Fever in Adults: What It Means and When to See a Doctor

A fever can make you feel hot, shivery and miserable, and it often worries people. In most adults it is the body's response to an everyday infection. This article explains what a fever is, how to check it properly, what you can do at home, and when it is time to speak to a doctor.

What is a fever?

According to the NHS, a high temperature (fever) in adults is usually a reading of 38°C or above. Normal body temperature is not exactly the same for everyone, and it changes a little during the day. A fever is not an illness by itself. It is a sign that something is going on in the body, most often an infection.

How to tell if you have a fever

You may notice some of these signs:

• Your chest or back feels hotter than usual to touch
• You feel shivery, or you are sweating
• Your skin looks warm and red (this can be harder to see on brown or black skin)

The NHS also points out that you can feel hot or cold even when a thermometer reads below 38°C, and you may still have a high temperature. A digital thermometer placed under the tongue or in the armpit is suitable. The NHS advises against glass thermometers, infrared thermometers and forehead strips, because they are less reliable or less safe.

Common reasons for a fever

Many everyday infections can raise your temperature. Colds, flu and COVID-19 are well known examples. Fever can also be an early sign of mosquito-borne illnesses such as dengue, chikungunya and malaria, and of infections such as typhoid. These illnesses can look alike at the start, which is why a doctor may suggest tests rather than guessing. Other causes also exist, so a fever that is unexplained or does not settle should be checked.

Looking after yourself at home

For a simple fever, the NHS suggests these steps:

• Rest as much as you can
• Drink plenty of fluids, with water a good choice
• Stay at home and avoid close contact with other people until your temperature has returned to normal
• If you feel uncomfortable, ask a pharmacist or doctor which common over-the-counter fever and pain reliever is safe for you

Always read the label and ask a professional if you are unsure, especially if you have a long-term condition, are pregnant or take other medicines. If you suspect dengue, do not reach for painkillers without advice. The WHO notes that some common painkillers, including ibuprofen and aspirin, can raise the risk of bleeding in dengue.

Antibiotics do not work on viruses. According to the CDC, colds, flu and most sore throats and chest colds are caused by viruses, so antibiotics will not help them. A doctor decides whether an antibiotic is needed for your situation.

When to see a doctor

The NHS advises asking for an urgent appointment, or contacting a health helpline, if your high temperature is not getting better after looking after yourself at home, or if it is getting worse. NHS guidance on colds also lists these reasons to see a doctor:

• A fever that lasts more than 3 days
• A very high temperature, or feeling hot, cold and shivery at the same time
• Shortness of breath or chest pain
• Symptoms that are getting worse or have not improved after 10 days
• A long-term health condition, such as diabetes, or a weakened immune system

In the NHS COVID-19 guidance, a high temperature lasting 5 days or more is also a reason to seek urgent advice. People who are pregnant, aged 60 or over, or have a weakened immune system should seek help promptly.

Fever can sometimes be a sign of sepsis, a serious reaction to infection. The NHS lists confusion or slurred speech, uncontrollable shivering, muscle pain, difficulty breathing, blue, grey or blotchy skin, and passing very little or no urine as warning signs in adults. The NHS says to call emergency services or go to hospital immediately if you think someone might have sepsis, and not to drive yourself.

In an emergency, call your local emergency number (112 in India, 911 in the United States).

Quick summary

A fever is a signal, not a diagnosis. Rest, fluids and staying away from others are the basics. If the fever is high, lasts more than a few days, keeps rising, or comes with breathing trouble, confusion or any other worrying sign, speak to a doctor. This article is for education and cannot replace advice from a doctor who can examine you.