very sweaty sex

A senior couple goes to the doctor. The doctor first visits the husband:
Everything seems to be fine. Are you having problems?
Well, nothing special but when I make love with my wife, the first time, there are no problems at all.
But, the second time I feel very sweaty and this annoys me.

After having visited the wife, the doctor asks her a question:
To me, everything is ok but your husband says, when you are having sex, that the first time there are no problems while the second time he gets very sweaty.
Do you know the reason for that?
Sure, doctor. The first time is in January. The second is in August.