Dean never had it in him to tell his brother that he wasn't the only freak in the family, the only one with an ability. He didn't even know if he had always had it or if he got blindsided by some curse some day and nobody realized it, but he became aware of his own ability as a child.
Not that it was that useful, he would have preferred something more cooler. In comparison to Sam he was still a lot better off.
Dean sneezed and felt his throat constrict. Great, for that reaction through a closed door there had to be a lot of them there. Sam opened the door and they saw the reason for Dean's allergy attack: the victim had been a crazy cat lad