Gradual, or progressive, hair dyes are typically used by men to colour grey hair. Some of these gradual rinses contain lead acetate, which is classified as a "probable human carcinogen", based on lab tests on animals. However, a review of lead acetate in hair colouring, concluded that the tiny amount of exposure to the substance was "toxicologically insignificant" and these products can be used safely. Cancer Research UK says links have been investigated between hair dyes and cancers, including bladder cancer, breast cancer, leukaemia and lymphoma. However, there is no clear evidence linking hair dyes with any of these cancers. Be sure to follow the product’s instructions carefully and keep the products away from children.