well being a man myself, normally it is fine, but you are certainly right that it can get to an unpleasant point. I couldn't tell you what condition your husband might have, but I know with myself if I have been sweating excessively for hours it can smell unpleasant, and I know when men are overweight their thighs get big enough to suffocate where the legs meet the hips. This means any sweat can't evaporate, which is necessary. Even if he isn't a heavy sweater, it would still end up being a moist area.

It's not just this sweat that can make it smell bad though, it is the FUNGUS which just loves to live in moist, dark areas. Fungal Infections can smell absolutely disgusting. All humans have some degree of fungus growing on their skin. Those who sweat a lot, the obese, or poor sanitation and live in filthier environments are more prone to develop serious fungal infections. So your husband could be developing a skin fungal infection there, it has the unfortunate name of "crotch rot". I suggest you research it a bit, and in the meantime, convince your man to start using talcum powder and those types of powders in his crotch during the summer to keep dry. Also, if you think it is fungus, either get some antifungal cream from the pharmacy, although I would get it from the Dr., as it's twice the strength.

Hope this helps.