The first line of defence is your innate immune system. Level one of this system consists of physical barriers like your skin and the mucosal lining in your respiratory tract. The tears, sweat, saliva and mucous produced by the skin and mucosal lining are part of that physical barrier, too.
At the bottom of the follicle is the papilla (pronounced: puh-PILL-uh), where the actual hair growth happens. The papilla contains an artery that nourishes the root of the hair. As cells multiply and make keratin to harden the structure, they're pushed up the follicle and through the skin's surface as a shaft of hair.
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