Asklemmy

I don't think OP is necessarily talking about skid marks. By nature of a dark, warm, and humid environment with more sweat glands than other areas, things like your crotch and armpits will start to smell quicker than something like your elbow, even if you exercise proper hygiene. It's just the nature of how our bodies function.

I change to a new pair of underwear daily, but I might use the same pair of pants multiple days in a row. If you do this while going commando, your pants might start to smell and you'd probably need to change them daily like you do for underwear.

And this is a bit TMI, but for women specifically, around time of ovulation each month (mid cycle) can mean an annoying discharge of mucus. This is totally normal and healthy and doesn't mean there's any degree of infection. It happens when an egg is released. It's easy to deal with if you just need to change your underwear. But now if you have to deal with it getting in your pants it's a bit more of an ordeal.