What counts as a high temperature?

Body temperature normally sits between roughly 36.5C and 37.5C, though it drifts slightly during the day and varies a little between people. A reading of 38C or above is generally treated as a high temperature, or fever, in both adults and children.

Fever is a symptom rather than an illness in itself. It is the body's normal response to infection, and in most cases it means the immune system is doing exactly what it should. The vast majority of fevers are caused by common viral infections that settle within three to five days.

Use a reliable digital thermometer and take the reading the same way each time. In young babies, an armpit reading is usually the most practical, and ear thermometers are not suitable for babies under four weeks old. If the number does not match how unwell the person seems, always go by how they look and behave rather than the reading alone.

When to contact your GP surgery

Many fevers can be safely managed at home with rest and fluids. Contact your GP surgery for advice if any of the following apply:

• A temperature of 38C or above lasting more than three days, or one that keeps returning after it settles
• A fever that does not come down at all with age-appropriate paracetamol or ibuprofen
• Other symptoms such as a sore throat that makes swallowing difficult, ear pain, a worsening cough, or pain when passing urine
• Vomiting or diarrhoea that is not settling, or any signs of dehydration
• A new rash, or any symptom you cannot explain
• Pregnancy, a long-term condition such as diabetes, heart or lung disease, or a weakened immune system
• Recent travel abroad, especially to a country where malaria is present
• An adult temperature above 39.5C, or someone who feels very unwell despite the fever coming down

It is also worth a call if someone seems to be improving and then suddenly gets worse again, or if you are simply worried and cannot settle. Nobody will mind you checking.

Signs you need urgent care or should call 999

Some symptoms mean you should not wait for a routine appointment. Call 999 or go to your nearest A&E if someone with a high temperature has any of the following:

• Difficulty breathing, breathing very fast, or grunting noises when breathing
• Lips, tongue, face or skin that look pale, blue or grey, or skin that appears mottled
• A stiff neck, a severe headache, or dislike of bright lights
• Confusion, drowsiness that is hard to rouse them from, or a sudden change in behaviour
• A rash that does not fade when you press a clear glass against it
• A fit or seizure
• Signs of severe dehydration — no urine for 12 hours, sunken eyes, no tears when crying, a dry mouth
• Being floppy, limp or unresponsive

These can be signs of serious infection, including sepsis or meningitis, and they need assessing straight away. If you cannot get to A&E safely, call 999.

High temperatures in babies and young children

Age matters a great deal here, and thresholds are lower for the youngest babies.

• Under three months: a temperature of 38C or above is urgent. Call 111 or take your baby to A&E the same day, even if they seem otherwise well.
• Three to six months: a temperature of 39C or above should be discussed with a clinician urgently.
• Any age: a fever alongside a non-blanching rash, breathing difficulty, or unusual floppiness needs emergency assessment.

Children often run higher temperatures than adults and can look quite unwell with a minor illness, then perk up once the fever breaks. A child who is drinking, passing urine and interested in what is going on around them is usually reassuring. A child who is listless, refusing fluids, or not responding to you is not.

Looking after someone with a high temperature at home

• Offer plenty of fluids — water, milk or oral rehydration solution. Small, frequent sips are often better than one large glass.
• Give paracetamol or ibuprofen at the dose recommended for their age or weight. Do not give both at once as a matter of routine, and always follow the instructions on the packet.
• Dress them in light clothing and keep the room comfortably cool. Do not wrap them up to "sweat it out".
• Do not sponge with cold water — it can make things worse by triggering shivering.
• Check on them through the night, particularly children, babies and older adults.
• Keep children off school or nursery while they have a fever and are feeling unwell.

Trusting your instincts

Guidelines are useful, but they cannot cover every situation. If you are worried about someone with a high temperature — particularly a baby, a young child or an older adult — contact your GP surgery, call 111, or seek urgent care. You know the person you are caring for better than anyone, and a clinician would far rather see you and be able to reassure you than have you wait at home and worry.