Microbiological hazards occur when food becomes contaminated by microorganisms which can be found in the air, food, water, refuse, soil, animals and the human body. Many microorganisms are beneficial and necessary for life itself, however, given the right conditions, some microorganisms may cause a foodborne illness.

Microbiological hazards include microorganisms' such as; bacteria, parasites, fungi and viruses. They can develop in poorly handled food or through contamination from an outside source. it is a fundamental principle of food safety to ensure that produce is purchased from an approved (nominated) supplier.