Mold
Mold appears or is produced where moisture, darkness and poor ventilation is present. So, in the case that you do have moisture in any part of your home, make sure that it is dried out soon, that is has good ventilation and that whatever was causing the moisture is fixed.
Like in these pictures you can see that in this first pic on the left there was major mold in the kitchen. The homeowner did not realize that there was a small leak under the sink and did not noticed it. When he finally did there was already mold growth.
The second picture on the right is after SERVPRO of Bellflower went in and removed all the bottom cabinets to where the mold extended. Our team only used SERVPRO professional chemicals to clean, and prevent it from growing again.