Spectacular question, friend! There are two kinds of chocolate bloom:
If the chocolate has a grainy, rough texture and white appearance, it is probably sugar bloom. This happens when chocolate is exposed to moisture -- either stored in a humid environment OR transferred from cold storage to room temperature, which can cause condensation. In both cases, moisture dissolves some of the sugar on the chocolate's surface. When the moisture evaporates, the sugar re-solidifies and leaves behind the grainy, white texture or 'bloom'.
If there is a grayish film appearance on the chocolate, it is probably fat bloom. This happens when chocolate is stored (or transported) at too high a temperature. The high temperature causes the cocoa butter (fat) to soften and make its way to the surface of the chocolate.
Sometimes, fat bloom is also caused by other ingredients in the chocolate. For example, oil in the natural peanut butter filling of my beloved Peanut Butter chocolate bars and bites can sometimes make its way to the chocolate surface and cause bloom.
In all three cases: looks whitish, still safe to eat, still delish.
If you're looking for more facts about bloom, or you're just a food science enthusiast, here are some articles you might enjoy:
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