The human body has three primary lines of defense ... The immune system’s three lines of defense include physical and chemical barriers, non-specific innate responses, and specific adaptive ...

Additionally, It is part of the body's non-specific first line of ... Stomach acid is a chemical barrier against infection.

Stomach acid is a chemical barrier against infection. It is hydrochloric acid and is strong enough to kill any pathogens that have been caught in mucus in the airways or consumed in food or water.