No matter what, always make sure there's water in all your p-traps to prevent sewer gas from permeating your bathroom. If for some reason you don't have a p-trap make sure you add one under your sink. A second reason you might have a foul smell coming from your bathroom sink is the growth of biofilm in the pipes.
There is no house that at some time or the other has not faced the problem of bad odor in bathroom. Bathroom is a place which has humidity and moisture all the .
You lean closer to the sink, the shower drain and the toilet as you try to identify. The bad news is that any number of things can cause a sewage smell in your .