Mold claims can be large and hard to pin down: when did the growth start, and what caused it? So many policies add provisions about microbial matter.

Microbial matter generally means mold, fungi, bacteria and similar matter, and some forms also name viruses. One actual form, for example, defines it as fungi, bacterial or viral matter, including mold, mildew and viruses, whether or not the matter is living. The exact wording varies by policy, and each policy's own definition controls what is excluded.

How the exclusion works: an exclusion takes a loss out of coverage even when the claim would otherwise fall within the insuring agreement. Example: a tenant sues a landlord, saying mold in the apartment caused a respiratory illness. The illness is bodily injury, but if the landlord's liability policy excludes injury arising from mold, the exclusion likely bars coverage. The landlord's lack of intent does not matter, because the exclusion turns on the cause of the harm.

Some insurers offer a buyback endorsement that restores limited microbial matter coverage. Read the declarations and endorsements to see what was bought.