Your normal body temperature is approximately 37C (98.6F).
A fever is usually when your body temperature is 38C (100.4F) or more. You may feel warm, cold or shivery.
You can find out if you have a fever by using a thermometer to take your temperature.
What causes a fever?
A fever is your body's natural response to many common illnesses such as:
Fever helps your body fight infections by stimulating your immune system: your body’s natural defence. By increasing your body’s temperature, a fever makes it harder for the bacteria and viruses that cause infections to survive.
When to get help
If any of the following applies, please contact your GP practice:
- you have severe thirst or reduced urine output
- you are passing urine that is darker than normal
- you are light-headed or weak
- you have new, severe muscle cramps
- your symptoms have worsened or you notice new symptoms
- you've had a fever after recent foreign travel
If your GP practice isn't open, phone NHS 24's 111 service.
Fever and underlying health issues
Most fevers aren't in themselves life-threatening, however there are certain times where you may need to seek medical advice.
If any of the following apply to you and you have a fever, please contact your GP practice immediately:
- You are on treatment for immune deficiency
- You are on immune-suppressant drugs, such as regular steroids, methotrexate, azathioprine or cyclophosphamide
- You are taking medication where you have been warned about a risk of a reduced immune system
- You are on, or recently completed, treatment for cancer, leukaemia or lymphoma
- You are a transplant recipient
- You are HIV positive
Fever and your medical history
If you have a fever and any of the following medical conditions you should contact your GP practice immediately.
- Chronic lung disease
- Asthma which has been treated with medication in the last 3 years
- Heart disease (excluding blood pressure which is currently well controlled)
- Diabetes or another metabolic disease
- Chronic gastrointestinal or liver disease
- Chronic renal (kidney) disease
- Cystic fibrosis
- Neurological conditions such as cerebral palsy, stroke, multiple sclerosis or muscular dystrophy
- Sickle cell disease
Treating a fever
Most fevers will improve of their own accord in a few days. However, there are a number of things you can do to help the uncomfortable feelings associated with a fever.
- Don't over dress. Wear loose comfortable clothing and make sure the room you are in isn't too warm. You shouldn't attempt to make yourself feel cold.
- Drink more fluids, avoiding alcohol as this can make dehydration worse. You sweat more when you have a fever and drinking makes sure you wont get dehydrated. You should be passing urine approximately every 6 hours. A pale yellow urine means you're unlikely to be dehydrated.
- Take a medicine that reduces fever such as paracetamol (unless you're allergic or have been told by a healthcare professional that you can't take it).
Fever in children
Fever affects people of all ages, however it often affects babies and younger children in response to minor illnesses such as:
Find out more about fever in children.