The trend of bleaching one’s butthole or anal bleaching was introduced by porn actors/actresses as they ought to display their nudity onscreen. In order to create that glossy and shining effect, these actors bleach and wax their whole body. But, being a human there are certain portions which are naturally darker skinned than the rest of your body, particularly the anal region. So, these actors felt that even that part too be of same color as no doubt it is private parts which serve more purpose in porn videos than the actor’s face. So they opted for bleaching that area too.