Fever, also called hyperthermia, is a high body temperature that is often a sign of illness. Typically, your body temperature is very close to 98.7 degrees Fahrenheit (or 37.0 degrees Celsius). You can check your temperature with a thermometer if you think you have a fever. There are many types of thermometers and it is important to learn how to use the thermometer correctly.
You may feel tired, weak, and tired when you have a fever. A low temperature below 100.4 degrees Fahrenheit is generally not a problem, but if your body temperature is above 100.4 degrees Fahrenheit, it is considered a high fever and you should talk to your healthcare provider about it .
If you have a fever, your healthcare provider may recommend medications to lower the fever and may also prescribe treatment for the illness that is causing your fever.
Fever can develop quickly or slowly, intermittently or continuously. The pattern often depends on the cause. The temperature can range from subfebrile (98.7 to 100.4 degrees) to a high temperature above 100.4 degrees.
While a high body temperature can cause symptoms , the underlying condition that caused the fever can also cause symptoms, making you feel very unwell. You may find that some of the symptoms are as severe as your temperature, while others do not change with a fever.
Common symptoms of fever include:
- Shaking chills
- Tired and sore eyes
- Decreased appetite
Depending on the cause of the fever, you may experience accompanying symptoms such as a sore throat, runny nose, earache, indigestion, rash, cough, muscle pain, or painful urination.
Untreated fever can be associated with serious health problems, especially in young children. A severe fever is much more likely to cause serious problems than a mild fever.
Complications of fever include:
- Dehydration – Fever is associated with fatigue, decreased fluid intake, and sweating, all of which can lead to dehydration.
- Confusion : You may have less concentration and confusion when you have a fever.
- Hallucinations – A very high temperature can cause a person to experience a fluctuating sleep-like state that can lead to confusing hallucinations, especially when you are not sure whether you are asleep or awake.
- Loss of consciousness : In some situations, especially when dehydrated, a person may pass out due to fever.
- Heatstroke – High core body temperature can have the same effects as heatstroke, in which a person is exposed to high temperatures outside.
- Febrile seizures : Changes in body temperature affect the functioning of proteins and neurotransmitters in the body, which can cause a sudden generalized tonic cone seizure. This complication is more common in young children.
Infections are the most common causes of fever . There are a number of other illnesses that also cause fever. Fever is caused by an inflammatory response in the body that helps fight infection and disease.
Common infections that cause fever include:
- Malaria : a parasitic infection that causes cyclical fevers. Spread by mosquitoes.
- Q fever : a bacterial infection that causes a severe fever. It is transmitted to humans from animals such as cattle and sheep.
- Yellow fever – a viral infection that causes prolonged heat and liver damage. Spread by mosquitoes.
- Scarlet fever – An infection that causes a high fever, rash, and swelling of the tongue. It is caused by bacteria group A streptococcus , the same bacteria that cause a sore throat.
- Dengue fever : a viral infection that causes internal bleeding and fever. It is transmitted by mosquitoes and is caused by the Aedes aegypti or Aedes albopictus viruses.
Most infections can cause a fever. In general, bacterial and parasitic infections are the most common cause of severe fever. Infections that spread throughout the body and cause sepsis usually cause a high fever.
Non-infectious causes of fever.
Inflammatory conditions that affect the immune system can cause fever, even if they are not associated with an infection.
Illnesses that cause fever include:
- Autoimmune diseases such as lupus , sarcoidosis , and arthritis.
- Non-infectious encephalitis (inflammation of the brain)
- A ruptured appendix (which often begins as an infection)
- Heat exhaustion and heat stroke
Certain medications can cause fever, such as cephalosporin and aldomet (methyldopa). Antidepressants can trigger serotonin syndrome, a dangerous reaction consisting of muscle stiffness and fever. Medications like methamphetamine can also cause a fever.
Getting dressed, which is common for babies wrapped in blankets or in too much clothing, can also cause a fever.
How the fever starts
When you have an infection, one of the ways your immune system reacts to germs is by raising your body temperature, making it harder for germs to survive. Immune cells, which are activated in response to infections, secrete immune proteins called cytokines that raise body temperature .
Several other diseases that cause inflammation can cause fever due to similar immune mechanisms.
There are several ways to monitor your body temperature or your baby's body temperature. Each method requires a device specifically designed for that method of measuring body temperature.
Results can vary by approximately one degree depending on the part of the body being examined. Regardless of which method you use, you will get a general idea of its temperature. But it is important to follow the instructions and tests for the method you are using.
Methods for measuring body temperature include:
Oral (by mouth) : The most widely used thermometers measure temperature through the mouth. For this method, you need to hold the thermometer under your tongue for about three minutes before reading the temperature.
Tympanic (in the ear) : The tympanic thermometer is held against the opening of the ear. To avoid injury, the thermometer should be placed at the entrance of the ear canal and not pushed deep into the canal.
Pain or discomfort is a sign that the thermometer is too deep in the ear canal or it could be a sign of an ear injury. After about three minutes, you can read the temperature on the thermometer.
Temporary (forehead or temple) : This type of temperature measurement uses a device that is placed on the forehead. The device can change color based on body temperature or give digital readings. It is the least invasive and least accurate method of measuring body temperature.
Armpits : You can check the temperature in your armpits by placing a thermometer under your armpit. This is not a common method, especially since children often wriggle and squirm during the process.
Rectal : This method is generally used for babies because it is the most accurate. Babies may not be able to cooperate with other methods. As with other methods, leave the thermometer for a few minutes to get an accurate reading.
Be sure to clean the thermometer, preferably with an alcohol wipe, between each use. It is recommended that you repeat the temperature measurement to make sure you or your child have a fever.
If you have a fever, your healthcare provider can perform several tests to determine the cause. You may need blood tests that can identify inflammatory cells and can often differentiate between infections and inflammatory conditions.
Blood culture, urine culture, or throat culture can be used to grow an infectious organism in a laboratory setting, facilitating direct treatment.
Sometimes imaging tests are needed if there is a concern that you may have an abscess (closed infection), a ruptured appendix, or cancer.
Fever can usually be treated with over-the-counter antipyretic medications such as Advil or Motrin (ibuprofen) , Tylenol (acetaminophen) . These medications can generally lower your body temperature and make you feel more comfortable for about four hours. Some of the other symptoms you may experience, such as a sore throat, nausea, or a rash, are unlikely to improve after treating the fever.
It is recommended that you consult with your healthcare professional and find out how long to wait before going to your appointment. For example, your healthcare provider may ask you to come in if you still have a fever after a week. If you have a medical condition such as cancer, your healthcare provider may want you to be seen even after a day or two of fever.
Some strategies that can help lower your temperature include staying hydrated and applying a cold towel to your hands or forehead for comfort.
Children can have a fever all day and feel fine the next day. Many childhood infections clear up quickly on their own. However, it is still a good idea to speak with your child's pediatrician for guidance on when to bring your child and how long to leave him out of school.
If you are treating a child with a high fever, there are several important things to keep in mind:
- Never give aspirin or baby aspirin to children under 18 years of age. This can cause a serious condition called Reye's syndrome .
- Children younger than 6 months should not take Motrin or Advil ( ibuprofen ).
- Antipyretic drugs should not be given to children younger than 2 months.
- Never place a child or anyone else in an ice or alcohol bath to lower the temperature. This is not necessary and it can be dangerous to lower your body temperature too quickly.
Fever is especially worrisome for young children. This is because babies have fragile temperature regulation and can experience serious consequences as a result of fever. Young babies should seek medical attention in high temperatures.
- Babies under 3 months of age: Call your doctor or seek immediate medical attention if the temperature exceeds 100.4 degrees Fahrenheit.
- Babies 3 months to 3 years of age: Call your doctor or seek immediate medical attention if the temperature is above 102.2 degrees Fahrenheit.
The use of alcohol wipes, rubbing alcohol, or an alcohol bath has been used as a home method to reduce fever. This is dangerous and is not recommended. Alcohol can be dehydrated and toxic, so it is important never to consume alcohol as a fever remedy.
Get the word of drug information
Fever is the body's way of fighting infection. Fever is a sign that you have an illness that needs treatment.
In most cases, the infections that cause the fever are not serious and go away on their own after a few days of rest. However, fever can be a sign of a more serious problem, so be sure to call your doctor if you have a high fever, prolonged fever, or if your young child has a high fever.