Biting is a common problem with babies of this age. Think about what is happening: new teeth are coming in, and those little gums hurt. The first thing to do is to make certain he has something to chew on. There are gum teasers (“teething easers”) that work quite well: you cool one briefly in the refrigerator, then give to the baby.
But gum soreness is often only part of the problem. As babies get older, they will often bite anything in reach when they are frustrated—their own arm or hand, somebody else's arm or hand, a nipple, a doll. This is especially worrisome when they are in child care, as nothing upsets a mother more than having her child bitten by another.
The best way to handle it is to prevent it if at all possible; an alert adult can almost always tell when it is going to happen. If you see the signs (tense facial expression, waving of arms), try to distract the baby before the upset escalates to a bite. Offer a toy or a cracker, then pick him up briefly and walk around the room a minute. If you are too late and the bite has already occurred, pick him up and carry him to his bed and say firmly, “Stay there until you calm down.” Don't bite him back; in the long run it will only make things worse.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.