What is the most common symptom of a foodborne illness?

The most common symptom of a foodborne illness is diarrhea. This symptom often occurs because many pathogens, such as bacteria and viruses, target the gastrointestinal tract, leading to inflammation and resulting in the body expelling waste more rapidly than usual. Diarrhea is the body's way of trying to rid itself of the harmful organisms it has ingested, which is why it frequently presents as the primary symptom in many foodborne illnesses.

While nausea, headache, and fever can also occur with foodborne illnesses, they are typically less prevalent than diarrhea. Nausea may accompany diarrhea but is often a secondary symptom rather than the main issue. Headaches can arise due to dehydration from diarrhea or as a response to certain infections, and fever may indicate a more serious infection but is not as universally common as diarrhea across the spectrum of foodborne illness symptoms.