Fever
Fever is a common health symptom that can happen for many reasons. Viruses, bacteria, or other germs entering the body most often cause fever. Sometimes, other factors like inflammation, certain medicines, or autoimmune diseases can lead to a rise in body temperature.
While many people think of fever as a problem, it is actually the body’s way of fighting off an illness. Fever acts as a sign that something isn’t right, so paying attention to why a fever happens is important for understanding your health.
Definition of Symptom
A symptom is a noticeable change in the body or mind that shows something may be wrong. It is something a person experiences, such as pain, tiredness, or fever. Symptoms help doctors understand what type of illness or condition might be present.
Fever means the body temperature is higher than usual. For most people, normal body temperature is about 98.6°F (37°C). An elevated temperature usually means the body is fighting off something, like an infection.
How to Measure Body Temperature
| Method | Typical Normal Range |
|---|---|
| Mouth (oral) | 97.6°F – 99.6°F |
| Rectal thermometer | 98.6°F – 100.4°F |
| Armpit (axillary) | 96.6°F – 98.6°F |
The hypothalamus, located in the brain, controls the body’s temperature. When the hypothalamus senses a problem, such as germs in the body, it raises the temperature and causes a fever. Common signs of an elevated body temperature include:
- Feeling hot or flushed
- Chills or shivering
- Sweating
- Headache or muscle aches
A fever is not a disease, but a sign that the body is responding to a problem. If the fever is very high or lasts several days, it may need more attention from a healthcare provider.
Possible Causes/Diseases Condition
Many different health conditions can trigger a fever. Most often, the body responds to an infection. Viruses, bacteria, or even fungi can cause these infections.
Common Viral Infections
- Influenza (flu)
- Common cold
- COVID-19
- Rotavirus (common cause of stomach flu in kids)
Common Bacterial Infections
- Pneumonia
- Urinary tract infection (UTI)
- Ear infection
- Gastroenteritis (sometimes caused by bacteria)
Some serious diseases and conditions can also cause fever:
- Lupus: An autoimmune disease where the body attacks its own tissues.
- Rheumatoid Arthritis: Another autoimmune disorder that can cause inflammation and fever.
- Cancer: Certain cancers, like lymphoma, may first show up as a low-grade, ongoing fever.
Below is a table showing some common causes and examples:
| Cause Type | Example Conditions |
|---|---|
| Viral Infection | Flu, common cold, COVID-19, rotavirus |
| Bacterial Infection | Pneumonia, UTI, ear infection, gastroenteritis |
| Autoimmune Disease | Lupus, rheumatoid arthritis |
| Other | Cancer (like lymphoma) |
In many cases, stomach flu (gastroenteritis), whether viral or bacterial, leads to fever. Symptoms of the underlying disease often help narrow down the cause. People can develop a fever from both simple and serious conditions, so the cause can range widely.
Other Non-Disease Causes
Not all fevers come from infections or illnesses. Sometimes, people can develop a fever-like rise in body temperature from other sources. Environmental factors like hot weather or high humidity can cause the body to overheat. This is not a true fever but can feel similar. Heat exhaustion and sunburn are common situations where this might happen.
Dehydration can also raise body temperature. When the body does not have enough fluids, it cannot cool down properly, leading to increased heat and sometimes mild fever-like symptoms. Some medicines and drugs can cause side effects, including fever or chills. These reactions may come with body aches or muscle aches. Here are some non-disease causes of fever-like symptoms:
| Cause | Example Symptoms |
|---|---|
| Heat exhaustion | Weakness, chills, sweating |
| Sunburn | Skin redness, mild fever |
| Dehydration | Dry mouth, headache |
| Drug reaction | Rash, chills, aches |
Physical trauma or injury can also trigger a rise in body temperature, especially if there is swelling or inflammation. This response helps the body recover but is not due to an infection.
How It Causes the Symptom
The body’s internal “thermostat” raises its temperature above normal during a fever. This thermostat sits in the hypothalamus, a part of the brain. When viruses, bacteria, or other germs enter the body, the immune system reacts and releases chemicals called pyrogens. These pyrogens can come from germs or from the body itself. Here’s what happens step by step:
- The body senses an infection or illness.
- White blood cells release pyrogens into the bloodstream.
- Pyrogens make the hypothalamus set the body temperature higher.
- The person feels cold and may start to shiver as the body works to heat up.
Fever can appear as a low-grade fever (slight temperature rise) or a high fever (much higher temperature) depending on how strong the body’s response is.
| Fever Type | Typical Temperature Range |
|---|---|
| Low-Grade Fever | 99–100.9°F (37.2–38.2°C) |
| High Fever | 103°F (39.4°C) or higher |
Common fever symptoms include sweating, chills, and feeling tired. Some people may also have muscle aches or headaches. Both fever in adults and in children act as a sign that the body is fighting something off. The term pyrexia is another word used to describe a fever.
Possible Complications
A fever is usually not dangerous by itself, but it can sometimes lead to health problems. People may experience symptoms such as vomiting, nausea, and abdominal pain. These can cause discomfort and may lead to dehydration if fluids are not replaced.
Some people with fever may notice a rash, which can be a sign of a more serious infection. When a fever is very high or lasts for a long time, more severe symptoms like a stiff neck, confusion, or a severe headache can appear. These symptoms may suggest problems like meningitis and need quick medical attention. Children, especially those between 6 months and 5 years old, can have febrile seizures. These are convulsions caused by a rapid rise in body temperature.
Although most febrile seizures are brief and not harmful, they can be scary for parents. Rarely, if a fever stays high or is not treated, there may be more serious risks. These include organ damage, very severe infections, and in extreme cases, seizures or coma. Below is a table with some complications and their signs:
| Complication | Possible Signs/Symptoms |
|---|---|
| Dehydration | Dry mouth, thirst, low urine |
| Febrile seizures | Shaking, brief loss of awareness |
| Rash | Spots, redness on skin |
| Stiff neck | Neck pain, trouble moving neck |
| Confusion | Trouble thinking, disorientation |
| Severe headache | Intense pain in head |
| Abdominal pain | Belly discomfort, cramps |
When to Seek Medical Attention
Sometimes, you can manage a fever at home. However, some situations require medical help. Adults should contact a healthcare provider if:
- The temperature reaches 103°F (39.4°C) or higher
- Fever lasts longer than three days
- Other serious symptoms appear, such as chest pain, trouble breathing, confusion, or a stiff neck
Children and infants need attention for these signs:
- Any fever in infants under 3 months old
- Fever over 102°F in children between 3-12 months
- Persistent vomiting, a rash, or if the child seems unusually sleepy or irritable
You can treat fever with medicine such as:
- Acetaminophen
- Ibuprofen
- Aspirin (only for adults)
Follow the dosing instructions when using these medicines. Do not give aspirin to children or teens because it can cause a rare but serious illness called Reye’s syndrome. Seek immediate care if a fever comes with:
- Severe headache
- Rash
- Trouble thinking clearly
- Difficulty breathing
- Chest or stomach pain
If you are unsure when to get help, call a health provider or visit a clinic.
