A pilonidal sinus is a sinus tract that often contains hairs. It typically occurs under the skin between the buttocks (the natal cleft), a short distance above the anus. The sinus tract runs vertically in this area. Rarely, it may occur elsewhere on the body.

The exact cause is unclear, though several theories exist. One suggests a minor congenital skin abnormality may lead to the condition, explaining why it sometimes runs in families. Hairs may grow inward rather than outward, contributing to the problem.

Another theory proposes that skin dimples or pits form due to pressure or friction damaging hair follicles. Hair growing in the natal cleft can be pushed into these skin pits, forming the sinus tract.

When a tubular organ or blood vessel becomes excessively narrow, it is a condition referred to as stenosis. Anal stenosis, also known as an anal stricture, is the narrowing of the anal canal, located just before the anal sphincter.

The anal sphincter is a complex part of the body that maintains a seal that can be opened to discharge body waste. It is strong enough to restrict fecal material but sensitive enough to differentiate between solid, liquid, and gas. There are actually two anal sphincter muscles: the internal and the external.

The internal anal sphincter is a thin, white muscle wrapped around the anal canal. It contracts during rest and sleep to prevent leaks. It is an involuntary smooth muscle, similar to intestinal muscles, and cannot be consciously controlled.

An anal fissure is a tear in the lining of the lower rectum (anal canal) that causes pain during bowel movements. Anal fissures generally don't lead to serious problems.

Most fissures heal with home treatment in a few days or weeks (acute fissures). If it persists beyond 8–12 weeks, it is considered chronic and may require medical attention.

Anal fissures are common across all age groups, especially among young, healthy individuals.

Condyloma acuminatum is caused by human papilloma virus (HPV) infection. HPV includes a family of highly infectious, primarily sexually transmitted, double-stranded DNA viruses. The incubation period ranges from three weeks to eight months. Most infections are transient and clear within two years.

Wart-like growths appear around the anus, vulva, or glans penis. There are three main types of condyloma, all sexually transmitted: condyloma acuminatum (warts around the vulva), condyloma latum (a form of secondary syphilis), and condyloma subcutaneum (also known as molluscum contagiosum).