Topic 1 Food hazards and foodborne illness
A food can look good, smell good and still make the person who eats it ill. This topic explains what can contaminate food, why microbes grow so fast and which ones cause the most food poisoning.
What a food hazard is
A hazard is anything in a food that can harm the health of the person who eats it. There are four types:
- Biological: bacteria, viruses and parasites. According to the WHO, most foodborne illnesses are caused by infections with bacteria, viruses or parasites, and also by toxic chemicals.
- Chemical: traces of cleaning products or insecticides, substances that pass from the packaging into the food, or frying oil that has broken down badly.
- Physical: pieces of glass, metal, plastic, bones, hairs, jewellery or a plaster.
- Allergens: ingredients that can cause serious reactions in people with allergies, even in very small amounts. They have their own topic (topic 5).
We say a food is contaminated when it carries one of these hazards. You can almost never see contamination: a chicken with Salmonella looks the same as one without it.
Bacteria multiply: time and temperature
Many bacteria, if they find food, moisture and a warm temperature, split in two again and again. In a few hours, a few bacteria can become millions. This is why the World Health Organization (WHO) talks about a danger zone between 5 °C and 60 °C: in this range they multiply fastest. So food must be either cold or hot, and spend as little time as possible at room temperature.
- Cold slows down most bacteria, but does not kill them. When you take the food out of the fridge, they start multiplying again.
- Enough heat (cooking well, right to the centre of the food) kills most of them.
- Some bacteria produce toxins, poisonous substances that stay in the food. The toxins of Staphylococcus aureus and one of the toxins of Bacillus cereus resist heat: reheating a contaminated dish does not make it safe.
- Others, such as Bacillus cereus, form spores, resistant forms that survive cooking and become active again if cooked food is left at room temperature.
Foodborne illness
When someone becomes ill from eating contaminated food, we call it a foodborne illness. When the cause is a microbe or its toxin, it is often called food poisoning. The most common symptoms are vomiting, diarrhoea, stomach ache and sometimes fever, but some cases can be very serious. When several people become ill after eating the same food, we call it an outbreak.
According to the WHO, the people most at risk of becoming seriously ill are pregnant women, babies and young children, older people and people with weak immune systems. Think of them when you work in a school canteen, a care home or a hospital.
The microbes worth knowing
| Microbe | Where it usually appears | How to prevent it |
|---|---|---|
| Salmonella | Eggs, poultry and pork, sauces made with raw egg. | Cook well, do not crack eggs over food that will not be cooked, keep food cold, wash your hands after touching eggs or raw meat. |
| Campylobacter | Raw or undercooked chicken; it passes easily to other foods through chopping boards, knives and hands. | Cook chicken well and avoid cross-contamination. |
| Listeria monocytogenes | Ready-to-eat foods kept cold for a long time: raw-milk cheeses, smoked fish, sliced cold meats, pâtés. | Respect use-by dates, clean the fridge and slicers well. It grows even in the fridge. Very dangerous during pregnancy. |
| Toxin-producing Escherichia coli | Undercooked minced meat, raw milk, contaminated raw vegetables and sprouts. | Cook minced meat well, wash vegetables, avoid cross-contamination. |
| Staphylococcus aureus | Lives on people’s skin, in the nose and in wounds. It passes to foods that are handled a lot and not cooked afterwards (sandwiches, salads, cream cakes). | Hand hygiene, cover wounds, do not cough or sneeze over food and keep food cold. Its toxin resists heat. |
| Bacillus cereus | Cooked rice and pasta left at room temperature. | Cool quickly and keep in the fridge; do not leave cooked rice on the worktop for hours. |
| Norovirus and hepatitis A virus | Ill people who handle food; raw molluscs (such as oysters and mussels) from contaminated waters. | Do not work with food if you have vomiting or diarrhoea, wash your hands and buy molluscs with health guarantees. |
| Anisakis | A parasite of sea fish eaten raw or undercooked (sushi, anchovies in vinegar, ceviche). | Cook fish well or freeze it first as the rules require (topic 4). |
You do not need to memorise the names. What matters is recognising risky situations: raw meat and eggs, food eaten without cooking, large quantities that cool slowly, ill people in the kitchen and food that spends hours out of the fridge.
Chemical and physical hazards in everyday work
- A cleaning spray used near an uncovered salad.
- A cleaning product poured into a water bottle: someone may drink it or add it to a stew.
- A broken glass in the preparation area: you must remove everything the glass may have reached.
- Staples, rubber bands, labels or bits of packaging that fall into food.
- Rings, earrings or a plaster lost in the dough.
All of them are avoided by keeping things tidy, storing chemicals away from food and in their original containers, and following good personal practices (topic 2).
Sources for this topic
- Food safety (fact sheet). World Health Organization (WHO).
- Five keys to safer food manual. World Health Organization (WHO).
- Salmonella (non-typhoidal) (fact sheet). World Health Organization (WHO).
- Listeriosis (fact sheet). World Health Organization (WHO).
- Campylobacter (fact sheet). World Health Organization (WHO).
- E. coli (fact sheet). World Health Organization (WHO).
- Regulation (EC) No 853/2004 laying down specific hygiene rules for food of animal origin (Annex III, Section VIII, Chapter III, Part D: parasites in fishery products). European Parliament and Council of the EU · EUR-Lex.
- Guidance document on food handler training (ratified on 21/07/2010) (in Spanish). Spanish Agency for Food Safety and Nutrition (AESAN).
- Staphylococcal enterotoxin poisoning (fact sheet, 27/06/2022) (in Spanish). Spanish Agency for Food Safety and Nutrition (AESAN).
- Bacillus cereus poisoning and food infection (fact sheet) (in Spanish). Spanish Agency for Food Safety and Nutrition (AESAN).
Nuvola Studio’s own text, based on these sources. Reviewed on 26/10/2026. If you spot a mistake, write to us at delantal@nuvolastudiogroup.com.