Food irradiation is used to prevent the growth of bacteria, insects, viruses in food. Radiation interferes with the ability of the DNA of the organism to replicate. Irradiation may slow sprouting in food. It can be used to delay the onset of ripening of various foods. Microorganisms that cause a food to spoil can no longer carry out their life functions leading to spoilage, thus irradiation can extend the shelf life of meats, fish and poultry. However, radiation can cause subtle changes to the chemicals within the food although the food itself doesn't become radioactive. Although these practices are deemed "safe" since their use in the 1950's, many critics feel that not enough research has been done for a long enough time to be absolutely certain of that.