Not facial hair specifically - though it can - but body hair generally and certainly pubic hair. It is a product of evolution. The hair increases perspiration, which increases the release of pheromones and thus increases, in evolutionary terms, your chances of securing a mate. (BO is caused when dirt mixes with perspiration and produces bacteria. It is NOT the same thing as pheromones, which are more easily subconsciously picked up by men and women when the body is relatively dirt free.) Of course, this is all at the margins. As we evolved we began to rely on other things - verbal cues, certain physical characteristics and as civilization evolved, certain cultural influences. You are no longer just an animal, and therefore you are not driven purely by animal instinct, meaning that your involuntary reaction to pheromones is nothing like what it would have been for your prehistoric ancestor, say 50,000 years ago. (Facial hair, in fact, is the least important in terms of your pheromones as over evolution the sweat glands in the human face have atrophied to some extent. One other fun fact, a recent study found that women tended - there is that word again - to view men with facial hair as less trustworthy and therefore less ideal as sex partners. That is to say that cultural perceptions have overtaken sexual instinct in this area.) Now, aren't you glad you asked?