Mold is a type of fungus that grows indoors or outdoors. Like other living organisms, it needs certain conditions to thrive. To answer the question about what causes mold in homes, it is necessary to understand the conditions that encourage its growth. These conditions must be present; Information can be found here.
These pesky fungi originate from invisible spores that get into the house from outside. The wind can carry these very tiny spores into the home. Once they land on moist surfaces, they begin to grow. See here for information about How to Identify the Various Types of Mold.
Mold doesn’t use photosynthesis. That means it thrives in dark and sheltered places.
Damp and wet areas are the optimum location for the survival and growth of mold.
The purpose of fungi is to decompose organic matter in the ecosystem. They need organic matter (food source) to grow. In the house, this can be almost anything from walls, wood, cotton, dust, etc.
Mold can not grow in cold temperatures. That’s why houses are warm enough for their survival.
A house provides endless possibilities for mold to thrive.
These present themselves as moisture from leaking roofs and pipes, poor ventilation, sheltered spaces like basements, and food materials.