Fever is a natural part of the body’s defense against illness. Infections are the most common cause of fever, and your temperature may be raised for other reasons, including medication use, inflammation, and other factors. In some cases, a fever can occur without a known cause.
A fever isn’t usually dangerous, and an elevated temperature isn’t even officially considered a fever until it’s above 100.3 degrees Fahrenheit.
This article covers possible causes of a fever so you can better understand the broad range of reasons your body might be reacting in this way — and when medical attention is needed.
How a Fever Happens
Fever is caused by the physiological process of increasing body temperature. This process is mediated by inflammatory cells, chemicals, hormones and brain activity.
Some infectious organisms contain pyrogens, as do many of the body’s immune cells. These are the chemicals that cause fever.
Pyrogens cause fever through a series of events:
- They travel to an area of the hypothalamus (in your brain) called the terminal vascular organ.
- This boosts the production of prostaglandins.
- Prostaglandins raise body temperature through inflammation and vasoconstriction (narrowing of blood vessels to prevent heat loss).
Thermal energy destroys or kills temperature-sensitive pathogens such as viruses (i.e. rhinoviruses) and bacteria (e.g. Streptococcus) This will make you sick. Fever is one of the tools your immune system uses as a weapon against infectious diseases.
In addition to infections, other conditions can cause fever by activating these physiological processes. This can include processes that induce inflammation or processes that directly affect the hypothalamus.
Infections caused by viruses, bacteria, or fungi can make you sick and cause a fever. These diseases are varied and may include the flu, strep throat, Lyme disease, kidney infections, ear infections, appendicitis, and more.
When your immune system recognizes a pathogen as an invader, it may release a pyrogen into your bloodstream. Pyrogens enter the hypothalamus, which is located at the base of the brain and controls your body temperature. Prostaglandins send a message that your body temperature needs to rise, which may keep some pathogens from surviving.
Some pathogens contain pyrogens, which is why some diseases are more likely to cause fever than others. Escherichia coli (E.coli), Pseudomonasand Enterobacter is an example of a pyrogenic pathogen.
The vaccine sometimes causes a mild fever. That’s because they introduce banned pathogens or pathogen-like particles into your body so your immune system can learn to recognize and fight them if you’re exposed to them at some point in the future.
Fever indicates that the vaccine has triggered an immune response (including the action of pyrogens, prostaglandins and the hypothalamus) – just as it was designed.
How exactly do vaccines work?
Inflammation and related diseases
Inflammation is part of the body’s immune response to infection and part of the healing process for many diseases. Some of the chemicals produced by the inflammatory process are pyrogens, so the inflammatory process itself can initiate a chain of events that lead to an increase in body temperature.
Autoimmune and inflammatory diseases are associated with fever, which can come and go as the disease flares and resolves.
Autoimmune diseases associated with fever include:
- Rheumatoid Arthritis
- multiple sclerosis
Autoinflammatory diseases associated with fever include:
- Familial Mediterranean Fever
- Adult Still’s disease
Fever is common in some types of cancer, especially blood cancers such as lymphoma and leukemia. While the reasons for this are unclear, there are several contributing factors. Certain types of cancer cause inflammation, and certain cancer cells may produce pyrogenic substances.
When is a fever a symptom of cancer?
Other inflammatory diseases may involve pyrogens, including:
- Liver Disease
Traumatic brain injury can cause fever if the hypothalamus is affected or if the information from the hypothalamus is disrupted.
Sometimes, blood clots are associated with fever. Surgery can also cause inflammation and inflammation-related fever.
Drugs, illegal drugs and alcohol
Certain medications and medications can trigger a fever.
Serotonin syndrome is a severe reaction that includes many symptoms, including fever. This occurs when monoamine oxidase inhibitors (MAOIs), selective serotonin reuptake inhibitors (SSRIs), and certain antipsychotics are given at very high doses or in combination.
Abstinence from alcohol can lead to imbalances in brain chemicals and, in the most severe cases, delirium tremens (DTs). Fever is just one of many symptoms of DT.
Abuse of amphetamines – including the illicit drugs methamphetamine, ecstasy, and bath salts (synthetic drugs that produce effects similar to cocaine)– It can also raise body temperature.
Fever of unknown origin (FUO)
In some cases, a person develops a fever for no apparent reason.
Fever of unknown origin (FUO) is said to occur when:
- At least twice the temperature was at or above 101 degrees Fahrenheit.
- Fever persists for more than three weeks.
- Fever has no apparent source, even after medical evaluation.
- The patient was not immunocompromised.
Sometimes the cause of the FOU may appear after a while, but usually the cause cannot be found.
When a fever is dangerous
Body temperature usually doesn’t get very high or cause harm, except in rare cases. Still, sometimes a fever can be a sign of serious illness, and a high fever can be dangerous. In these cases, a medical evaluation is important.
If you have persistent or recurring fever, make an appointment to see your doctor.
Some children have febrile seizures when they have a fever, especially if their temperature is over 101 degrees Fahrenheit. Although these events are usually not dangerous and do not cause a seizure, you should call your child’s pediatrician for guidance on treatment.
Get emergency medical help if your child has any of the following symptoms:
- heartbroken cry
- extreme irritability or irritability
- difficulty getting up
- blue lips, tongue or nails
- Raised or sunken soft spots
- stiff neck
- severe headache
- limp, refusing to move
- Difficulty breathing even with a clean nose
- body leaning forward drooling
- Moderate to severe abdominal pain
How to know when a fever is too high
Fever can be scary, but keep in mind that most of them won’t harm you or your child. They are a normal part of your body’s response to disease. If you’re concerned, talk to your healthcare professional to see what you can do to lower the heat or ease any discomfort it causes.
When to see a healthcare provider with a fever