How do you approach your colleague about his smell?

I've been managing a small team in an IT company in SF and I am wondering how to approach the topic with my colleague of his smell.
Several colleagues have discretely reported his smell to others but no one ever faced him directly. Being his manager, I feel obliged to take the lead on this topic and tell him that he is incommoding others with his smell.
How would you do that with the tact and politeness that a business situation brings?