To differentiate one HPV viral type from another involves the detection of different genetic structures. In order to effectively type an HPV virus, there must be less than 90% DNA base-pairing homology in specific regions (usually coding areas) between the two types. In other words, one viral type has more than a 10% difference in its genetic structure compared to a genome of a different HPV virus type.
Of the more than 100 HPV viral types that have been detected, approximately 100 have been fully identified and about 40 types are known to be associated with sexual transmission. Genital HPV types are divided into low-risk HPV and high-risk HPV categories.