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'''Keratinization''' is the process whereby the surface of the [[glans ]] and remaining [[preputial mucosa| mucosa ]] of the circumcised penis become dry, toughened and hard. Normally, the glans is covered by the [[foreskin]], which moisturizes the area by [[transudation]], keeping the surface of the glans and inner mucosa moist and supple. After circumcision, however, the glans and surrounding mucosa become permanently externalized, and they are exposed to the air and the constant abrasion of clothing. These areas dry out, causing layers of keratin to build, giving the glans and remaining mucosa a dry, leathery appearance.

It was hypothesized in the past that the layers of keratin resulting from circumcision provided a barrier of protection against sexually transmitted diseases. In 1986, [[Aaron J. Fink ]] invented the idea that circumcision could prevent the transmission of HIV, arguing that the hard and toughened glans of the circumcised male resisted infection, while the soft and sensitive foreskin and glans mucosa of the intact male were ports of entry.<ref>Fink, Aaron J. "A possible Explanation for Heterosexual Male Infection with AIDS." ''New England Journal of Medicine'' 315, 18 (1986): 1167</ref>