacterial infection |
Photo Your RashRashes evolve quickly. Photograph it with a timestamp before it changes: useful for your GP, especially if it fades before your appointment.
How do I know if a rash is serious?
Red flags: non-blanching (glass test), accompanies high fever, spreads rapidly, causes facial swelling/breathing difficulty (anaphylaxis), is very painful, or appears after starting a new medication.
What is anaphylaxis?
A severe, life-threatening allergic reaction with hives, swelling, breathing difficulty, and low blood pressure. Treat with adrenaline (EpiPen) and call 999/911 immediately.
Can stress cause a rash?
Yes. Stress can trigger or worsen eczema, psoriasis, and urticaria. It activates the immune system in ways that worsen inflammatory skin conditions.
What causes shingles?
Shingles is a reactivation of the chickenpox virus (varicella-zoster) that lay dormant in nerve ganglia. It causes a painful, blistering rash in a band following one nerve's distribution.
Frequently Asked Questions
When does a rash need urgent medical attention?
Seek emergency care for a rash that does not fade when pressed with a glass (possible meningococcal infection), or a rash with fever, facial or tongue swelling, difficulty breathing, widespread blistering, or peeling skin.
What blood tests are used when investigating a rash?
Depending on the pattern, doctors may check a full blood count, inflammatory markers (CRP/ESR), liver and kidney function, and specific tests such as ANA for autoimmune causes or IgE for allergy.
Can medicines cause a rash?
Yes. Drug reactions are a common cause, typically appearing days to weeks after starting a new medicine. Any new rash after starting a medication should be reported to your doctor, particularly if it is widespread or associated with fever.
References
Sources cited on this page. PubMed links open the original abstract.
- Hay RJ, Johns NE, Williams HC, et al. The global burden of skin disease in 2010. J Invest Dermatol. 2014;134(6):1527–1534. PMID 24166134 · doi:10.1038/jid.2013.446
A clinical approach to classifying skin rashes
Skin rashes can overwhelm the non-specialist. A systematic descriptive approach narrows the differential diagnosis before any tests are ordered:
- Distribution: Is it localised (contact dermatitis, tinea) or generalised (viral exanthem, drug rash)? Does it follow dermatomes (shingles)? Is it on sun-exposed areas (photosensitivity, lupus malar rash)?
- Morphology: Macule (flat discolouration), papule (raised, under 5 mm), plaque (raised, over 5 mm), vesicle (blister under 5 mm), pustule (pus-filled), purpura (non-blanching – caused by blood outside vessels – always serious).
- Blanching: Press a glass against any red rash. If it blanches (turns white), it is caused by blood within vessels (most inflammatory rashes). If it does not blanch (purpura, petechiae), it indicates blood has leaked out – caused by vasculitis, thrombocytopenia, meningococcal septicaemia, or scurvy. Non-blanching rash is a medical emergency until meningococcal disease is excluded.
- Associated features: Fever + rash suggests infection (measles, scarlet fever, dengue, meningococcal) or drug reaction. Joint pain + rash suggests reactive arthritis, SLE, or viral arthritis.
Blood tests used in rash investigation
- FBC: Thrombocytopenia causes purpuric rashes; eosinophilia is found in drug reactions and parasitic infections; atypical lymphocytes in EBV (glandular fever).
- CRP and ESR: Raised in systemic inflammation – vasculitis, systemic lupus, adult Still's disease (high-spiking fever + salmon-coloured rash + arthritis).
- ANA and anti-dsDNA: Lupus classically causes a butterfly (malar) rash across the cheeks and nose, sparing the nasolabial folds – very different from rosacea, which it is frequently confused with.
- ANCA: Palpable purpura (painful raised non-blanching spots) on the lower legs suggests vasculitis – particularly IgA vasculitis (Henoch-Schönlein purpura) in children, or ANCA-associated vasculitis in adults.
- LFTs and hepatitis serology: Jaundice + rash; hepatitis B and C can cause urticaria, purpura, or lichen planus.
- Throat swab / ASO titre: Scarlet fever rash – a fine sandpaper-texture generalised rash following streptococcal pharyngitis – is confirmed by throat culture or elevated anti-streptolysin O (ASO) titre.
Related reading
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Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.