Do you happen to use any lotion?
Would this before or after you shower?
Most likely you produce more salt than your wife. And if you are more active then you probably produce more sweat. Dogs love the taste of salt. Not only that he has found it comforting to him to get his time in with you when you are in bed. Try a different time of day laying in bed and see if he repeats the same behavior. It is either for salt, comfort, or for him to express his like for you.