Bloom: Also known as plume (both terms are correct), bloom is a naturally occurring phenomenon, a grayish or whitish fuzz that can appear on a well-aged cigar. It is not mold and is completely harmless. Bloom is a residue from the fermenting oils within the cigar and is indicative of proper storage conditions. It first appears on the surface of a cigar as tiny crystals and can eventually make the cigar look dusty. A more advanced bloom gives an opaque white look to the entire cigar.
You can identify bloom when it appears: tiny white or gray spots, evenly spaced on the cigar, that easily brush off when gently wiped with your finger or a soft cloth.
A sign of proper storage conditions, many smokers actually prefer a cigar with bloom. Cigars with advanced plume have a pleasant tobacco aroma…and some say it makes for a richer smoke.
Mold: Mold is a fungus. It can appear on the surface of cigars when the storage conditions exceed proper humidity and temperature levels. Mold looks like blue/gray or black patches or clumps on the surface of the cigar. They do not easily wipe off. Mold spreads by producing spores.
Two other indicators of mold are damp cigars that do not burn well and produce a foul odor.
Mold is not good for cigars, and affected cigars should be promptly removed from the humidor to keep the mold from spreading to your other smokes.