A hair "follicle," is a small cavity, or sheath of cells, that anchors each hair into the skin. Researchers have found that toxins, drugs, etc., may be absorbed into the body, through not only the skin of the scalp, but also through these hair follicles. This means people should be even more careful what type of chemicals they place upon their heads. Shampoos, dyes, hair products, etc., are often filled with endocrine disrupting, or cancer-promoting agents.
Notice some studies:
“Vaccines May Soon Have Punch But No Ouch…Vaccinations may one day be simply a matter of a quick shower - or maybe just a shampoo. Scientists at Stanford University have found that a simple solution of DNA and water applied to the skin of mice can induce an immune response against the hepatitis B virus. The response is comparable to that from traditional injection into the muscle, the research shows…The DNA vaccine was apparently taken up through the hair follicles of the mice; the mice without hair (what scientists call nude mice) did not show the same reaction…It induced an immune response comparable to that of muscular injection of commercially available hepatitis B vaccine, the researchers said…”
(New York Times, Sept. 7, 1999)
“The role of hair follicles in the percutaneous absorption of caffeine…Every single hair follicle within a delimited area of skin was blocked with a microdrop of a special varnish-wax-mixture in vivo. Caffeine in solution was topically applied…Caffeine…was detected in blood samples, 5 min after topical application, when the follicles remained open. When the follicles were blocked, caffeine was detectable after 20 min…Our findings demonstrate that hair follicles are considerable weak spots in our protective sheath against certain hydrophilic drugs and may allow a fast delivery of topically applied substances…”
(Br J Clin Pharmacol. 2008)