Do you tell the candidate that he/she needs a shower, or tell him/her something else?
I have actually had this one happen to me, John, when I was working for an agency. It is amazing the things that come up isn't it? I probably didn't do the right thing, but a couple of us talked to him about all the good things he has done and how they liked him. Then we handed him a stick of deodorant and gave him a toothbrush and toothpaste. I think he got the picture.
I think anyone in this situation needs to tread carefully. There are some cultures where food can really factor into this situation. High intake of strong spices can cause the body to excrete a smell that isn't pleasant. (Garlic comes to my mind immediately.)
I have also been called to a client in the past to address this situation. I had to have a one-on-one conversation with the employee and let them know that there were some complaints about an unpleasant odor on a regular basis. His feelings were really hurt and I felt bad for him but asked him to take corrective action, whether it be more hygienic habits or toning down the spicy food.
It is also not appropriate behavior for coworkers to leave personal care products or air fresheners on the coworkers desk. That can be seen as harassment or bullying.