Food poisoning, more accurately called foodborne illness, is caused by the consumption of food contaminated with bacteria, parasites, viruses, or other pathogens (disease causing microbes). It can also be caused by other toxins, including poisonous chemicals and pesticides. Because of this, there is no one type of food poisoning; each different source has different symptoms. The most common symptoms include abdominal cramps, diarrhea, nausea, and vomiting; this is because most foodborne illnesses enter the body through the gastrointestinal tract. It is often unclear whether a disease is foodborne because microbes can be transmitted in a number of ways. While hundreds of types of food poisoning have been identified, many are extremely rare; most are quite mild, but a few can cause serious injury and even death. Healthy people are the safest; those most at risk include the very young, the elderly, and those with already weak immune systems.