The affliction of tzara'at comes primarily as a result of loshon hara - talking badly about others. The Sages make an amazing statement in the Talmud. They say that to speak negatively about another person is worse than murder. I think everyone would agree that it is terrible to speak negatively about another person. But can it possibly be worse than killing a person? I, for one, would much rather that someone spoke negatively about me than killed me.
In order to understand, we must think a little more deeply about what the Sages are saying. They do not mean that loshon hara is worse than murder in a general sense. Obviously, murder is worse, as proven by the fact that one is obligated to die rather than commit murder, which is not the case with loshon hara. What the Sages mean is that a specific evil is inherent within the transgression of loshon hara, that does not exist within murder. What is it?
Generally when a person kills another, there is a motive - jealousy, money, power, passion. There is a tangible benefit to the murderer and that is why s/he does it. Obviously, that doesn't make it right. It is evil, but in some sense an explainable evil. Were the murderer to be able to achieve the same result without killing, he would probably do so. Of course there are insane psychopaths who kill for fun, but for the most part people who kill would prefer another way. That makes it no less evil, just more understandable.
When someone speaks badly of someone else, however, generally there is no motive, no reason and no tangible gain. It benefits you in no way. You enjoy the evil itself; the negativity, the cruelness and the sense of power that it brings. You also enjoy other people listening to (and enjoying) your evil; it takes two to tango. As such, not only do you enjoy the evil, you drag others down with you.
And one final difference: The one who murders will not learn to enjoy murder and want to do it again. But the one who speaks loshon hara will do so again and again and again. The more you do it, the more it becomes a part of you. While the results of murder may be worse for the victim, the long-term results of negative speech are much worse for the one who speaks it. The shock of having murdered might spur you to change. Speaking loshon hara, on the other hand, will just drag you further and further into the quagmire of petty mediocrity. Not only do you hurt another human being, you destroy your own soul in the process.