The immune system guards its host from infection with layered defenses of growing specificity. Actual physical barriers reduce pathogens which include microbes and viruses from moving into the organism.[one] If a pathogen breaches these boundaries, the innate immune system offers an instantaneous, b

natural - present in or made by nature; not synthetic or imitation; "a natural pearl"; "natural fuel"; "natural silk"; "natural blonde hair"; "a natural sweetener"; "natural fertilizers" c. Biology Not made or adjusted artificially; not