As a home inspection company in Ohio, we come across mold often. Some people will state that it can not be claimed to be mold unless it is tested, however when it is fuzzy, looks like and smells like mold, it is very very likely mold. We can test it if desired and to verify what it is if someone wants us to.
When we see the mold like substance often we will then get questioned about cleaning it up and killing the mold by using bleach. Bleach is not an EPA registered item for killing mold. Good stuff for non porous surfaces but not good for porous surfaces like drywall, wood, trim, carpet, roof trusses, roof sheathing, etc
Bleach can not penetrate porous surfaces, only the water in the bleach will penetrate, thus “watering” the hyphae (basically the root system of the mold) helping it to grow. The bleach makes it look clean because it removed the color on the surface.
The use of bleach is not the best thing to use for carpets, floor finishes due to corroding the finishes or altering the color in undesirable ways.
If someone tells you to use bleach to kill mold then you know they are misinformed. Also be certain that any solution to a mold problem has to include humidity and moisture control, without controlling moisture in a home mold growth can return and grow again. Poor mold and moisture levels are Indoor Air Quality (IAQ) issues.