Commensalism is the ecological interaction in which one individual benefit while the other is not benefited neither harmed. Commensalism is a harmonious (positive) ecological interaction, since none of the participants is harmed. Example of commensalism are the numerous bacteria that live in the skin and in the digestive tube of humans without being pathogenic neither beneficial. They are innocuous bacteria living in commensalism with humans.

Symbiosis and Other Interactions - Image Diversity: commensalism