It would be difficult to list all the causes of fever and nausea because there are thousands of them. Fever actually helps in deciding what might be resulting in nausea, or the urge to vomit, because it eliminates certain things from the list. In general, the most common causes of nausea and a fever are gastrointestinal viral illnesses and parasitic, amoebic or bacterial gastrointestinal infections. Sometimes people feel nauseous when they have a fever even if they don’t have any form of stomach infection.
The classic stomach flu, which is often caused by a class of viruses called rotaviruses, can cause fever and nausea concurrently in some people. These are seldom the only two symptoms of this illness. Many people also develop stomach pains, cramping, diarrhea and/or vomiting, too.
Though most people survive the stomach flu and recover from the worst of its symptoms in a few days, if excessive vomiting or diarrhea occurs, especially with fever, this can lead to dehydration, and the risk is greater for the very young, the very old, or the medically vulnerable. Continued vomiting or diarrhea for more than half a day should be reported in medically vulnerable patients, and people who are ill for more than a day with stomach flu symptoms should also contact their doctors, particularly if fever is above 100.4 degrees F (38 degrees C).
Another common cause of fever and nausea is amoebic, parasitic or bacterial infections, often resulting from consuming contaminated foods. Simple cases of food poisoning may seem similar to the stomach flu. More severe illness may cause not only fever and feelings of nausea for several days, but pronounced vomiting and/or diarrhea. Some of these infections linger, creating stomach upset for long periods of time, and they are especially concerning when stomach upset gets paired with a long-lasting fever. Such symptoms are always a good indication to see a physician.
As the body heats up, people can feel sweaty, achy, dizzy, and otherwise uncomfortable. Thus virtually any fever may make people feel disorientated and nauseous. This could happen during any kind of viral or bacterial infection. Usually people can tell the fever, rather than the illness, is directly causing nausea because other symptoms point in a different direction.
There are many other conditions that may cause fever and nausea. A pregnant woman with a virus could have both these symptoms. Some forms of abscesses, stomach cancer, hormonal imbalances, and other conditions could cause these two symptoms, too. Numerous other examples exist. These are usually rare in comparison to the more common and predictable reasons people feel sick to their stomachs and develop fevers.