Fever in adults

This page provides general information about fever. If you have a child with a fever, see fever in children.

Prevent the spread of COVID-19

A fever (high temperature - 38 degrees Celsius or above) can be a symptom of COVID-19.

Get advice about symptoms of COVID-19 and what to do

Your body’s normal temperature is between 36 and 36.8 degrees Celsius.

A high temperature or fever, for most people, is when your body temperature is 38 degrees Celsius or higher. This can be a sign that you are unwell. It usually means you have an infection such as a cold. But it can also be due to more serious infections, such as COVID-19 (coronavirus).

Read about the symptoms of COVID-19

Even if you don’t have a high temperature you may still be seriously ill. So it's important to look at all your symptoms.

A fever is usually caused by your body fighting a viral or bacterial infection.

A fever usually lasts 3 to 5 days and most people will recover from a mild fever with self-care at home.


Mild fever (38 to 38.9 degrees Celsius)

With a mild fever you might have flushed cheeks, feel tired and be warm to touch. You will generally be able to carry out normal daily activities.

High fever (39 to 39.9 degrees Celsius)

With a high fever, you’ll feel hot to touch. You may not feel well enough to go to work and you may have aches and pains.

Very high fever (40 degrees Celsius or higher)

With a very high fever, you will usually want to stay in bed or be inactive – you won’t feel well enough to carry out normal activities. You’ll feel hot to touch and you may have lost your appetite.

When to see a GP

Young babies and pregnant women

Babies under 3 months old with fever must be checked by your GP. Contact your GP if your baby is between 3 and 6 months and has a high or very high fever. Read more about fever in children.

If you’re 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.

Other ages

Older infants, children and adults will not usually need any medical treatment for mild fever, especially if you are otherwise well.

You should contact your doctor if you:

  • have a very high fever (over 40 degrees Celsius)
  • are still feverish after 3 days of home treatment or seem to be getting sicker
  • are shivering or shaking uncontrollably, or have chattering teeth, and it doesn’t stop within an hour or so
  • have a severe headache that doesn’t get better after taking painkillers
  • are having trouble breathing
  • are getting confused or are unusually drowsy
  • have recently travelled overseas

Urgent advice: Contact your GP immediately if

you notice the following symptoms (along with a fever):

  • severe headache
  • stiff neck
  • sensitivity to light

These symptoms may be a sign of meningitis. This needs urgent medical attention.

Causes of fever

Fever is usually caused by a viral or bacterial infection. Fever is your body's way of fighting infection. Raising the temperature inside your body helps to kill the virus or bacteria causing the infection.

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
  • common childhood illnesses, such as chickenpox, scarlet fever, rubella (German-measles), whooping cough and rheumatic fever

You might have a mild fever after getting a vaccine.

Adults should not take paracetamol before or after getting a vaccine. It may make the vaccine less effective.


Medication for fever

Fever is your body’s way of fighting infection. Medication is not needed for mild fever, but you can use paracetamol if you also have a headache, pain or distress.

Self management

  • Drink plenty of fluids, especially water (little and often is best). Aim for 2 to 3 litres in 24 hours while you have a fever. This will reduce the risks of dehydration.
  • Get plenty of rest. Sleeping for 2 to 3 hours at a time is slightly better than just resting.
  • Make sure the room temperature is comfortable - not too hot or too cold.
  • If possible, open a window for ventilation but avoid draughts.
  • Wear lightweight clothing and use lighter bedding.
  • Do not use hot water bottles or electric blankets.
  • Use a cool cloth to wash face, hands and neck.
  • Change bed linen and clothing regularly.

Content supplied by the NHS and adapted for Ireland by the HSE

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This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

Page last reviewed: 18 March 2020
Next review due: 18 March 2023