How do humans contribute to indoor bacteria levels?

Humans contribute to indoor bacteria levels primarily by shedding them from the skin and respiratory system. The human body naturally harbors a wide array of bacteria, some of which are constantly being shed into the environment. This shedding occurs through various means, including skin flakes, hair, saliva, and respiratory droplets.

When individuals breathe, cough, or sneeze, bacteria can become aerosolized and remain suspended in the indoor air, increasing the overall bacterial load. Similarly, skin exfoliation and natural skin oils can lead to the transfer of bacteria to surfaces within indoor environments, further contributing to bacterial levels.

In contrast, while air conditioning can influence indoor air quality and influence microbial growth by managing humidity levels, it does not directly contribute to bacterial levels as shedding does. Frequent cleaning can actually reduce bacteria rather than contribute to it, and outdoor exposure typically introduces a different set of microorganisms rather than increasing indoor bacteria levels. Therefore, the most direct and relevant explanation of human impact on indoor bacteria levels is indeed through shedding from the skin and respiratory system.