The inside of canned foods are pretty clean. Proper processing and hygiene ensures that they are free form any contaminants. They are safe to consume as long as within the declared shelf life or no signs of spoilage is observed.
If you’re thirsty and drink soft drinks in can, your mouth comes in direct contact with the can. When you are opening a canned tuna, can opener blade contacts with the can’s surface and with the tuna.
Outside surface of cans are exposed to environmental impurities during transport and storage. Contamination may also occur in groceries and home. Rodents may drop their wee-wee on can’s surface. Insecticides and other spoiled foods could also be a source of dangerous substances.
What do you think could happen if you forgot to wash can before consuming it? I heard from local news that some persons suffered form leptospirosis by consuming canned foods.
According to Wikipedia leptospirosis (also known as Weil’s disease, Weil’s syndrome, canicola fever, canefield fever, nanukayami fever, 7-day fever, Rat Catcher’s Yellows, Fort Bragg fever, and Pretibial fever is a bacterial zoonotic disease caused by spirochaetes of the genus Leptospira that affects humans and a wide range of animals, including mammals, birds, amphibians, and reptiles. The disease was first described by Adolf Weil in 1886 when he reported an “acute infectious disease with enlargement of spleen, jaundice and nephritis”. Leptospira was first observed in 1907 from a post mortem renal tissue slice. In 1908, Inada and Ito first identified it as the causative organism and in 1916 noted its presence in rats.
Humans become infected through contact with water, food, or soil containing urine from these infected animals. This may happen by swallowing contaminated food or water, or through skin contact. The disease is not known to be spread from person to person and cases of bacterial dissemination in convalescence are extremely rare in humans. Leptospirosis is common among water-sport enthusiasts in specific areas as prolonged immersion in water is known to promote the entry of the bacteria. Surfers and whitewater paddlers are at especially high risk in areas that have been shown to contain the bacteria, and can contract the disease by swallowing contaminated water, splashing contaminated water into their eyes or nose, or exposing open wounds to infected water. Occupations at risk include veterinarians, slaughterhouse workers, farmers, sewer workers, and people working on derelict buildings, rowers are also sometimes known to contact the disease.