General
Fever
A fever is a rise in body temperature, usually above 38°C, and is most often a sign that the body is fighting an infection.
Education and reference only. This explains the common causes of fever and the warning signs that need urgent help, in plain language — it is not a diagnosis or a substitute for advice from a clinician. If you feel very unwell or are worried, seek medical help.
Quick answer
What is fever?
A fever means your body temperature is higher than normal, typically taken to be 38°C or above. It is a natural response that usually shows your immune system is responding to an infection, most commonly a viral or bacterial illness.
- Get urgent help: A rash that does not fade when you press a glass against it, in someone who is unwell, can signal meningococcal infection — call 999. Signs of sepsis such as confusion or disorientation, very fast or laboured breathing, mottled or blotchy skin, or not having passed urine all day — call 999.
- Self-care: For a mild fever in an otherwise well adult or child, rest and drink plenty of fluids to avoid becoming dehydrated.
About fever
A fever means your body temperature is higher than normal, typically taken to be 38°C or above. It is a natural response that usually shows your immune system is responding to an infection, most commonly a viral or bacterial illness. A fever is a symptom rather than an illness in itself, so the most useful thing is to work out what is causing it and how unwell the person is overall. Most fevers in otherwise healthy adults settle on their own within a few days. What matters more than the exact number on the thermometer is how the person looks and behaves: someone who is alert, drinking and able to be comforted is usually less of a concern than someone who is drowsy, confused or struggling to breathe. Fever in very young babies, in people with weakened immune systems, and fever accompanied by certain warning signs needs prompt assessment.
When to get help
Call 999 or go to A&E if fever comes with any of these warning signs:
- A rash that does not fade when you press a glass against it, in someone who is unwell, can signal meningococcal infection — call 999.
- Signs of sepsis such as confusion or disorientation, very fast or laboured breathing, mottled or blotchy skin, or not having passed urine all day — call 999.
- A very high temperature in a baby under 3 months, or a fever in any young baby who seems unwell, floppy or hard to wake — seek emergency care.
- A stiff neck, dislike of bright light, or a severe headache with the fever can point to meningitis — get urgent help.
- A fit or seizure, a fever that will not come down at all, or a person who is becoming increasingly drowsy or hard to rouse — call 999.
When to see a doctor
Contact a doctor if a fever lasts more than three days or keeps coming back, if you feel increasingly unwell rather than gradually better, or if you have a long-term condition or weakened immune system that makes infections more risky. Seek advice for a fever with a persistent cough, pain passing urine, a spreading rash, or pain that is getting worse. Anyone who has recently travelled abroad and develops a fever should mention this, as some infections need specific tests. Trust your instincts: if you are worried about yourself or your child, it is always reasonable to ask for medical advice.
Not sure how urgent it is? It is always OK to call NHS 111 for advice, day or night.
What can cause it
Common causes of fever
Fever has many possible causes. Each links to a full, plain-language guide to that condition — what it is, how it's treated and when to seek help.
What helps
Self-care and what you can do
For a mild fever in an otherwise well adult or child, rest and drink plenty of fluids to avoid becoming dehydrated. Wear light clothing and keep the room at a comfortable temperature rather than wrapping up too warmly. There is no need to force a fever down with cold sponging, which can make a person shiver and feel worse. Keep an eye on how the person is behaving rather than fixating on the thermometer reading, and check on them regularly, including overnight if they are a child. Offer small, frequent drinks if they do not feel like eating much. Most simple fevers ease over a few days as the underlying infection settles.
Answers
Fever: frequently asked questions
What temperature counts as a fever?
A fever is generally taken to be a temperature of 38°C or above. However, how unwell the person seems matters more than the exact figure, so always consider their overall behaviour as well as the reading.
Should I try to bring a fever down?
A mild fever does not always need treating, as it is part of how the body fights infection. Focus on keeping the person comfortable, well hydrated and rested, and watch for warning signs rather than trying to force the temperature down with cold sponging.
When is a fever in a child an emergency?
Seek emergency help if a child has a non-fading rash, a stiff neck or dislike of light, is unusually drowsy or floppy, is breathing very fast, or is a baby under three months with any fever. If you are seriously worried, call 999.
How long should a fever last?
Most simple fevers from common infections settle within three to four days. If a fever lasts longer, keeps returning, or you feel increasingly unwell, contact a doctor for advice.
Sources
Where this is drawn from
- NICE CKS: Feverish children — risk assessment.
- Meningitis Research Foundation
Related symptoms
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