Any substance that is resistant to putrefaction and decomposition and is capable of penetrating skin is a potential cause of cutaneous foreign-body reaction. Hair is such a substance. The purpose of this article is to focus attention on the fact that extraneous hair, which has become separated from its host, may penetrate skin and act as a foreign body.
In 1880 Hodges1 read a paper before the Boston Society for Medical Improvement in which he originally described sacral pilonidal sinuses. It was his contention that these sinuses result from extraneous hairs entering the integument in a congenital dimple near the coccyx. During the past 15 years a few articles have been published on sinuses developing in the intradigital webs of barber's hands as a result of hair penetration. The literature is otherwise nearly devoid of articles mentioning the ability of extraneous hairs to pierce skin.
SCOTT MJ. Cutaneous Reactions to Embedded Extraneous Hair. AMA Arch Derm. 1957;76(1):39–42. doi:10.1001/archderm.1957.01550190041009