Skin rash: causes, red flags and when to get urgent help

A rash is a visible change in the skin: red, pink, purple, grey or darker patches, bumps, blisters, scales, crusts or spots, often with itching, stinging or soreness. The pattern, where it is on the body, how quickly it appeared, whether it itches and what else you feel are the key details. A rash that appears with a fever, with feeling very unwell or with swelling belongs in a different category from a dry, itchy patch that has been present for weeks.

Appearance varies by skin tone. The NHS notes for hives, shingles, scabies and impetigo that redness may be harder to see on brown and black skin, and that raised spots may be easier to feel than see. For eczema it describes skin that can be red, white, purple or grey, or lighter or darker than the surrounding skin depending on skin tone.

The table lists rashes described in NHS pages, with the features that help separate them. It is not a way to diagnose yourself; the aim is to show how much the accompanying details matter.

For meningitis, the NHS says the rash usually starts as small red pinpricks, spreads quickly and turns into red or purple blotches, that it does not fade when the side of a clear glass is pressed against it, and that not everyone with meningitis gets one. Other symptoms include a high temperature, very cold hands and feet, a stiff neck, severe worsening headache, eye pain in bright light, seizures, vomiting, confusion and being very sleepy or hard to wake. For sepsis in adults the NHS lists confusion or slurred speech, uncontrollable shivering, muscle pain, fast breathing, blue, pale or blotchy skin and a rash that does not fade when pressed.

For allergic reactions the NHS says to call 999 if lips, mouth, throat or tongue suddenly swell, you are breathing very fast or struggling to breathe, your throat feels tight or you struggle to swallow, skin, tongue or lips turn blue, grey or pale, you suddenly become confused, drowsy or dizzy, or someone faints and cannot be woken. For hives it advises an urgent GP appointment or 111 if they do not improve after 2 days, spread, keep coming back, come with a high temperature and feeling unwell, or come with swelling under the skin.

For children the NHS says to call 999 or go to A&E if a child is unwell with a rash and has a stiff neck, dislike of light, confusion or agitation, difficulty breathing, pale, blue, grey or blotchy skin, lips or tongue, sudden swelling of the lips, mouth, throat or tongue, a tight throat, or a rash that looks like small bruises or bleeding under the skin and does not fade under a glass. It says a child may be seriously unwell without a high temperature, and that parents should trust their judgement.

Shingles has its own warning signs: the NHS advises an urgent GP appointment or 111 if you are pregnant, the rash is on or near the eye or nose, you have changes to vision, you have a severely weakened immune system or you are 17 or younger. Starting medicine within 3 days of the rash appearing works best.

• A rash that does not fade under a glass, with fever, headache, stiff neck or drowsiness.

• A rash with swelling of lips, tongue or throat, wheeze or difficulty breathing.

• Rash with confusion, slurred speech, uncontrollable shivering or very fast breathing.

• A blistering rash on one side near the eye or nose, or with vision changes.

• Rash with high temperature in someone who has a weakened immune system or is pregnant.

• Widespread, painful, peeling or blistering skin, or rapidly spreading redness.

The clinician asks when the rash began, where, how it has changed, whether it itches or hurts, any fever or feeling unwell, new medicines, foods, cosmetics, plants, animals, travel, contact with others who are ill or itching, personal and family history of eczema, asthma or hay fever, and vaccination history. For contact dermatitis the NHS says a GP can try to identify the cause and refer to a dermatologist if the substance cannot be found or the rash is not responding.

Examination covers the distribution of the rash, the type of lesion, skin tone, the scalp, nails and mouth, lymph nodes and general condition, with temperature, pulse and breathing rate in anyone who seems unwell. The glass test is a quick bedside check.

Many rashes are diagnosed by looking. When the cause is unclear tests are chosen to fit: skin swabs for suspected infection, blood tests for infection, inflammation or allergy, patch testing for suspected contact allergy, a skin scraping for scabies or fungal infection, or a skin biopsy. The NHS says for hives that if they do not go away with treatment you may be referred to a dermatologist, and for contact dermatitis that a GP may refer for further tests.

If sepsis or meningitis is suspected, hospital tests and treatment begin urgently; the NHS says sepsis is treated in hospital with antibiotics, oxygen and fluids into a vein.

Advice depends on the cause. For hives the NHS says a pharmacist can advise on antihistamine treatment, and to tell the pharmacist about any long-term condition because antihistamines may not be suitable. For shingles it suggests paracetamol, keeping the rash clean and dry, loose clothing, a cool compress, and not letting dressings or plasters stick to the rash. For contact dermatitis it says a pharmacist can recommend emollients and that the key is identifying and avoiding the substance.

More broadly, avoiding scratching, wearing loose cotton clothing, avoiding new skin products until the cause is clear and noting any new foods, medicines or plants helps the clinician. If a rash begins soon after a new medicine, do not stop a prescribed medicine without advice, but do mention the rash promptly.

A pharmacist for common rashes such as hives, mild contact dermatitis, impetigo (from 12 months) and, for adults, early shingles; a GP for rashes that persist, recur, spread or trouble you; NHS 111 or an urgent GP appointment for the urgent features above; 999 or A&E for suspected meningitis, sepsis or anaphylaxis. A dermatologist sees rashes that are unclear, not responding to treatment or chronic, such as severe eczema and psoriasis.