Rashes are one of the most common reasons parents call a GP, NHS 111, or a health visitor in the first few years — and one of the most variable in what they actually mean. Some look terrifying and are completely benign. A few look unimpressive and matter quite a lot. The skill is knowing which features actually distinguish the worrying rash from the boring one.
This guide covers the most common rashes in babies and young children, what tells one apart from another, and — most importantly — the specific signs that mean you stop reading articles and pick up the phone.
Photographing the rash and logging when it appeared, where it started, and how it has spread in Healthbooq gives your GP or health visitor much more useful information than trying to recall the timeline at the appointment.
The Glass Test — The One Thing Every Parent Should Know
Before any specific rash, the single most important piece of rash knowledge: the glass test. Press the side of a clear glass tumbler firmly against the rash. If the rash fades (blanches) under the pressure of the glass, it is blanching — and the vast majority of rashes are. If the rash does not fade — if the red or purple spots remain visible through the glass — it is non-blanching, and in a child who is unwell, that combination is a medical emergency. Call 999.
Non-blanching rashes (petechiae and purpura) represent bleeding under the skin. The most feared cause is meningococcal disease. The child with meningococcal sepsis is typically very unwell: high fever, cold or mottled hands and feet, rapid breathing, severe leg pain, drowsiness or marked irritability. In babies, look for a high-pitched moaning cry, dislike of being handled, refusal to feed, a bulging fontanelle, and floppiness. The rash can start small — a few pinpricks on the legs or trunk — and spread fast.
Two practical points worth knowing:
- The rash can appear late in meningococcal disease. A very unwell child without a rash, or with only a small one, still warrants urgent assessment.
- Not every non-blanching rash is meningococcal — there are benign causes — but a non-blanching rash in any child who is unwell needs urgent assessment, not Google.
Do the glass test on any rash in a sick child. It takes ten seconds and gives you the most important piece of information you can get at home.
Nappy Rash
Nappy rash is contact dermatitis from prolonged exposure to urine and stool. It appears as redness in the nappy area, classically on the convex surfaces — buttocks, the inner thighs, the front of the genitals — but not the skin folds (which are protected from urine and stool by their geometry).
What helps: more frequent nappy changes, nappy-free time when practical, and a thick layer of a zinc-oxide barrier cream (Sudocrem, Metanium, Bepanthen) at every change. Avoid wipes if the skin is broken; use cotton wool and warm water.
When it is not simple nappy rash:
- The rash does involve the skin folds, with a bright red scalloped edge and small "satellite" spots beyond the main area → likely secondary Candida (thrush), which needs an antifungal cream in addition to barrier cream.
- The rash includes weeping, crusted, or honey-coloured scabby areas → possible bacterial infection (impetigo), which needs GP review.
- The rash is severe, blistering, or rapidly worsening despite barrier cream → GP review.
Heat Rash (Miliaria)
Tiny pink-red spots or clear fluid-filled tiny vesicles, usually on the neck, upper chest, face, or skin creases. It comes from blocked sweat glands when sweat cannot evaporate freely — typically in hot weather, in an overdressed baby, or when a baby has been swaddled or wrapped. It is not itchy, the baby is otherwise fine, and it resolves quickly once the baby is cooled and dressed appropriately. No specific treatment needed.
Roseola (Sixth Disease)
Caused by human herpesvirus 6. The pattern is distinctive once you know it:
- Three to five days of high fever — often 39–40°C — in a child who, despite the temperature, looks relatively well. (This is the bit that confuses parents and sometimes GPs.)
- The fever breaks.
- A pink, flat rash appears on the trunk and sometimes spreads to the limbs.
- The rash lasts one to two days and fades.
A child who seemed surprisingly hot but surprisingly well for several days and then develops a rash as the temperature comes down has, almost always, roseola. No treatment needed for the rash.
Slapped Cheek (Fifth Disease, Parvovirus B19)
A bright red rash on both cheeks — exactly as if the child has been slapped — often with a pale ring around the mouth that makes the contrast even more striking. A few days later, a lacy, net-like (reticular) rash appears on the body, arms, and legs. The child is usually only mildly unwell, with a low-grade fever and perhaps a cold-like illness.
Two important points:
- The rash phase is not the contagious phase. By the time the cheeks light up, the child has typically been infectious for the previous week and is now no longer infectious — they do not need to stay home from nursery once the rash appears.
- Parvovirus B19 can cause complications in pregnancy, particularly before 20 weeks (risk of foetal anaemia). Pregnant contacts who have not had it before should speak to their midwife if they have been around a confirmed case.
Hand, Foot and Mouth Disease
Coxsackievirus. Small grey-white blisters on the palms, soles, and inside the mouth, sometimes with non-blistering red spots on the buttocks and legs. The mouth blisters are the part that bothers the child most — they cause mouth pain that can affect feeding and lead to drooling. Hand, foot and mouth is highly contagious between children but resolves on its own in 7–10 days.
What helps: paracetamol or ibuprofen for the mouth pain, cold foods (ice lollies, cold yoghurt, cold smoothies), soft foods, and avoiding acidic or salty foods that sting. Encourage fluids — dehydration from refusal to swallow is the main complication.
Chickenpox
Itchy red spots that quickly develop a fluid-filled blister at the centre, then crust over. Crucially, spots appear in crops over 3–5 days, so at any moment a chickenpox rash will have spots at different stages — fresh red, blistered, and crusted — at the same time. That mixed-stages picture is one of the more reliable diagnostic clues.
Most children get through chickenpox uneventfully, though it is more uncomfortable than parents tend to expect. Calamine lotion, oral antihistamine for itch (chlorphenamine in suitable age groups), cool baths, and short fingernails (or scratch-mittens for younger children) help. Paracetamol for fever — avoid ibuprofen in chickenpox, because of an association with rare but serious soft tissue infection.
Children should stay off nursery or school until all spots have crusted over (typically 5–7 days from the first spot). Pregnant contacts who have not had chickenpox should speak to their midwife — there is post-exposure treatment available in some cases.
When chickenpox is more concerning: the child is significantly unwell, very high fever lingering after day three, the spots become very red, swollen, painful, or look secondarily infected, the child has a chronic condition or is immunocompromised, or the child is under 4 weeks old. Any of these warrant medical review.
When Any Rash Needs Same-Day Review
A short list, on top of the obvious 999 call for non-blanching rash + unwell child:
- The child is significantly unwell — drowsy, very irritable, refusing feeds, breathing fast.
- Fever above 38°C in a baby under 3 months, regardless of rash.
- The rash is rapidly spreading or becoming significantly more red, swollen, or hot.
- Painful, hot areas of skin (possible cellulitis or worse).
- Mouth ulcers severe enough to stop drinking — risk of dehydration.
- A rash you cannot identify and the child seems unwell with it.
Most rashes are not these. Most rashes are something the immune system is dealing with on its own, and your job is to keep the child comfortable, watch the trajectory, and call only when one of the specific flags appears. The glass test is the one piece of knowledge that turns the rest of this list into something you can manage at home.
Key Takeaways
Most rashes in babies and young children are viral, self-limiting, and resolve within days to two weeks without treatment. The single most important rash skill for any parent is the glass test: press a clear glass firmly against the rash, and if the spots do not fade under the pressure (non-blanching) and the child is unwell, that is a 999 call for possible meningococcal disease. The other commonly encountered rashes — nappy rash, heat rash, roseola, slapped cheek, hand-foot-and-mouth, and chickenpox — each have distinct features that, once you know what to look for, are easier to identify than the photos in any single Google Image search will suggest.
