What are the four types of food safety hazards? How do you control them?

Table of Contents

Contamination in food can be described as something that should not be there because it could cause harm to the consumers, therefore it is a food safety hazard.

Sources of food contamination can be found at any stage of the supply chain including; food production, food processing, delivery and, service.

Food business operators need to ensure that food handlers have adequate food safety training so that they do not contaminate food. Control measures to prevent contamination should be set out in an effective food safety management system.

It is essential that food handlers are trained to understand the different types of contamination in food and the common sources of contamination so that they can do their part to protect food.

The four types of food safety hazards

  1. Physical contamination
  2. Microbiological or microbial contamination
  3. Chemical contamination
  4. Allergenic contamination

Let’s now look at each type of food safety hazard, where they can come from and how they can be controlled.

Physical contamination

Physical Contaminant

Physical contamination is a foreign object in food that should not be there. Physical contamination can be seen by the consumer and may therefore be distressing.

Whilst physical contamination may not cause food poisoning, physical hazards can be harmful to health. They can cause broken teeth, cuts or choking. Sharp objects such as drawing pins could even perforate the liver.

 Physical contamination can come from a number of places. These include:

  • From the building (plaster, flakes of paint, pieces of brick, broken glass or tiles, screw fixings)
  • From equipment (nuts, bolts, loose screws, pieces of metal)
  • From packaging (pieces of wood, glass, string, staples, elastic bands, plastic, cardboard)
  • From food handlers (hair, nail varnish, fingernails, buttons, chewing gum, pens and lids, earrings and jewellery, plasters)
  • From products (stones, dirt, feathers, bones, eggshell)
  • From pests (bodies, droppings, feathers, eggs). Pests also carry harmful bacteria so are also a microbiological hazard)

Physical contaminants can be controlled in a number of ways, including:

  • Keeping premises and equipment clean and well maintained
  • Checking premises and equipment regularly for faults and defects or even signs of pests. If food handlers find any faults or defects they should report them to their manager/ supervisor immediately.
  • Ensuring repair/building works are not carried out when the premises is preparing/serving food. If repair or building works need to be carried out in food preparation rooms, this should be done when the business is closed and all food should be removed from the area. All surfaces and equipment should be thoroughly cleaned and disinfected before food preparation starts again.
  • Food handlers must be trained and following good personal hygiene practices. These include effective hand washing, wearing protective clothing, tying back long hair, wearing hats/hair nets. Also not wearing jewellery, nail varnish or false nails. In fact, keeping nails clean and short.

Microbiological contamination 

Microbiological Contaminant

Microbiological hazards occur when food becomes contaminated by micro-organisms. These can be found in food, water, soil, the air, humans and animals.

Micro-organisms include bacteria, viruses moulds, yeasts fungi and parasites.

Bacteria are single-celled living organisms that are too small to be seen without a microscope.


The bacteria of concern to food safety are:

  • Pathogenic bacteria – these are the ones that cause food poisoning and food-borne illness
  • Food spoilage bacteria – these cause food to rot, perish or go mouldy

Not all bacteria are harmful, some bacteria are actually used in the food industry such as to make cheese, beer and yoghurt.

Bacteria can come from a wide variety of sources:

  • Raw foods– for example; raw meat products, eggs, poultry, fish and raw fruit and vegetables.
  • Pests and pets can carry bacteria and spread them onto food. If a food business has a pest infestation there will likely be bacteria on food preparation surfaces and equipment. In the case of rodents, this could be through droppings which are visible but also rodents have weak bladders so will likely urinate over the surfaces too.
  • Rubbish if not disposed of and handled correctly can cause bacteria to spread onto food and it may also attract pests.
  • People naturally carry bacteria in large quantities in their intestines and therefore bacteria come out in our faeces. Bacteria are also present on our skin and hair and in our ears, nose and throat and even our clothing. If people do not wash their hands effectively bacteria can end up being transferred to food. The bacteria commonly found on humans is called staphylococcus aureus.
  • Dirt and dust that may contain bacteria can be carried in the air and may contaminate open food.
  • Surfaces and equipment that have not been cleaned properly can also be a source of bacteria.
  • Soil is a source of bacteria that may be present on unwashed fruit and vegetables.
  • Water that has not been treated properly may be a source of bacteria and this could contaminate ready-to-eat fruits and salad items.

Multiplication of bacteria and requirements for growth

Let’s take a look at the things that support the growth of bacteria. Like us, bacteria have certain requirements to survive and grow.

There are 4 conditions that bacteria need, these are:

  1. Time – in the best conditions bacteria can multiply every 10 to 20 minutes
  2. Warmth – bacteria grow between 5°C and 63°C. This temperature range is known as the ‘danger zone’. This means that high-risk foods left at room temperature can result in bacteria growing to unsafe levels. The optimum temperature for bacteria to grow is 37°C. Did you know this is also human body temperature? Food handlers must be trained to control the amount of time high-risk food is in the danger zone.
  3. Moisture – moisture is critical for bacteria to grow. Bacteria will not grow in dry foods.
  4. Food – bacteria only grow in food because they need nutrients to grow. They grow best in protein-based foods such as meats, poultry, seafood, eggs, milk and milk products.

Bacteria multiply through a process called ‘binary fission’. Essentially, in the right conditions, bacteria double in number every 10 to 20 minutes. For example, 1 bacterium becomes 2, 2 bacteria become 4, 4 become 8, 8 become 16 and so on. In just over 1 hour with the right conditions, there could be over 1 million bacteria.

Food handlers play a key role in controlling the conditions that bacteria are provided to stop them from multiplying to unsafe levels and causing food-borne illness or food poisoning.

Toxins and spores

There’s another thing you need to know about bacteria. Most will die when they are subject to unfavourable conditions such as high temperatures or no moisture. But some are able to protect themselves by forming spores.

A spore can be described as a protective coating formed by some bacteria to help them survive adverse conditions such as cooking, drying and chemicals. Spores form when food is left in the danger zone.

Bacteria do not multiply when they are in spore form, but as soon as conditions improve, they emerge from their spores and are free to start multiplying again.

The following bacteria can form spores:

Clostridium perfringens– associated with meat products

Clostridium botulinum – associated with canned, bottled and vacuum-packed products

Bacillus cereus – associated with cooked rice and rice dishes

Some bacteria can also produce toxins. These are poisonous substances produced by some bacteria in the food or in the human gut as the bacteria multiply. Toxins can attack the digestive and nervous systems and result in vomiting, diarrhoea and even death.

Toxins are heat resistant and so will not be destroyed by cooking. It is therefore essential to take steps to prevent toxins from being produced in food in the first place. This means controlling the time that high-risk food is in the danger zone.

High-risk and low-risk foods

High-risk foods pose a greater food safety risk as they have the right characteristics for bacteria to multiply. Therefore they require careful handling and strict time and temperature control.

High-risk foods have the following characteristics:

  • They are ready-to-eat– because they will not be subject to cooking or reheating if they get contaminated with pathogenic bacteria it will not get killed. Instead the pathogenic bacteria will remain on the food until it is eaten. This is how food poisoning may occur. Examples of ready-to-eat foods include cooked meats and dairy products.
  • They are moist- as we have already learnt, bacteria need moisture in order to be able to grow.
  • They are high in protein– this is because bacteria grow best in foods that are high in protein.

Therefore, high-risk foods require strict time and temperature control.

Food handlers must be trained to take steps to minimize the time that high-risk food items are within the danger zone to prevent food poisoning bacteria from multiplying to unsafe levels.

Low-risk food items are those which can be stored at room temperature and do not need to be kept chilled or frozen. This is because generally, one or more of the things bacteria require to grow would have been removed. Low-risk foods include:

Dried products such as bread, biscuits, dried rice, pasta and cereals

Products that are high in sugar such as chocolate, sweets, jam and preserves

Acidic products such as pickled foods

Unopened canned or tinned foods

Remember, low-risk foods should still be protected from contamination i.e. physical or chemical contaminants.

Cross-contamination and preventing contamination

Preventing cross-contamination is essential to preventing food poisoning. Cross-contamination is when bacteria gets transferred from a contamination source (i.e. raw meat) to a ready-to-eat product.

There are two ways in which cross-contamination can occur:

  1. Direct cross-contamination – the source of the bacteria comes into direct contact with food. An example would be raw meat in a fridge physically touching cooked meat. Or raw meat juices dripping onto a ready-to-eat product (such as a cream cake).
  2. Indirect cross-contamination– this involves a ‘vehicle’. In terms of food safety, a vehicle is something that helps bacteria travel from the source onto the food. For example hands, knives, utensils or chopping boards, cleaning cloths, and door handles, switches, taps, food contact surfaces, equipment, packaging, machinery and sinks.

It is really important that food handlers know how to control cross-contamination. They can take the following steps:

  • Ensure that raw and ready-to-eat foods are separated at all times
  • Use single-use, disposable or colour-coded cloths for cleaning
  • Ensure thorough cleaning and disinfection is in place
  • Use separate sinks for hand washing, for washing food and washing equipment
  • Ensure that all food is covered/packaged adequately when not being prepared
  • Ensure that premises are free from pests at all times
  • Ensure that food handlers maintain high levels of personal hygiene and wash their hands regularly and effectively
  • Food business operators need to ensure that food handlers are adequately trained, instructed and supervised


Unlike bacteria, viruses do not multiply in food. Instead, they use food purely as a way to enter the body and then cause food-borne illness.

What happens is, once the food is ingested, viruses multiply inside the human body.

Fortunately, viruses are killed by thorough cooking. In relation to food safety, the main viruses of concern are Norovirus and Hepatitis E.

Chemical contamination of food

Chemical Contaminant

Chemical contamination in food means the presence of harmful chemicals in foods.

Some forms of chemical contamination may only taint food, meaning only the taste will be affected. Other toxic chemicals in food can (e.g. bleach) be extremely harmful and can cause severe vomiting and burning of the throat. Some chemicals can even cause long-term illnesses such as organ damage or cancer.

There are a number of sources of chemical contamination:

  • Incorrect/ excessive use of pesticides used to treat fruits and vegetables
  • Cleaning chemicals that should not be used in a food room (i.e. bleach)
  • The residue of cleaning chemicals left on worksurfaces and equipment
  • Spraying of cleaning chemicals next to open food
  • Delivery vehicles used to transport chemicals as well as food
  • Chemicals stored next to food items
  • Leaving food in open tins. You may not realise but once opened, acidic tinned foods (i.e. tinned fruit) can react with the metal of the tin and can be absorbed by the food. This is harmful and the food must not be eaten. Once you have opened a tin of food you must transfer the remaining food to a suitable container before placing into the fridge.
  • Food stored in chemical containers. This may sound obvious but as an EHO this is something I have come across. Even if chemical containers have been rinsed out, residue of the chemical could remain. They must not be used to store food in.

Chemical contaminants can be controlled by:

  • Storing cleaning products away from food
  • Never storing food in chemical containers or vice versa
  • Using chemicals in line with the manufacturer’s instructions
  • Ensuring all open food is covered/removed before carrying out cleaning tasks
  • Ensuring any chemicals used in food rooms are food safe. This means they are non-toxic, non-tainting, non-perfumed and non-corrosive.
  • Ensure food and chemicals are delivered separately (use reputable suppliers)
  • Thorough the washing of fruit and vegetables to remove pesticide residue 

Allergenic contamination of food


Allergenic contaminants are naturally occurring proteins in foods that cause abnormal immune system responses in certain people. Extreme care should be taken when dealing with allergens and preparing food for someone with a food allergy.

In terms of the law, there are 14 allergens that food businesses are required to declare. These include the more common ones such as nuts, peanuts, milk and eggs and the unusual ones including lupin, celery, mustard and sulphites.

Food establishments in the retail and catering sectors are required to:

  • Provide allergen information to their customers
  • Handle and manage food allergens effectively in food preparation.

Whilst any food can cause an allergic reaction, by law, food businesses are required to tell their customers if any food they provide contains any of the 14 allergens as these 14 are identified as most commonly causing food allergies.

It is important for food handlers to take steps to avoid cross-contamination when preparing food to protect customers with food allergies. This is because allergic reactions to food can be triggered by only a tiny amount of an allergen.

There are a number of actions that can be taken. These include:

  • Cleaning utensils thoroughly before each use, especially if they were used to prepare foods containing allergens
  • Washing hands thoroughly between preparing dishes with and without certain allergens
  • Storing ingredients and prepared foods separately in closed and labelled containers
  • Keeping ingredients that contain allergens separate from other ingredients
  • Using separate equipment, utensils and preparation areas for foods containing allergens
  • Using separate fryers for cooking certain foods. For example; to provide chips that are gluten-free, you could not use the same oil which has previously been used to cook battered fish

Learn more about allergens here.


The four types of contamination are physical, microbiological, chemical, and allergens.

Food business owners need to ensure that food handlers have adequate food safety training. Control measures to manage the risk of contamination should be set out in a effective food safety management system.

Bacteria require certain conditions for growth. These are time, warmth, moisture and food. Spores and toxins are produced by some bacteria.

Cross-contamination occurs when bacteria are transferred from a contamination source (i.e raw meat) to a ready-to-eat product.

High-risk foods are those which are ready-to-eat, moist and high in protein and as such require strict time and temperature control.

Viruses, unlike bacteria, do not multiply in food. Instead, they use food purely as a means to enter the body and cause foodborne illness.

It is essential that food handlers are aware of the 14 allergens and that allergens are managed effectively in every food business.

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