Fever (high temperature): symptoms, how long it lasts and when to get help

The NHS says normal body temperature is different for everyone and changes during the day. A high temperature is usually considered to be 38C or above, and this is sometimes called a fever.

Tommy's describes a high temperature as a symptom of an underlying issue rather than an illness in itself.

The NHS says you may have a high temperature if:

• Your chest or back feels hotter than usual.

• You feel hot or cold, feel shivery (chills), sweat, or your skin is warm and red (this may be harder to see on black or brown skin).

• A thermometer says your temperature is 38C or above.

• Tommy's adds a headache, fatigue and muscle aches as common signs.

The NHS says you do not need a thermometer to know you have a high temperature, but you can use one. For adults it suggests a digital thermometer under the tongue or in the armpit, or a digital ear thermometer following its instructions.

It says not to use a glass thermometer because they can be dangerous, an infrared thermometer because some do not meet UK regulations, or forehead strips because they are not accurate.

For children the NHS suggests placing a digital thermometer inside the top of the armpit. NICE says forehead chemical thermometers are unreliable.

The NHS suggests:

• Get lots of rest.

• Drink plenty of fluids (water is best) to avoid dehydration; drink enough so your pee is light yellow and clear.

• Take paracetamol or ibuprofen if you feel uncomfortable.

• Try to stay at home and avoid contact with other people until you do not have a high temperature.

For children, the NHS says the temperature should go down over 1 to 4 days, and to call NHS 111 if a child has a high temperature that has lasted 5 days or more.

For adults, the NHS page does not give a number of days. It says to ask for an urgent GP appointment or get help from NHS 111 if a high temperature you have been treating at home is not getting better or is getting worse.

The NHS also notes that sometimes a high temperature could be a sign of something more serious if it is very high or will not come down.

The NHS says a high temperature is very common in young children. You can usually look after them at home: give plenty of fluids (continue breastfeeding), keep them at home, check on them regularly including at night, and give paracetamol or ibuprofen if they are distressed or uncomfortable.

The NHS says not to undress your child or sponge them down to cool them, not to cover them in too many clothes, not to give aspirin to children under 16, and not to alternate ibuprofen and paracetamol unless a health professional tells you to. It says not to give paracetamol to a child under 2 months, and not to give ibuprofen to a child under 3 months or weighing under 5kg.

Tommy's says a high temperature is 38C or above, but even 37.5C could be a sign of a hidden infection. It says to call your GP, midwife or hospital maternity unit if your temperature is above 37.5C, even if you have no other symptoms, because some infections can make you really unwell or harm your unborn baby.

It says paracetamol is safe in pregnancy at the dose listed on the packet, and to drink plenty of water. It advises not taking decongestants or NSAIDs such as ibuprofen while pregnant.

Tommy's lists possible causes including a cold, flu, COVID-19 or a urinary tract infection, and in rare cases something more serious such as sepsis.

The NHS says many things can cause a high temperature and it is not usually a sign of anything serious. It is often just caused by your body fighting an infection, such as a cold or flu.

In children, the NHS says it is the body's natural response to infections like coughs and colds. It lists common childhood illnesses like chickenpox and tonsillitis, and vaccinations.

The NHS says sepsis is a serious reaction to an infection that can be life-threatening and develops very quickly. In adults and children aged 5 or over, it says to call 999 or go to A&E if there is:

• Very fast breathing.

• Confusion, slurred speech or not making sense.

• Blue, pale or blotchy skin, lips or tongue.

• A very high or very low temperature, feeling hot or cold to the touch, or shivering.

• A rash that does not fade when you press it.

• Any symptom you are worried might be sepsis.

For most fevers, self-care at home and pharmacy advice are enough. NHS 111 is the route for urgent but non-emergency advice. If a fever has no clear cause or keeps returning, a GP can arrange tests; private GP and urgent care services are also available, and their findings are best shared with your own GP.