One who shows his nega to a kohein might benefit from it, or he might suffer a disadvantage, as follows: if one was confirmed unclean and the signs of his impurity disappeared, and the nega broke out all over him before he could show it to a kohein, he is ritually clean; had he shown it to the kohein, he would have been ritually unclean. If he had a white spot with nothing else in it and it broke out all over him before he could show it to a kohein, he is ritually unclean; had he shown it to the kohein, he would have been ritually clean.
A boil or a burn may be rendered unclean for a week by two signs: white hair or spreading. A boil is an injury that one receives from wood, stone, olive residue, the waters of Tiberias or anything else whose heat is not generated from fire. A burn is caused by a live coal, hot ashes or anything whose heat comes from fire.