Fever

Overview

A fever is when your body temperature is higher than normal. Most doctors count a temperature of 38°C (100.4°F) or above as a fever. Fever is not an illness on its own — it is a sign. It usually means your body is fighting an infection, such as a cold, flu, or a stomach bug. In fact, a raised temperature is part of how your immune system (your body's defence system) works. It helps make the body a less comfortable place for germs. Most fevers are harmless and settle within a few days, but they can sometimes be a sign of something that needs medical attention.

Yes, fever is extremely common. Almost everyone gets a fever at some point, and young children often have several each year as their immune systems learn to fight off infections.

Fever can affect anyone at any age. It is most common in babies and young children, because they catch lots of infections and their immune systems are still developing. Older adults and people with weakened immune systems can also be affected, and for them a fever may need to be checked sooner.

Symptoms

Common symptoms

• Skin that feels hot to the touch
• Feeling shivery or having chills, even when warm
• Sweating or feeling clammy
• Headache
• Aching muscles and feeling generally unwell
• Tiredness and low energy
• Lack of appetite
• Feeling thirsty or having a dry mouth
• Flushed or red cheeks

Symptoms in children

• Being more irritable or clingy than usual
• Crying more, or crying in a way that is hard to soothe
• Being sleepier than usual, or floppy and hard to wake
• Not wanting to feed or drink, or fewer wet nappies than usual
• Fast breathing
• Shivering or having a fit (convulsion) — this can happen with a sudden high temperature in young children
• Complaining of a sore throat, earache, or tummy ache

Symptoms in older adults

• A temperature that is only slightly raised, or even normal — older bodies sometimes do not mount a big fever
• New confusion, drowsiness, or being 'not themselves'
• Weakness, unsteadiness, or a fall
• Feeling cold and shivery rather than hot
• Not drinking enough, leading to dehydration
• Less appetite and reduced interest in usual activities

Causes

Main causes

• Viral infections such as colds, flu, and childhood viruses — these are the most common cause
• Bacterial infections such as throat infections, ear infections, urine infections, or pneumonia
• Stomach bugs that cause vomiting or diarrhoea
• Some infections passed by insects, such as malaria, especially after travel
• Reactions to some medicines or vaccinations (usually mild and short-lived)
• Heat-related illness, such as heat exhaustion
• Inflammatory conditions, where the body's own immune system causes heat and swelling
• In rare cases, serious conditions such as a severe infection of the blood or tissues

Risk factors

• Being a baby or young child
• Being an older adult, especially over 65
• Having a weakened immune system, from illness or certain treatments
• Being in close contact with people who are unwell, such as in a nursery, school, or care home
• Recent travel to areas where infections like malaria are common
• Not being up to date with routine vaccinations
• Long-term conditions such as diabetes or lung disease

When to see a doctor

See a doctor urgently if:

• A baby under 3 months with any temperature of 38°C or above
• A child who is floppy, very drowsy, or hard to wake
• A rash that does not fade when pressed
• Breathing that is fast, noisy, or difficult
• A fit or convulsion
• Signs of dehydration, such as no urine for many hours or a dry mouth
• Fever with a severe headache, stiff neck, or dislike of light
• Fever in someone with a weakened immune system

Book a routine appointment if:

• A fever that keeps coming back over several weeks
• A fever with weight loss, night sweats, or ongoing tiredness
• Repeated fevers in a child, even if they seem well in between
• A fever with a sore throat, earache, or cough that is not improving after a few days
• You feel worried or unsure — it is always reasonable to ask for advice

Diagnosis

A doctor or nurse will usually start by asking about the symptoms, how long the fever has lasted, and any recent travel or contact with people who are ill. They will check the temperature and examine the person, looking at the throat, ears, chest, and skin, and checking for a rash. Most fevers are diagnosed from this alone.

Tests that may be done

• A urine test to check for a urine infection, especially in young children
• A throat swab or nose swab to look for particular infections
• A blood test to check for infection or inflammation
• A chest X-ray if a lung infection is suspected
• Tests for specific infections if there has been recent travel

What to expect at your appointment

In most cases, the cause of a fever is never pinned down exactly, because it settles quickly and tests are not needed. If tests are done, results may take a few hours or days. You will usually be given advice on how to keep the person comfortable and told what warning signs to look out for.

Treatment

The main aim is to make the person comfortable and to watch for any signs of something more serious. Fever itself rarely needs treating, but if someone is distressed or uncomfortable, medicines to lower temperature and ease aches are available. Your pharmacist can advise on what is suitable for the person's age and situation. Always read the label and follow the instructions, and never give medicine to a child without checking it is right for their age.

Self-care at home

• Rest as much as you need to
• Drink plenty of fluids — water is best, and small sips often are easier than large amounts at once
• Wear light clothing and use a light sheet rather than heavy blankets
• Keep the room at a comfortable, cool temperature and let fresh air in
• Check the temperature regularly, but not so often that it becomes a worry
• Do not sponge with cold water or use ice baths — these can make things worse
• For children, keep offering drinks and check their nappies or how often they pass urine
• Ask your pharmacist if you are unsure about any medicine, including for children and babies

Medical treatments

Treatment depends on the cause. If the doctor finds a bacterial infection, they may prescribe antibiotics — these do not work on viruses like colds and flu. For viral infections, the body usually clears the infection itself with time and supportive care. If someone is very unwell, has a serious infection, or cannot keep fluids down, they may need fluids or treatment in hospital. A doctor will always weigh up what is needed for the individual person.

When is surgery considered?

Surgery is not relevant for fever itself, though in rare cases a fever may be caused by a condition that needs a procedure — your doctor would explain this if it applied.

Living with this condition

When someone has a fever, the priority is comfort, fluids, and rest. Keep checking how they seem in themselves rather than focusing only on the thermometer number. It helps to write down the times and temperatures, what they have had to drink, and any other symptoms, so you can give clear information if you speak to a doctor. Children can usually go back to nursery or school once their fever has settled and they feel well enough.

Lifestyle tips

• Keep up good handwashing at home to reduce spreading infections
• Keep the home well ventilated and avoid overheating rooms
• Make sure everyone gets enough sleep and rest
• Stay away from others when unwell, especially people who are vulnerable
• Keep a simple thermometer at home and learn how to use it correctly
• Keep a note of the local health advice number or your doctor's out-of-hours service

Diet and exercise

There is no special diet for fever. Offer fluids often — water, diluted juice, or milk for children — and do not worry if appetite is low for a day or two, as long as the person is drinking. When they feel ready, gentle foods are fine. Avoid intense exercise while the fever is present; light activity such as walking around the house is fine once energy returns. Wait until the fever has been gone for a day or so before returning to normal exercise or sport.

Mental health and emotional wellbeing

Fevers can be worrying, especially for parents of young children, and it is normal to feel anxious when a temperature is high or keeps coming back. Not getting enough sleep while caring for someone unwell can also wear you down. Talk to someone you trust, ask for practical help, and contact your doctor or pharmacist with any questions — no concern is too small. If worry or low mood is becoming hard to cope with, please reach out for support: speak to your doctor, or contact your local crisis or mental health support service. If you or someone else is in immediate danger, call your local emergency number.

Prevention

You cannot prevent every fever, since infections are part of everyday life and a fever is a normal immune response. But you can lower the chances of catching and spreading infections that cause fever, and reduce the risk of heat-related fevers.

Vaccines

Staying up to date with routine vaccinations, including those offered in childhood and any recommended for adults, helps protect against many infections that cause fever. Vaccines given in pregnancy also help protect newborn babies. Ask your doctor or health clinic what is recommended for you and your family.

Screening programmes

There is no screening test for fever itself. However, regular health checks for babies and young children, and for people with long-term conditions, help pick up problems early.

Complications

If left untreated

• Dehydration, especially in babies and older adults who may not drink enough
• Febrile convulsions (fits) in some young children, which are usually brief and not harmful
• The underlying infection going unrecognised and becoming more serious
• Heat exhaustion or heatstroke if the fever is caused by overheating
• Rarely, serious infections that need urgent hospital care

Long-term outlook

The great majority of fevers settle within a few days with no lasting effects. Fever is a normal, helpful sign that the body is responding to infection, and most people recover fully. Knowing the warning signs means you can act quickly if something more serious is going on — and that early action is exactly what keeps outcomes good.

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