My colleague has unfortunate personal hygiene
Because they stink!
Why is it risky?
Even with a friend, it's one of the things we would like to never like to say (let alone hear), and with a colleague ... On the one hand, your well-being at work is involved but then you are delving into extremely personal areas, you could deeply hurt and offend someone.
How do you do it?
Avoid at all costs questionable schemes and subliminal messages like deodorant put in the drawer, moving farther away, or open windows in – 10° weather...
Instead, plan a face-to-face with him. In a moment of calm outside the office and others (coffee break, lunch ...), you can use a formula like: "It's hard for me to tell you about it but I think that you would benefit your relationship at work and elsewhere, I think you're anxious and at times of stress, you tend to sweat excessively ... ".
Hopefully you will have to say no more.