Why do guys sweat a lot in their sleep?

My boyfriend sleeps over a lot and naps next to me, he sweats so much that I have a routine by making sure the fan is on blast and he has the thinnest blanket. It’s slightly odd and I asked him if he sweats at night in his own bed alone, he told me that he doesn’t. I don’t usually sweat and the only heat I feel at night is from him, I’m not sure if it’s because he’s in bed with me or it’s just a guy thing? He gets hot super fast and the sweat starts almost immediately, takes less than 15 minutes into his sleep. It’s not that important but i’ve been wondering, why does it happen?