Your child’s average body temperature is about 37°C. If your child’s temperature is higher than 38°C for 24 hours or more, she probably has a fever. A fever is a sign of illness.
Causes of fever and high temperature in children
Fever is not an illness in itself, but is the sign of an illness.
Children get fevers for all kinds of reasons. Most fevers and the illnesses that cause them last only a few days. But sometimes a fever will last much longer, and might be the sign of an underlying chronic or long-term illness or disease.
Infections are by far the most common cause of fever in children. In general, fever is nature’s response to infection, and can actually help the body fight infection.
Most of these infections are caused by viruses, which are responsible for colds and upper respiratory infections, as well as the common infectious diseases of childhood, such as chickenpox. These infections don’t last long and usually don’t need to be treated.
Some infections are caused by bacteria, and need treatment with antibiotics. These include certain ear and throat infections, urinary tract infections, pneumonia, blood infections and meningitis. A very sore throat with a fever can be caused by streptococcus. If it isn’t treated with antibiotics, this infection can lead to rheumatic fever or heart damage.
There are other less common causes of fever. These include allergic reactions to drugs or vaccines, chronic joint inflammation, some tumours and gastrointestinal diseases, like gastroenteritis.
During the course of each day, body temperature goes up and down by up to one degree. It’s usually lowest in the early hours of the morning, and highest in the late afternoon and early evening.
A fever or high temperature might come on slowly and rise over a few days, or it might rise very quickly. The height of a fever, and how quickly it comes on, usually doesn’t have anything to do with the illness that causes it.
Fever in itself is rarely harmful. But the high temperature might make your child feel uncomfortable – he might have chills or shivering when his temperature is rising, and might sweat when it’s falling. Sometimes he might become mildly dehydrated if he’s losing a lot of fluid from the fever and not replacing it.
Febrile convulsions are seizures that happen because of fever. They occur in about 4% of children between the ages of six months and five years. Children outgrow febrile convulsions by the age of 4-5 years. Febrile convulsions have no long-term consequences, but you should talk to your doctor about them.
Sometimes your child might appear flushed, and her skin might feel warm, but her core (inner body) temperature will be quite normal. This can happen when your child has a cold or has done some hard physical activity. It can also happen on a very hot day.
When to see your doctor about fever and high temperature
Babies under three months of age who develop a fever must be seen by a doctor immediately, because it’s harder to tell if they have a serious underlying illness.
In children under 12 months, fever might be a sign of a more significant illness, and you do need to seek medical advice.
In children over 12 months, seek medical attention if your child:
- looks sicker than before – more pale, lethargic and weak
- has trouble breathing
- becomes drowsy
- refuses to drink, and is weeing less often (if your baby has fewer than half the usual number of wet nappies, see a doctor)
- complains of a stiff neck, persistent headache or light hurting his eyes
- vomits persistently, or has frequent bouts of diarrhoea
- doesn’t improve in 48 hours
- suffers pain
- has a fever above 40°C
- is causing you to worry for any other reason.
A fever will run its course regardless of treatment. Fever is a result of the body’s attempt to fight an infection. Your child’s temperature will return to normal when the infection or other cause of the fever has completely gone.
In older children, treat the fever only if you feel it’s making your child uncomfortable, irritable or so lethargic that she can’t drink enough fluids.
Generally, children handle fever well, but you can do a few things to make your child more comfortable:
- Dress your child in light clothing.
- Give your child frequent small amounts of clear fluids, like water, to drink. If your child isn’t hungry, that’s OK. The most important thing is to make sure he’s drinking enough to avoid dehydration. If your child is under six months old you should breastfeed often and/or give cooled boiled water.
- Give your child liquid paracetamol in the correct and recommended dose. Giving your child more than the recommended dose can cause liver damage. It’s important not to give fever-lowering medication too often or for prolonged periods, because it can cause side effects.
Cool baths, sponging and fans can actually make your child more uncomfortable.
You must not give your child aspirin for any reason.
Aspirin can make your child susceptible to Reye’s syndrome
, a rare but potentially fatal illness. It can also cause serious illness or even death in children with chickenpox or flu symptoms.
Taking your child’s temperature
You might want to take your child’s temperature if your child is:
- unwell and feels warmer than usual
- irritable and crying
- more sleepy than usual
- in pain
- refusing to drink, or vomiting.
Using a thermometer is the best way to check your child’s temperature. Feeling your child’s skin temperature (for example, by putting your hand to her forehead) isn’t always a reliable way of diagnosing a fever.
There are several different methods for taking a child’s temperature using a thermometer:
- orally – putting a digital thermometer in your child’s mouth under the tongue
- rectally – putting the thermometer a little way into your baby’s rectum
- axillary – putting the thermometer under your child’s armpit
- aurally – putting a digital ear thermometer into your child’s ear, which can be a little inaccurate
- superficially – wiping a device called a temporal artery thermometer across your child’s forehead.
Your GP or child and family health nurse nurse can also show you how to take your child’s temperature with a thermometer.
It’s hard to take an oral temperature if your child is under five years because he might not cooperate. If your child has a blocked nose because of a cold, he might find it hard to breathe with his mouth closed.
To take an oral temperature:
- Wait five minutes after your child has had a hot or cold drink (or it will affect the temperature).
- Place the thermometer well under one side of your child’s tongue.
- Have your child hold it in place with her lips, not her teeth, and tell her to breathe through her nose.
- Wait until the thermometer beeps before taking a reading.
Oral readings can be around half a degree lower than body temperature.
Rectal thermometers are best used for babies and young children under 12 months (older children will probably protest loudly!). Rectal readings are most reliable for babies under three months.
Taking a rectal temperature is often difficult, especially when your baby is very active – the thermometer can slide out of the rectum, or the tip of the thermometer might damage the lining of the rectum.
Place the tip of a digital thermometer just inside your child’s anus and wait for it to beep before taking a reading.
Taking your child’s temperature under the armpit is usually the safest method, especially in young children. Unfortunately, it’s also the least accurate method.
Place the thermometer in your child’s armpit and close his arm, holding his elbow against his body. Wait for the thermometer to beep before taking a reading.
Armpit readings can record a temperature up to 1 degree lower than the actual body temperature.
Mercury thermometers can poison a child if they break. If you’re using a mercury thermometer, consider replacing it with one of the thermometers below.
Ear thermometers (infrared tympanic thermometers)
These are quick and easy to use. Your doctor or nurse can show you how to place the thermometer in your child’s ear canal, so you get a reasonably accurate reading.
You put a plastic cover over the tip of the thermometer and put the tip gently just inside your child’s ear canal, until the thermometer beeps.
It’s accurate to within about a degree, as long as the ear canal doesn’t have too much wax in it.
Temporal artery thermometers
These are the simplest thermometers to use. The thermometer is scanned across your child’s forehead. An advantage of these thermometers is that you can check a sleeping child without waking her.
These are good if your child already uses a pacifier. Infants or toddlers who don’t use pacifiers will usually resist a pacifier thermometer, so something else might be easier to use.
One type of thermometer involves a plastic strip that you put on your child's forehead to get a digital reading of your child’s temperature. This system isn’t very accurate – at best, it can give you only a rough guide to your child’s temperature.