It can be, and for some people in your house more than others. Black mold exposure is linked to coughing, wheezing, headaches, irritated eyes and skin, and flared-up asthma and allergies. Young children, elderly family members, and anyone with respiratory or immune conditions carry the most risk. You do not have to see it to be exposed. Spores are airborne, which is why a persistent musty smell counts as a warning on its own.
The practical danger is just as real: mold means a moisture problem, and both keep growing until the source is fixed. Disturbing a colony without containment, scrubbing it, cutting into the drywall, sends spores through the rest of the house. If you have found black mold, or you suspect it, have it assessed before anyone touches it. Nonstop Restoration inspects for free and remediates with containment, negative air, and HEPA filtration to IICRC standards: (403) 620-8489.