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Skin Rash: Identifying Common Types and Red Flags

Most rashes are benign and self-limiting, but a non-blanching purpuric rash with fever is a meningococcal emergency. Learn to tell the difference.

Written by Suman Konda, PharmD, Clinical Pharmacist · Editorial policy · Not medical advice

Last updated: · How we check our content

Most common cause
Eczema, contact dermatitis
Emergency rash
Non-blanching + fever
Test
Tumbler/glass test for purpura
Autoimmune rashes
Lupus, psoriasis, vasculitis
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

RashAppearanceCommon Cause
Urticaria (hives)Raised, itchy wheals, comes and goesAllergic reaction
EczemaDry, itchy, flexural, chronicAtopic dermatitis
PsoriasisSilvery plaques on elbows, knees, scalpAutoimmune
ShinglesUnilateral dermatomal blistersHerpes zoster (VZV)
MeningococcalNon-blanching petechiae/purpuraNeisseria meningitidis
Lupus (SLE)Butterfly malar rash across cheeksAutoimmune
Drug reactionWidespread maculopapular, symmetricalDrug hypersensitivity
CellulitisRed, warm, spreading skinBacterial 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.

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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.