Please use Adobe Acrobat Reader to read this book chapter for free. Just open this same document with Adobe Reader. If you do not have it, you can download it here. You can freely access the chapter at the Web Viewer here. inhibitors. This may explain the huge variation in HPV detection rate: 22 to 60% or 0 to 81.1%, depending on the methods and on the studied population [15]. Recent meta-analysis has demonstrated that HPV is an isolated risk factor for the development of oral carcinoma [2]. Oral squamous cell carcinoma is known to be linked with both heavy drinking and smoking and it has been related to HPV [6, 7]. 3.1. Oral human papillomavirus infection When oral mucosa is considered normal, the epithelium may serve as a container of HPV which would be activated at some point in time and induce injury [16]. A huge number of different oral diseases may be associated with oral HPV, but they rarely cause lesions [17]. Lesions may range from benign warts, which are far more common, to malignant injuries [6]. 3.2. Sexual and nonsexual transmission Many studies have discussed HPV transmission, but the mechanisms involved remain unknown. Unprotected sexual intercourse is its leading cause, particularly oral-genital sex, when the genital mucosa is infected by the virus, which will be present both clinically and subclinically [1, 16] in adolescent and adults. Early sexual relationships, high number of sexual partners, parity, smoking and another sexually transmitted infection may elevate the rate of virus infection [6, 18, 19]. Oral HPV can be transmitted by direct skin-skin contact [3] and self-inoculation [1, 4]. Upper airway transmission has not yet been established [8]. Infant HPV is mainly transmitted at birth by infection of the maternal cervix. Thus, the recurrent laryngeal papillomatosis seems to be acquired by such manner [19, 20]. However, another transmission route is mother-fetus, before, during or after the childbirth [1, 4, 8] that may be made possible by infected amniotic fluid and umbilical cord blood [21]. The transmission of HPV through fomites may also occur [22]. 4. Risk and protective factors In the social sphere, people who have yet to initiate sex life have a low probability of HPV infection. On the other hand, people who started their sex life earlier or have a promiscuous sexual life are more likely to have sexually transmitted infections, including HPV. In the economical sphere, it has been found that low levels of HPV infection were strongly related with higher income levels [4]. Early age initial sexual activity, oral sex, more than one sexual partner, not wearing condoms, infrequent use of condoms all pose important risks to any sexually transmitted infection, such as HPV. Homosexuals tend to have greater number of sexual partners than heterosexuals, and as such, they should be more commonly infected than heterosexuals, but studies have yet to confirm this trend [4, 8]. Oral HPV Related Diseases: A Review and an Update 19 Please use Adobe Acrobat Reader to read this book chapter for free. J...