Food Safety and the Different Types of Food Contamination

Learn about the three types of food contamination, which can easily occur in a commercial kitchen: biological, chemical and physical.
October 17, 2022

Food contamination happens when something gets into food that shouldn’t be there, rendering it unsafe to eat. Contaminated food can have dire consequences for the person who eats it, and for the business who sold it.

There are three types of food contamination: biological, chemical and physical contamination. Serving contaminated food can lead to food-borne illness outbreaks, allergic reactions and injuries. Food Handlers must be aware of the risks of food contamination, as well as complete training to handle food safely, practise good personal hygiene and prevent cross-contamination, which is the transfer of contaminants, to protect customers and the food establishment. 

Learn more about each type of contamination, how they happen, and ways to prevent them.

Biological contamination

Biological contamination is when disease-causing bacteria or other harmful microorganisms called “pathogens” contaminate food and are consumed; it is a common cause of food poisoning and food spoilage. Bacteria are small microorganisms that split and multiply very quickly. In conditions ideal for bacterial growth, one single-cell bacteria can become two million in just seven hours.

Certain types of bacteria also produce bacterial toxins in the process of multiplying and producing waste. Bacterial toxins can be very dangerous. In fact, botulinum, the bacterial toxin that causes botulism, is the most potent natural poison known.

It's important to remember that all foods can harbour dangerous pathogens. Norovirus, for example, doesn't grow or multiply on food, but it can survive for days or even weeks on any type of food and is a leading cause of food-borne illness in Australia.


Certain foods are more vulnerable to biological contamination than others because they provide everything bacteria need to survive and multiply — food, water and neutral acidity (pH). These are called high-risk foods.

When high-risk foods are left in the Temperature Danger Zone (5ºC – 60ºC) for too long, Food Handlers provide the other conditions bacteria need to grow — time and the right temperature. To slow down bacteria growth and minimise the risk of biological food contamination, Food Handlers must always follow safe food handling practices:

  • Keep high-risk foods (e.g. meat, poultry, seafood, eggs, dairy) out of the Temperature Danger Zone.
  • Properly purchase, store, thaw, prepare, cook and serve high-risk foods.
  • Follow a regular cleaning and sanitising schedule for all food contact surfaces and equipment, and ensure you are following the correct steps for cleaning and sanitising.
  • Maintain high standards of hygiene and sanitation of the premises, including personal hygiene for all staff.

Chemical contamination

Chemical contamination occurs when chemicals get into food. Common sources of chemical contamination in a commercial kitchen include:

  • Kitchen cleaning agents: Never keep food stored in the same place as your cleaning chemicals, and always use cleaning products designed especially for kitchen use.
  • Unwashed fruits and vegetables: Pesticides and fungicides on fruits and vegetables can be harmful if ingested, so it’s important to properly wash all fruits and vegetables before preparing them.
  • Food containers made from non-food grade plastics: Single-use items like plastic containers are not designed to be reused again and again. Always store food in containers that are food grade and specially designed for reuse.
  • Pest control products: Pest control products are extremely hazardous. Always store these products away from food items and never use these products in areas where food is being prepared.
  • Kitchen equipment: Equipment with moving parts, such as slicers and mixers, may need regular oiling. Always use food-safe oil to prevent chemical residues from contaminating food.

Physical contamination

Physical contamination happens when physical objects enter food. Common sources of physical contamination include:

  • Hair: Always wear hair neatly tied back and wear a hairnet if possible.
  • Glass or metal: Cracked or broken crockery and utensils should be thrown away, as well as any food that might have come into contact with it.
  • Pests: Pests — such as mice, rats and cockroaches — leave droppings (urine, saliva, fur, faeces) that can contaminate food. Pests themselves can also make their way into food.
  • Jewellery: It is not recommended to wear jewellery when handling food. In some regions, it may be restricted by local laws or regulations.
  • Dirt: Because dirt is so small, it’s easy not to notice it. Dirt often gets into food via unwashed food and vegetables.
  • Fingernails: Always keep nails short and clean to prevent contamination. Avoid wearing fake nails as these can easily fall off and contaminate food.


In a food setting, cross-contamination refers to the transfer of contaminants from a surface, object or person to food. This can happen in many different ways. Common causes of cross-contamination include:

  • Clothing: Dirty clothes can transport bacteria from one place to another. If possible, clothing should be replaced when moving from one work area to another. You should also thoroughly wash your face and hands. This is especially important when working with high-risk foods or when preparing allergen-free meals.
  • Utensils: Different utensils should be used to prepare different types of foods. For example, you should never use the same chopping board or knife to prepare raw meat and ready-to-eat foods.
  • Food Handlers: Coughing, sneezing or even touching your face or hair before handling food can cause cross-contamination. Washing hands regularly when handling food is essential. Display the AIFS Correct Hand Washing Method Poster around all hand washing stations to remind staff of the proper steps to take.
  • Pests: Flies, cockroaches, mice and rats carry harmful bacteria, which they can transport from one place to another. Pest control is vitally important in the workplace when it comes to preventing cross-contamination. Learn more about how to effectively prevent pests from getting into your food business with the AIFS Guide to Pest Prevention and Control.
  • Raw food storage: Cross-contamination frequently occurs when raw food comes into contact with cooked or ready-to-eat food. If this happens, it's fair to assume the cooked or ready-to-eat food has become contaminated. Raw food should always be covered and stored below ready-to-eat food in the refrigerator to prevent this type of contamination.
  • Waste control: Garbage should be stored and sealed correctly to prevent cross-contamination. It should always be stored away from other items in the kitchen to ensure it never comes into contact with food during preparation. Regular cleaning and sanitising of waste bins should also be carried out to minimise the risk of pest infestation.

Preventing food contamination

As a food handler, it's important to remember that contamination can happen many ways, and sometimes in unexpected or overlooked places. The best way to prevent food contamination from happening in a food business is through food safety training and education. Food Handlers must be trained in fundamental food safety concepts and practical skills, such as:

  • Safe cooking temperatures
  • Proper storage and preparation of high-risk foods (also called 'potentially hazardous foods')
  • Effective cleaning and sanitising techniques
  • The importance of personal hygiene and their legal responsibilities with regards to food safety

AIFS provides online food safety training for all levels of responsibility in a food business or organisation, including the nationally recognised online Food Handler Course and Food Safety Supervisor Course.

Find the Food Safety Course for your needs and start your training today! If you have any questions about which training is right for you or your team, contact us and we’ll be more than happy to assist.