Food poisoning, also called foodborne illness, happens when you get sick from eating or drinking something contaminated with germs or toxins. It can be caused by bacteria, viruses, parasites, or chemicals. Symptoms can start quickly after eating, or they may take hours to days depending on the cause. Most mild cases improve with fluids, rest, and time. However, food poisoning can sometimes cause dehydration or serious infection, especially in older adults, pregnant people, yo