According to Chazal, Tzoraas was the punishment that was given out to people who said bad things about fellow Jews. For example, Miriam was given Tzoraas after she had spoken Lashon Hora about Moshe (במדבר י"ב:י'). We thus see that Lashon Hora is considered a very serious crime. Chazal have said that a person who speaks Lashon Hora about another person is given the other person's sins. This may seem at first to be unfair. Most people would assume that making a nasty comment about someone else surely is not as bad as physically hurting someone. But this is not true. A person who has been hit or hurt by someone else feels pain, but after a while, the pain goes away. A nasty comment or remark, however, can hurt someone for many years and not go away. Someone who makes a comment for example, that a job applicant looks "untrustworthy" may cost that person a job and decrease his chances of getting another job elsewhere. One reason for this is that nasty comments or nasty words about someone else spread very easily.
The Chofetz Chaim once said that speaking Lashon Hora can be compared to opening a bag of feathers on a windy day. Even if someone were to try hard to gather up all the feathers which have blown away, he would not be able to because they will have been dispersed by the wind. Similarly, it is impossible to repair all the damage done by speaking Lashon Hora. Lashon Hora can destroy in one minute a reputation that took a lifetime to establish. Because of this, we are advised to watch whatever we say about one another, and, at least in the time of the Torah, one was afflicted with Tzoraas for not being sufficiently careful.