Normal body temperature is different for everyone. It changes as you get older and also during the day, but is usually between 36 and 36.8 degrees Celsius.
A high temperature or fever is when your body temperature is 38 degrees Celsius or higher. It can be a sign that you are unwell. It usually means you have an infection, such as a cold. But it can also be a sign of something more serious. For example, a cold, flu or COVID-19 (coronavirus).
A fever is usually caused by your body fighting a viral or bacterial infection. It usually lasts around 3 to 5 days. Most people recover from a mild fever with self-care at home.
This page has general information about fever in adults. If you have a child with a fever, see the information on fever in children.
Symptoms
Your symptoms will depend on the type of fever you have.
Mild fever (38 to 38.9 degrees Celsius)
With a mild fever, you might:
- have flushed cheeks
- feel tired
- be warm to the touch
You will usually be able to carry out normal daily activities.
High fever (39 to 39.9 degrees Celsius)
With a high fever, you might:
- feel hot to the touch
- not feel well enough to go to work
- have aches and pains
Very high fever (40 degrees Celsius or higher)
With a very high fever, you:
- might want to stay in bed or be inactive
- do not feel well enough to carry out normal activities
- feel hot to the touch
- may have lost your appetite
When to see a GP
Most people, including children and infants older than 3 months, do not need medical treatment for a mild fever.
You should contact your GP if you:
- have a very high fever (40 degrees Celsius or higher)
- are still feverish after 3 days or your symptoms get worse
- are shivering, cannot stop shaking, or have chattering teeth, and it does not stop within an hour or so
- have a severe headache that does not get better after taking painkillers
- have trouble breathing
- are confused or drowsy
- have travelled overseas recently
Urgent advice: Contact your GP immediately if
you have a fever and notice the following symptoms:
- severe headache
- stiff neck
- sensitivity to light
These symptoms may be a sign of meningitis. This needs urgent medical attention.
Pregnant women
If you are pregnant and have a temperature of 38.5 degrees Celsius, or any fever lasting for 3 days or more, see your GP. They need to monitor the effects of the fever on your baby.
Causes of fever
Fever is usually caused by a viral or bacterial infection. Fever is your body's way of fighting infection. Raising your body temperature helps to kill the virus or bacteria.
Common conditions that can cause fevers include:
- respiratory tract infections
- flu (influenza) and flu-like conditions
- colds
- tummy bugs (gastroenteritis)
- ear infections
- infection of your tonsils (tonsillitis)
- kidney or urinary tract infections
You might also have a mild fever after getting a vaccine.
Treatment
Medicine is not needed for a mild fever. You can use paracetamol if you also have a headache, pain or distress.
Managing a fever yourself
Drink plenty of fluids, especially water (little and often is best). Try to drink 2 to 3 litres in 24 hours while you have a fever. This will reduce the risk of dehydration.
Do
-
get plenty of rest
-
make sure the room temperature is comfortable - not too hot or too cold
-
open a window for ventilation if you can, but avoid draughts
-
wear lightweight clothing and use lighter bedding
-
use a cool cloth to wash your face, hands and neck
-
change bed linen and clothing regularly
Don't
-
do not use hot water bottles or electric blankets
Content supplied by the NHS and adapted for Ireland by the HSE
