Fever is when your core body temperature is raised above 37.5 degrees Celsius.
If you have any respiratory symptoms such as a cough, sore throat, shortness of breath, head cold or loss of smell, with or without fever, call your GP or Healthline's dedicated COVID-19 number 0800 358 5453 to check whether you need to be tested for COVID-19.
This page provides general information about fever. If you have a child with a fever, see fever in children.
Key points about fever
- A fever is usually caused by your body fighting an infection.
- On its own, a fever doesn't mean you are seriously sick, but you need to check for other signs of illness.
- A fever usually lasts 3–5 days and most people recover from a mild fever with self-care at home.
- However, there are times when you should see a doctor urgently for fever.
What is a fever?
Fever is when your core body temperature is higher than 37.5 degrees Celsius. Usually, you will feel unwell and hot, and you may sweat. Sometimes you will feel very cold and shiver even when your temperature is high.
Mild fever: You have a mild fever if your temperature is higher than 38ºC.
High fever: A high fever usually means more than 39ºC.
Use a thermometer to find out how high your temperature is. Read more about thermometers and how to use them.
When should I seek help for my fever?
Most fevers aren't life-threatening, but sometimes you need to seek medical advice.
When should I see a doctor urgently?
See your doctor or go to an emergency department immediately if you notice the following symptoms with a fever:
These symptoms may indicate meningitis, which needs urgent medical attention.
Phone Healthline on 0800 611 116 if you are worried and not sure what to do. If you have already seen a doctor but your symptoms get worse, go back for another check.
When should I see a doctor?
You should see your doctor if you have a fever and have the following underlying conditions:
You should also see your doctor if you:
What causes fever?
A viral infection is the most common cause of a fever. A bacterial infection is less common but is more serious. Your body's natural reaction to infection is to raise your body temperature. This helps kill the infection. Vaccination sometimes causes a mild fever too.
Do I need medicine for fever?
Fever is your body’s way of fighting infection. Medicine is not needed for mild fever, but you can use paracetamol if you also have a headache or muscle pain.
How do I care for myself with fever?
- Drink plenty of fluids, especially water or rehydration fluid (little and often is best). Aim for 2–3 litres in 24 hours while you have a fever.
- Get plenty of rest.
- 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 your face, hands and neck.
- Change bed linen and clothing regularly, especially if they are wet from sweat.
- Fever in adults Ministry of Health, NZ, 2017
- Fever and night sweats Patient Info, UK, 2015
- Cold season – managing without antibiotics BPAC, NZ, 2018
- Danger signs during pregnancy Ministry of Health, NZ, 2017
- Fever in adults NHS Inform, UK, 2020
|Dr Sharon Leitch is a general practitioner and clinical research training fellow in the Department of General Practice and Rural Health at the University of Otago. Her area of research is patient safety in primary care and safe medicine use.|