These are usually places that are subject to dampness.
Attention is directed first to the cellar, kitchen and bathrooms.
Next, humidity in the home should be reduced generally. Where there is mold growth on hard surfaces it can be killed with fungicides. Keep humidity low by air conditioning or dehumidifiers. Removing the mold always requires removing the carpet. It is almost impossible to dry out the carpet or any pad under it, and the mold antigen will persist.