Anal bleaching is the process of lightening the color of the skin around the anus

Anus

The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...

. It is done for cosmetic purposes, to make the anus more uniform with the surrounding area.
Some treatments are applied in an office by a technician and others are sold as cream that can be applied in the privacy of one's own home.

Side Effects

Possible effects may include mild itching, stinging, redness and dryness in the area of application. Side effects are more likely when the product contains hydroquinone

Hydroquinone

Hydroquinone, also benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, having the chemical formula C6H42. Its chemical structure, shown in the table at right, has two hydroxyl groups bonded to a benzene ring in a para position. It is a white granular solid...

as an active ingredient. Indirect side effects include lower back aches, anal leakage, and possible damage to the rectum.