The introduction of pop-top or easy-open ends to metal cans has increased the convenience of using metal packages because the consumer no longer needs a can opener. Disadavntages of metal include corrosion and reactivity wit food (tin will react with acids in foods).
The can tops are lined with chemicals called bisphenol-A (BPA) and bisphenol F (BPF). US and Japanese scientific studies caused a scare over BPA in 2005. The US study found low doses of BPA could harm the development of young brains. Another US study found that BPA increased breast cancer cell growth. The US studies were done on rats.
Human exposure to BPA from can coatings has been considered minimal and posing no known health risk until January 2007 when the European Union's food agency set a maximum limit for human daily intakes of bisphenol A (BPA), a chemical implicated as a potential carcinogen and widely used in plastic food packaging and cans. This maximum limit is the basis for scientific risk assessments on whether BPA can be used, reduced or banned.
Lining of pop-top cat-food cans has been linked as a possible contributing factor to the epidemic of feline hyperthyroidism (Epidemiologic study of relationships between consumption of commercial canned food and risk of hyperthyroidism in cats by Charlotte H. Edinboro, DVM, PhDJ). The reasearch suggests that overall consumption of pop-top canned (compared to dry) food at various times throughout a cat's life has been associated with greater risk of developing hyperthyroidism. In female cats, increased risk was associated with consumption of food packaged in pop-top cans or in combinations of pop-top and non-pop-top cans. In male cats, increased risk was associated with consumption of food packaged in pop-top cans and age. These findings suggest that the increasing prevalence of feline hyperthyroidism is not only the result of aging of the cat population and that canned foods may play a role.