Another area involving loshon hara is that of past history. It is forbidden to relate something about an individual’s past which either the speaker or the listener considers shameful, though in reality it is not shameful at all.
Our Sages teach that “at the place where baalei teshuvah (returnees to the path of Torah) stand, perfect tzaddikim (those who have always been righteous) cannot stand” (Berachos 34b). Thus, there is nothing shameful about being a baal teshuvah. Nevertheless, it is forbidden to relate that someone is a baal teshuvah if either the speaker or the listener looks down at such people.
Sefer Chofetz Chaim, 8 Tishrei, page 64