Food poisoning can be from chemical or biological sources. If we eat food that contains harmful chemicals, or biological toxins (poisons) from plants, animals or microorganisms, that food can make us sick. Some common sources of food poisoning are caused by contaminants already in the food when the raw materials are harvested, for example:

• Bacterial toxins produced by bacteria such as Clostridium botulinum and Clostridium perfringens, which are commonly found in the natural environment, e.g. in soil.
• Chemical toxins, e.g. insecticides sprayed onto growing crops.
• Heavy metals, e.g. lead and mercury, particularly in fish caught near chemical processing facilities.
• Certain toxic plant tissues, e.g. poisonous mushrooms.
• Toxic animal tissues, e.g. the poison glands of certain fish, crabs, etc.

Chemical food poisoning can also occur if foodstuffs have been in contact with toxic chemicals during food production, processing, storage and handling.

The symptoms of food poisoning can range from mild headache to severe flu-like symptoms. The most common signs and symptoms are nausea, stomach cramps, diarrhoea, fever, chills and vomiting. A person with food poisoning may have any combination of these symptoms depending on the cause or the agent involved. The illness may begin from 1 to 72 hours after eating the food.