Most times when a drain clogs, it is because something was put down there that had no business being there, especially in the case of kitchen sinks and toilets. However, for many drains, including the ones in your bathroom, clogs tend to form as a result of oils and other residues from soaps, shampoos, and the like that build up over time. The best way to avoid clogs is to be conscious of what you are putting down your drains and make sure they are treated regularly.