Considering Han was in supended animation for a year when he was frozen in Carbonite so I suspect the wounds from his torture he got from ESB are still there.

In between Tatooine and Endor, Leia sees the wounds and decides to lovingly tend to them. Wash them off, rub some cream, maybe lovingly massage him. Just anything mushy and fluffy of Leia taking care of Han.

++ The cuts turn out to be the most sensitive areas on his body. So every time Leia's fingers run there he moans in pleasure.