What is the main cause of roaches?

The main cause of cockroaches in homes is a combination of food availability, moisture, shelter, and entry points that provide ideal conditions for German cockroaches and American cockroaches to survive and reproduce, with sanitation and structural factors being primary drivers rather than dirtiness alone. Food is major cause, roaches are attracted to crumbs, grease, food residues on countertops and floors, unsealed food in pantry, pet food left out, and trash, even tiny crumbs invisible to humans can feed many roaches, with German cockroaches needing only small amounts. Moisture is equally important, roaches need water and thrive in humid areas, so leaky pipes, dripping faucets, condensation, wet sponges, and standing water under sinks cause infestations, with American cockroaches often living in drains and basements. Shelter in form of dark, warm, secluded cracks and clutter provides hiding spots during day, including cardboard boxes, paper bags, and piles of clutter where roaches hide and breed. Entry points allow roaches to invade from outdoors or neighboring units through gaps as small as 1/16 inch around windows, doors, pipes, and foundations, through drains, sewer lines, and by hitchhiking in grocery bags, used appliances, and luggage. Seasonal changes also cause roaches, with warm weather increasing activity and rain driving them indoors. While poor sanitation makes infestations worse, even clean homes can have roaches due to moisture and entry points, so main cause is combination of accessible food, water, shelter, and openings rather than just dirt.