If it's a bathroom sink , then it's more than likely hair. Nice little tool called a Zip-it that is only a couple of bucks and is the best drain cleaner ever made ! You can get them almost anywhere.
Why does my drain get clogged?
Whether you're dealing with a plumbing emergency or you've just noticed that the water is draining slowly from your tub or sink, calling a drain clearing expert like drain cleaning Camden county NJ is something that you need to do immediately. Drainage problems in bathrooms mostly occur due to hair. It may be either be removed by the tool suggested or you may also call an expert if you think the problem is serious.