What is food poisoning?
Food poisoning is an illness you get from eating food that has harmful germs or poisons in it. Poison is also called toxin.
Common signs: stomach pain, vomiting, loose motions, sometimes fever. They can start within an hour or after a few days. Most healthy people get better in a day or two. Babies, old people and sick people can get very ill, so they need a doctor quickly.
There are four kinds: bacterial, viral, chemical and natural-toxin. Learn the cause and you can learn the cure.
Bacterial food poisoning and prevention
Bacteria are tiny living things. On warm, moist food they can split in two every 20 minutes. Two types of harm:
- Infection type: we eat the live bacteria, and they hurt the gut. Examples: Salmonella (eggs, chicken), E. coli (undercooked meat, dirty water), Campylobacter (raw chicken).
- Toxin type: bacteria make poison in the food before we eat it. Examples: Staphylococcus aureus (from skin, nose, cuts; found in sweets and cream foods) and Clostridium botulinum (badly canned food). Reheating does not always remove the poison.
Prevention:
- Wash hands. Cover cuts.
- Keep raw and cooked food apart.
- Cook to at least 75 °C in the centre.
- Keep cold food at 5 °C or less and hot food at 60 °C or more.
- Do not leave food out more than 2 hours.
Viral food poisoning and prevention
A virus is even smaller than bacteria. It cannot grow on food. It needs a living body. So food only carries it, like a taxi.
- Norovirus: causes vomiting and loose motions. Spreads through hands and shellfish from dirty water.
- Hepatitis A virus: attacks the liver. Spreads through dirty water and raw food touched by dirty hands.
Prevention: wash hands with soap for 20 seconds, especially after the toilet. Drink boiled or clean water. Cook shellfish well. Stay away from kitchens when you are sick. Vaccine is available for hepatitis A.
Chemical food poisoning and prevention
Chemical food poisoning happens when a harmful chemical gets into food. It often acts fast.
- By mistake: cleaning liquid or insect spray kept in a cold-drink bottle.
- From pots: acidic food kept in a bad metal pot can pick up metal.
- From farms: too much pesticide, or no waiting time before harvest.
- From industry: waste with heavy metals (lead, mercury, cadmium) reaching water and fish.
- Too many additives: more than the legal limit.
Prevention: store chemicals away from food in marked containers; use food-grade pots and bottles; wash and peel produce; buy from licensed sellers; follow legal limits.
Natural-toxin food poisoning and prevention
Some living things make poison inside themselves. These natural toxins are not germs. Many cannot be destroyed by cooking.
- Plants: some wild mushrooms, green or sprouted potatoes (solanine), some raw beans, bitter cassava if not prepared well.
- Animals: puffer fish (tetrodotoxin) and some shellfish when sea algae bloom.
Prevention: eat only plants and fish you know are safe; do not pick wild mushrooms; cut off green parts and sprouts of potatoes; soak and cook beans well; buy fish from trained sellers. Remember: not a germ, so heat does not always help.
Try it
In the 3D, pick each kind and watch the dots. For bacteria, press Step 2 and count how the germs double. Press Prevent and see the shield. At home, look at your kitchen: where are the cleaning liquids kept? Are they far from food and in their own bottles? Write down one change.
Key formulas and definitions
- Four kinds: bacterial, viral, chemical, natural toxin
- Bacteria doubling: N = N₀ × 2ⁿ (n = time ÷ 20 min)
- Safe zones: cold ≤ 5 °C, hot ≥ 60 °C, cook centre ≥ 75 °C
- Virus: does not grow on food, spread by hands and water
Worked examples
1. One bacterium on a cake doubles every 20 minutes. How many are there after 2 hours?
2 hours = 120 min = 6 doublings. N = 2⁶ = 64.
2. A cook has a cut finger and makes cream sweets. Later people get vomiting within 4 hours. Which kind of poisoning is this and why?
Bacterial, toxin type. Staphylococcus from the cut grew in the cream and made a toxin. Fast onset (1 to 6 hours) shows a pre-made toxin.
3. A group eats raw oysters from dirty water and gets vomiting after two days. Which kind is likely, and what could prevent it?
Viral (norovirus). Prevention: buy shellfish from clean water and cook it well, and keep sewage out of water.
4. Classify each: (a) green potato, (b) cleaner in a cold-drink bottle, (c) undercooked chicken, (d) dirty hands spreading hepatitis A.
(a) natural toxin, (b) chemical, (c) bacterial, (d) viral.
5. Why does boiling fix some food poisoning but not mushroom poisoning?
Boiling kills germs, but the mushroom poison is a chemical made by the mushroom. Heat does not break it down.
Common mistakes
- Thinking heat always makes food safe. Some bacterial and natural toxins survive cooking.
- Thinking viruses grow on food. They only ride on it.
- Storing chemicals in food or drink bottles.
- Tasting or smelling food to check if it is safe. Many germs and toxins have no taste or smell.