Humans do have anal glands, but they are nothing like the anal sacs that dogs and cats famously possess. Where your dog has a pair of scent-producing pouches flanking the anus, you have a handful of tiny, mucus-secreting glands buried in the wall of the anal canal. The two structures share a name and a general neighborhood, but their anatomy, function, and day-to-day relevance are worlds apart. The confusion is understandable, since “anal glands” gets tossed around in veterinary contexts so often that people assume every mammal must have the same equipment.
What Human Anal Glands Actually Are
Human anal glands are small, tubular structures tucked inside the lining of the anal canal. They drain into tiny pockets called anal crypts along the inner surface of the anus. A person typically has somewhere between two and eleven of these glands, and most of them sit just beneath the mucosal lining, though some extend into the muscle of the internal sphincter.1PubMed. A Review of the Anatomy of Anal Glands Relevant to Cryptoglandular Fistulas; Are We on the Right Track? They are classified as merocrine glands, meaning they release their secretions without destroying the cell in the process.
What do they secrete? Mucus. Histological studies have found mucus-producing cells in all the anal glands examined, with secretions visible inside the gland lumens. Each gland is also wrapped in a thin layer of myoepithelial cells, muscle-like cells that help squeeze out the mucus.2PubMed. Histoanatomy of anal glands The mucus lubricates the anal canal during bowel movements, which is a helpful but unglamorous job. There is no volatile chemical cocktail, no pheromone signal, no territorial marking. Human anal glands are plumbing accessories, not communication devices.
How Dog and Cat Anal Sacs Differ
The structures people typically mean when they say “anal glands” in a pet context are actually anal sacs, and they are a completely different organ. Dogs and cats each have a pair of these sacs, one on either side of the anus, nestled in the space between the internal and external anal sphincter muscles. Each sac opens to the outside through its own short duct at the edge of the anus.3PubMed Central. Diagnostic imaging features of normal anal sacs in dogs and cats The sacs are lined with squamous epithelium and surrounded by connective tissue packed with both sebaceous and apocrine glands, which together produce the pungent, oily secretion pet owners know all too well.
The gland composition differs between species. In dogs, apocrine glands dominate, producing a more watery secretion. In cats, the sebaceous and apocrine glands are more evenly distributed, which means cat anal sac fluid tends to be more lipid-rich. Cats also have their duct openings positioned slightly more to the side. These differences may help explain why cats deal with anal sac problems less often than dogs do.4PubMed Central. A Cross-Sectional Study on Canine and Feline Anal Sac Disease
The size difference is dramatic. A dog’s anal sac can be roughly the size of a grape or a small marble, depending on the breed. A human anal gland is a microscopic tube. You would need a microscope to see one in tissue; your vet can palpate your dog’s anal sacs through the skin with a gloved finger. These are simply not the same organ operating at different scales. They developed independently and serve entirely different purposes.
Why Pets Have Anal Sacs and You Don’t
The anal sacs of dogs, cats, and most other carnivores exist primarily for chemical communication. The secretions are loaded with volatile organic compounds, including fatty acids, ketones, aldehydes, esters, and alcohols, that carry information about the animal producing them.5PubMed Central. Comparison of volatile compounds of anal sac secretions between the sexes of domestic dog (Canis lupus familiaris) This is what your dog is investigating when it sniffs another dog’s rear end. The chemical profile varies by sex, and researchers have identified sex-specific compounds, such as certain esters found only in female dogs and certain ketone derivatives found only in males.
Much of this chemistry is not produced by the animal’s own cells but by bacteria living inside the anal sacs. In dogs, symbiotic bacteria are thought to generate the palette of small volatile molecules that the animal then broadcasts to others of its species.6PubMed Central. Odorant-binding proteins in canine anal sac glands indicate an evolutionarily conserved role in mammalian chemical communication The same dynamic has been documented in cats, where metagenomic sequencing of anal sac contents reveals a diverse microbial community whose metabolic output correlates with the volatile compounds present in the secretion.7PubMed Central. Characterization of the microbiome and volatile compounds in anal gland secretions from domestic cats (Felis catus) using metagenomics and metabolomics In essence, these animals outsource part of their scent identity to their microbiome.
This is a far cry from what human anal glands do. The mucus your anal glands produce has no demonstrated role in signaling, identity, or social communication. Humans do produce body odors that carry biological information, but the major site for that is the armpit, not the anus. The apocrine glands in the human axilla interact with skin bacteria in a way that researchers have described as analogous to scent glands found in other primates.8PubMed. D’scent of man: a comparative survey of primate chemosignaling in relation to sex But even the human armpit falls short of what a dog’s anal sac accomplishes. No bioassay-guided study has successfully isolated a true human pheromone, so the extent to which human body odor functions as a deliberate signal, rather than just an incidental byproduct of glandular activity, remains an open question.
The Evolutionary Picture
Anal sacs are widespread among carnivores, but they are not universal across mammals. Primates, as a group, moved away from anal-region scent signaling a long time ago. A comparative survey of primate chemosignaling found that all major primate groups, from lemurs to humans, do have scent-producing organs of some kind, but the emphasis shifted over evolutionary time toward other body regions and other sensory channels.8PubMed. D’scent of man: a comparative survey of primate chemosignaling in relation to sex Lemurs, for example, have specialized wrist glands and chest glands that they use to scent-mark. Old World monkeys and apes rely more on visual and auditory signals and less on dedicated scent organs.
Humans sit at the far end of this trend. We lost the vomeronasal organ (the specialized nasal structure many mammals use to detect pheromones) in any functional sense. The anatomical remnant exists, but it lacks the critical neural connections that would let it send chemical signals to the brain the way it does in rodents or snakes. We also lost dedicated anal scent structures. The tiny mucus glands that remain in the human anal canal are not vestigial anal sacs. They are a different lineage of tissue entirely, and they never served a signaling function.
So the honest answer to “why don’t humans have anal sacs?” is that our primate ancestors abandoned that particular communication channel millions of years ago. As vision became the dominant sense and social bonding shifted toward face recognition, vocalizations, and eventually language, the selective pressure to maintain a complex anal scent organ disappeared.
When Human Anal Glands Cause Trouble
Most people go their entire lives without ever knowing they have anal glands, which is exactly how it should be. The glands become clinically relevant only when they get infected. If bacteria invade one of these small glands, the resulting infection can progress to an anorectal abscess, a painful, swollen pocket of pus near the anus. In a substantial number of cases, that abscess eventually forms a tunnel, or fistula, connecting the infected gland to the skin surface.9Journal of the Medical Association of Thailand. Predictive Factors and Timing of Developing Anal Fistula after Drainage of Cryptoglandular Anorectal Abscess
This process, called cryptoglandular infection, is the leading explanation for why most common anal fistulas develop. The gland becomes blocked, bacteria multiply in the trapped secretions, and an abscess forms. Drainage of the abscess provides relief, but a fistula can develop afterward, sometimes requiring surgical treatment. The anatomy of the glands matters here because glands that penetrate deeper into the sphincter muscle tend to produce more complex fistulas that are harder to treat.1PubMed. A Review of the Anatomy of Anal Glands Relevant to Cryptoglandular Fistulas; Are We on the Right Track?
Human anal glands do not become “impacted” the way dog anal sacs do. You will never need to have them manually expressed. The clinical problems are inflammatory and infectious, not mechanical. If you develop pain, swelling, or drainage near the anus, the issue is an abscess or fistula, and the treatment involves a colorectal surgeon, not a groomer.
Common Anal Sac Problems in Dogs
Dogs deal with a very different set of anal-region troubles. The most common issue is impaction, where the secretion inside the anal sac thickens and cannot drain normally through the duct. This leads to the classic “scooting” behavior, where the dog drags its rear end along the floor. Left untreated, impaction can escalate to sacculitis (inflammation of the sac), infection, and eventually abscess formation with potential rupture through the skin.
A retrospective study of dogs treated for anal sacculitis found that the average age at onset was about four and a half years, and interestingly, atopic dermatitis (the canine equivalent of eczema) was the most frequent co-existing condition.10PubMed. Local treatment for canine anal sacculitis: A retrospective study of 33 dogs This suggests that underlying skin inflammation may predispose the sac lining to problems, not just poor diet or insufficient fiber, as is commonly assumed.
One approach to managing recurrent impaction that has gained traction involves dietary supplementation. A trial testing a fiber-and-probiotic oral chew found that dogs receiving the supplement were significantly less likely to need manual expression over a four-month period. In the untreated group, over 60% of dogs required manual expression by the end of the study, compared to about 19% in the supplement group.11PubMed Central. Efficacy of an oral chew containing fibre and Bacillus velezensis C‐3102 in the management of anal sac impaction in dogs The idea is straightforward: firmer stools create more mechanical pressure on the sacs during defecation, helping them empty naturally. Adding beneficial bacteria may also help normalize the microbial environment inside the sacs themselves.
Cats get anal sac problems too, though less frequently. The difference in gland composition and duct position mentioned earlier likely plays a role. When cats do develop impaction or infection, the signs are subtler than in dogs. Cats may lick excessively at the area, strain to defecate, or leave a foul-smelling discharge on surfaces where they sit.
Anal Sac Cancer in Dogs
A more serious condition specific to animal anal sacs is apocrine gland anal sac adenocarcinoma, a malignant tumor arising from the apocrine glands in the sac wall. This cancer is locally aggressive and prone to early spread. At the time of first diagnosis, somewhere between a quarter and more than 80% of affected dogs already have metastases to nearby lymph nodes, and up to roughly a third may have distant spread to other organs.12PubMed Central. Is There Anything New in Canine AGASACA? The cancer usually affects one sac, though bilateral cases occur in a minority of dogs.
A notable feature of this tumor is that it can cause dangerously elevated blood calcium levels, a condition called paraneoplastic hypercalcemia, which shows up in roughly one in six to one in two affected dogs. This sometimes leads to diagnosis: the dog comes in for increased thirst and urination, bloodwork reveals high calcium, and the tumor is discovered on rectal examination.
Treatment typically combines surgery with additional therapy. Dogs treated with surgery plus adjuvant therapy tend to survive considerably longer than those treated with chemotherapy alone. The strongest outcomes have been reported when radiation is included, with median survival times reaching roughly two to two-and-a-half years in some studies.12PubMed Central. Is There Anything New in Canine AGASACA? Key prognostic factors include the size of the primary tumor, whether lymph nodes are already involved, and whether distant spread has occurred.13Journal of Veterinary Internal Medicine. Clinical Stage, Therapy, and Prognosis in Canine Anal Sac Gland Carcinoma
Researchers have recently begun characterizing molecular targets on these tumors, including a receptor called PDGFRβ, which was expressed in the vast majority of tumors examined and was particularly abundant in certain growth patterns. This opens the door to potential targeted therapies, though that work is still early.14PubMed Central. PDGFRβ Expression Across Canine AGASAC Subtypes and Metastases: Morphologic Insights and Possible Therapeutic Implications
Humans do not develop this cancer because they lack the apocrine-gland-lined sac where it originates. The small mucosal glands in the human anal canal can develop their own pathologies, but anal sac adenocarcinoma is exclusively an animal disease. When people develop cancer in the anal region, it is a different type entirely, typically squamous cell carcinoma of the anal canal, which arises from a different cell lineage.
The Butt-Sniffing Question
Understanding the difference between human anal glands and animal anal sacs also clarifies why dogs are so fixated on sniffing each other’s rears. They are reading a chemical dossier. The volatile compounds in anal sac secretions carry information about species, sex, reproductive status, and possibly individual identity, all encoded in the relative proportions of fatty acids, esters, and other molecules.5PubMed Central. Comparison of volatile compounds of anal sac secretions between the sexes of domestic dog (Canis lupus familiaris) The bacteria living in the sacs are central to this process, acting as biochemical factories that convert host-derived substrates into the specific volatile cocktail that other dogs detect and interpret.6PubMed Central. Odorant-binding proteins in canine anal sac glands indicate an evolutionarily conserved role in mammalian chemical communication
When your dog sniffs you in the same region, it is applying the same instinct to anatomy that does not cooperate. You produce no anal sac secretion, no volatile chemical signature from that area. Your dog may still pick up information from skin bacteria, sweat, or other sources, because a dog’s nose can extract meaningful chemical data from almost anything biological. But you are not broadcasting the same structured signal that another dog would be. The hardware for that particular conversation was decommissioned in our evolutionary lineage a very long time ago.