Certain types of food poisoning can even kill. Most food contamination is caused by organisms that occur naturally in foods. The organisms responsible for the most contamination are bacteria. Bacteria are everywhere, even in the human body. Fortunately, only a few types of bacteria are harmful.
Viruses are also responsible for some food-borne illnesses.
Still another source of contamination is mold. Molds vary in their ability to cause illness, but some are deadly. Some contamination, such as spoiled fruit, is easy to see and smell. Contamination, however, is not always easy to detect. It's true that you may buy food that contains bacteria or viruses or molds and not even know it.