During the process of decomposition, anaerobic bacteria break down the organic matter in a human body in the absence of oxygen. This process produces gases such as methane, carbon dioxide, and hydrogen sulfide. It also results in the formation of various organic acids and compounds, which contribute to the characteristic odor of decaying flesh.

Aerobic decomposition, on the other hand, occurs in the presence of oxygen. It is typically associated with the breakdown of organic matter in environments such as soil or compost.