@Benjamin243 it is a real dilemma, because there are two very reasonable priorities in direct conflict with each other.
One priority is to be nice to people who were nice guests.
Another priority is to let hosts know that dealing with the body odor was an issue.
Did these guests have any other reviews?
I know as a host I would want to know about the issue. But you are correct: there is no nice way to say it.
If it were me, I think I would mention it in the nicest way possible, but know that it is still not going to come off as nice. My reasoning is this: my loyalty to the other hosts on AirBnB is a higher priority than my need to be seen as nice. The review system doesn't work if we don't leave accurate reviews, and I count on the previous hosts to warn me if there is a potential issue.
But I don't think anyone would has the right to criticize you for what you eventually decide to do. Both mentioning it and not mentioning it can be well defended as a choice.