Cross-contamination occurs when gluten-free foods come into contact with foods that contain gluten. It can happen during the manufacturing process, for example, if the same equipment is used to make a variety of products. Some food labels include a may contain statement if cross-contamination is likely.
After getting a tattoo, swimming must be avoided until the skin has stopped peeling and all scabs have fallen off. For most people, this means waiting a minimum of two weeks.
In the United States, you must wait 12 months after getting a tattoo or body piercing before donating blood if your state does not regulate tattoo facilities. This is because bloodborne diseases may be spread by needles, and no one has come up with a good way to vet the tattoo and piercing parlors as not re-using needles.