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A fever also known as a high fever or a high temperature is not by itself an illness. It’s usually a symptom of an underlying condition, most often an infection.
Fever is usually associated with physical discomfort, and most people feel better when a fever is treated. But depending on your age, physical condition, and the underlying cause of your fever, you may or may not require medical treatment for the fever alone. Many experts believe that fever is a natural bodily defense against infection. There are also many non-infectious causes of fever.
Fever is generally not considered dangerous, but hyperthermia can cause dangerous rises in body temperature. This can be due to an extreme temperature associated with heat injury such as heat stroke, side effects of certain medications or illicit drugs, and stroke. With hyperthermia, the body is no longer able to control body temperature.
Causes of Fever
Fever is the result of an immune response by your body to a foreign invader. These foreign invaders include viruses, bacteria, fungi, drugs, or other toxins.
These foreign invaders are considered fever-producing substances (called pyrogens), which trigger the body’s immune response. Pyrogens tell the hypothalamus to increase the temperature set point in order to help the body fight off the infection.
Fever is a common symptom of most infections, and thus a risk factor for fever is exposure to infectious agents. In children, immunizations (such as shots) or teething in may cause low-grade fever. Autoimmune disorders, medication reactions, seizures, or cancers may also cause fevers.
Fever itself is not contagious; however, if the fever is caused by a viral or bacterial infection, the infection may be contagious.
Symptoms of Fever
You have a fever when your temperature rises above its normal range. What’s normal for you may be a little higher or lower than the average normal temperature of 98.6 F (37 C).
Depending on what’s causing your fever, additional fever signs and symptoms may include:
- Muscle aches
- Loss of appetite
- General weakness
High fevers between 103 F (39.4 C) and 106 F (41.1 C) may cause:
Fever in Children
A normal temperature in children is about 36.4C (97.5F) but this does differ slightly from child to child. A fever is usually considered to be a temperature of over 37.5C (99.5F).
You may be concerned that your baby has a fever if they:
- feel hotter than usual to the touch – on their forehead, back or stomach
- feel sweaty or clammy
- have flushed cheeks
Children with a high temperature may develop a febrile seizure, also known as a febrile fit or febrile convulsion, most of which are not serious and may be the result of an ear infection, gastroenteritis, or a respiratory virus (a cold). Less commonly, febrile seizures may be caused by something more serious, such a meningitis, a kidney infection or pneumonia.
Febrile seizures most commonly occur in children aged 6 months to 6 years, and affect boys more often than girls.
The seizure occurs because the body temperature rises too fast, rather than because it has been sustained for a long time.
There are two types of febrile seizures:
1) Simple febrile seizure – the seizure lasts no longer than 15 minutes (in most cases less than 5 minutes) and does not occur again during a 24-hour period.
It typically involves the whole body – a generalized tonic-clonic seizure. Most febrile seizures are of this type. Symptoms – the body becomes stiff and the arms and legs start to twitch, the patient loses consciousness (but the eyes stay open).
There may be irregular breathing and the child may urinate and/or defecate. There may also be vomiting.
2) Complex febrile seizure – the seizure lasts longer, comes back more often, and tends not to affect the whole body, but rather only part of the body.
This type of seizure is a cause for more concern that simple febrile seizures.
In the majority of cases, a child with a febrile seizure does not need treatment. Temperature may be controlled with acetaminophen (paracetamol) or sponging. If necessary an anticonvulsant, such as sodium valproate or clonazepam may be prescribed.
Fever is the temporary increase in the body’s temperature in response to a disease or illness.
A child has a fever when the temperature is at or above one of these levels:
- 100.4°F (38°C) measured in the bottom (rectally)
- 99.5°F (37.5°C) measured in the mouth (orally)
- 99°F (37.2°C) measured under the arm (axillary)
An adult probably has a fever when the temperature is above 99 – 99.5°F (37.2 – 37.5°C), depending on the time of day.
Fever Treatment in Children
If your child has a fever, it’s important to keep them hydrated by giving them plenty of cool water to drink. Babies should be given plenty of liquids, such as breastmilk or formula. Even if your child isn’t thirsty, try to get them to drink little and often to keep their fluid levels up.
To help reduce your child’s temperature you can also:
- keep them cool if the environment is warm – for example, cover them with a lightweight sheet (but they should be appropriately dressed for their surroundings)
- keep their room cool – 18°C (65°F) is about right (open a window if you need to)
Sponging your child with cool water isn’t recommended to reduce a fever.
Fever Treatment in Adults
The most common treatments for fever include over-the-counter drugs such as acetaminophen (Tylenol) and nonsteroidal anti-inflammatory drugs such ibuprofen (Advil, Motrin) and naproxen (Aleve). Children and teens should not take aspirin because it’s linked to condition called Reye’s syndrome.