A perianal abscess almost always starts with a blocked gland inside the anal canal. There are small glands lining the inside of the anus, and when one of their ducts gets clogged, bacteria from stool become trapped, triggering an infection that builds into a pocket of pus. The process can take just days to go from a subtle ache to a painful, swollen lump near the anus.
The Glands That Cause the Problem
Most people don’t know these glands exist. Tucked into the lining of the anal canal, roughly at the midpoint between the inside and outside of the anus, sit anywhere from 2 to 11 tiny secretory glands. Each one drains into a small pocket called a crypt. The glands are mostly located just beneath the surface tissue, but some extend deeper, passing through the inner ring of muscle that keeps the anus closed (the internal sphincter).
This anatomy matters because it creates a vulnerability. A gland that passes through the sphincter muscle has a longer, narrower drainage path. If that path gets blocked, bacteria have a warm, enclosed space to multiply. Research suggests that some people are simply born with gland anatomy that makes them more prone to infection, particularly when their glands take a deeper route through the sphincter.
How Infection Develops Step by Step
The most widely accepted explanation, first described by surgeon Alan Parks in 1961, follows a clear sequence. It begins when a gland duct becomes obstructed. The blockage might come from hardened stool, swelling from minor trauma, or inflammation in the surrounding tissue. Once blocked, the gland can no longer drain its normal secretions into the anal canal.
Gut bacteria, which are always present in the anal canal, infiltrate the stagnant gland. They spread along the gland’s channel, typically following a path between the two layers of sphincter muscle. The immune system responds with acute inflammation: white blood cells flood the area, tissue breaks down, and pus accumulates. This collection of pus is the abscess.
Depending on which direction the infection tracks, different types of abscesses form. The most common is a perianal abscess, which pushes toward the skin surface near the anus. Less commonly, the infection can spread outward through the deeper muscle layer and form an abscess higher up or farther from the anus, which tends to be harder to detect and more painful.
What It Feels Like Early On
The first sign is usually a dull, persistent ache near the anus that doesn’t go away. Unlike hemorrhoid pain, which tends to flare during bowel movements and then ease, abscess pain is typically constant and gets worse over days. It can feel dull, sharp, aching, or throbbing.
As the infection grows, the skin around the anus may become red, warm, and firm to the touch. Some people develop fever or chills. Others notice changes in bowel habits, either constipation from avoiding painful movements or loose stools. Within a few days, the area often develops visible swelling with a soft, fluid-filled center beneath taut skin. By this point, sitting, walking, and coughing can all intensify the pain significantly.
Who Gets Perianal Abscesses
Men develop perianal abscesses about 1.8 times more often than women, and the peak age is in the 20s and 30s. The reasons for the male predominance aren’t entirely clear, though differences in gland anatomy and hormonal factors may play a role.
Smoking is one of the strongest modifiable risk factors. A study comparing people with anal abscesses and fistulas to matched controls found that current smokers had roughly 12 times the odds of developing these conditions compared to nonsmokers. The mechanism likely involves smoking’s effects on immune function and tissue healing in the anal canal.
Crohn’s disease carries a particularly high risk. Between 13% and 27% of people with Crohn’s develop perianal disease in population-level studies, and that number climbs to 35% to 45% at specialized treatment centers. When perianal abscesses appear alongside a new Crohn’s diagnosis, the overall disease course tends to be more aggressive, progressing faster to complications that require stronger medications or surgery.
Causes Beyond Blocked Glands
While the blocked-gland mechanism accounts for the majority of perianal abscesses, other conditions can produce similar-looking infections in the same area. Hidradenitis suppurativa, a chronic skin condition where hair follicles become blocked, causes painful lumps in areas where skin rubs together, including the groin, buttocks, and perianal region. These lumps can look and feel like abscesses but stem from a completely different process involving the hair follicles rather than the anal glands. The condition is linked to genetics, hormones, smoking, and excess weight, not to poor hygiene.
Other less common causes include infected skin wounds near the anus, sexually transmitted infections, and complications from prior anal surgery. In people with weakened immune systems, whether from diabetes, HIV, or medications that suppress immunity, ordinary skin bacteria can gain a foothold more easily and progress to abscess formation.
Why Abscesses Can Become a Recurring Problem
A perianal abscess is treated by draining the pus, which usually provides rapid pain relief. But drainage doesn’t always resolve the underlying issue. The original infected gland can leave behind a small tunnel, called a fistula, connecting the inside of the anal canal to the skin surface where the abscess drained.
This is not a rare complication. A large multicenter study tracking patients for about three years after abscess drainage found that 34.5% developed a fistula. Earlier research has reported rates ranging from 26% to 46%. A fistula allows bacteria to continue traveling from the gut to the skin, causing recurring infections, intermittent drainage, or a new abscess forming in the same area. Abscesses and fistulas are really two phases of the same problem: the abscess is the acute infection, and the fistula is the chronic channel it can leave behind.
This is why a single perianal abscess, even after successful drainage, sometimes marks the beginning of a longer treatment course. If the underlying gland or its tract through the sphincter muscle isn’t addressed, the cycle of blockage, infection, and abscess can repeat.