What Causes Cuts And Red Marks On Penis After Intercourse?

often after sex my boyfriend has red marks on the head and shaft of his penis and red lines like cuts, they look very sore. during sex when he has these marks afterwards i feel a burning sensation and am left sore also. its as if we're having an allergic reaction to each other. is this possible? no other contact between us has this effect. my boyfriend has also been to the doctors and, because it is quick to fade the doctor couldnt diagnose. please help.