If its a female, get a close female/friend associate to tell her. If its a male coworker, get a close male buddy/associate to tell him. Make sure you tell your supervisor of this possible confrontation.
I'm assuming you are all adults in this working environment. Work and life is a two way street. We all have to live and work in the same environment. The key way to confront this situation is with gentle diplomacy.
Make sure your complaint is an actual complaint against the person's hygiene and not something fueled by a personal dislike or grudge against the individual. Make sure the person you are addressing is aware that this is indeed the fact. Others might be needed to be considered as second opinions on the person's questionable hygiene but don't make it a mob rule where the person in question might become defensive.
The person might be in a depression and anything sounding like a mob rule might make her or him irrationally defensive.