Why Does My Dog Lick Assholes? The Canine Science Behind
Why does your dog lick asses? Explore the canine science, evolutionary roots, and health implications of this common but misunderstood behavior.
If you share your life with a dog, you have almost certainly witnessed this: your dog approaches another dog (or a human) and goes straight for the rear end with an enthusiastic lick. It is awkward, it is gross, and it is completely normal canine behavior. Here is the direct answer to the question burning in your mind:
While the behavior is rooted in normal canine communication, excessive or compulsive anal licking can sometimes signal medical or behavioral issues that warrant attention. In this deep dive, we will unpack the science, the evolutionary history, and what you as an owner should actually do about it.
The Science of Canine Anal Gland Communication
To understand why a dog licks another dog's (or a human's) rear end, you need to understand the canine anal gland system. Dogs possess two small sacs located at roughly the 4 and 8 o'clock positions around the anus. These glands produce a pungent, oily secretion loaded with volatile fatty acids, trimethylamines, and other organic compounds that are unique to each individual dog.
How the Vomeronasal Organ Processes Anal Scent
When a dog licks or sniffs the anal region, chemical molecules travel to the vomeronasal organ (also called Jacobson's organ), located in the roof of the mouth behind the upper incisors. This organ is connected directly to the accessory olfactory bulb in the brain, which processes social and reproductive chemical signals separately from the main olfactory system.
Research published in Applied Animal Behaviour Science has demonstrated that dogs can distinguish individual identity, sex, and even emotional state through these chemical signatures. The vomeronasal organ is so sensitive that it can detect compounds at concentrations as low as parts per trillion — far beyond human olfactory capability.
The specific compounds in anal gland secretions include:
- Propionic acid and isovaleric acid — short-chain fatty acids that vary between individual dogs
- Trimethylamine — contributes to the characteristic fishy odor
- Indole and skatole — bacterial metabolites that vary with gut microbiome composition
- Steroid derivatives — including androstenone and other hormones that signal reproductive status
According to the Merck Veterinary Manual, anal sac secretions are normally expressed during defecation, but dogs also voluntarily express small amounts during social encounters. When your dog licks this area, they are essentially sampling a complex chemical cocktail that tells them a remarkable amount about the other animal.
Evolutionary Roots: What Wolves Taught Dogs
The Wolf Ancestry of Anal Investigation
Gray wolves (Canis lupus) rely heavily on scent-based social communication. In wolf packs, greeting rituals almost always involve mutual sniffing of the inguinal (groin) and anal regions. This behavior serves multiple evolutionary functions:
- Pack recognition — confirming group membership through shared scent profiles
- Social hierarchy assessment — subordinate wolves present their rear as a deference signal, while dominant wolves initiate investigation
- Reproductive monitoring — detecting estrus status in females through hormonal shifts in anal and vaginal secretions
- Health assessment — sick or stressed pack members produce altered chemical signatures that other wolves can detect
Domestication has modified but not eliminated these behaviors. A 2021 study in Scientific Reports found that domestic dogs retain the same vomeronasal receptor genes as wolves, with only minor variations. The hardware for chemical communication is still fully intact — dogs simply apply it in a domestic context.
When your dog licks another dog's rear end at the dog park, they are performing a behavior that has been refined over millions of years of canid evolution. It is not random, and it is not misbehaving. It is an ancient information-gathering ritual playing out on a suburban sidewalk.
Is It Normal When My Dog Licks Another Dog's Rear?
Yes — in the vast majority of cases, anal licking and sniffing between dogs is entirely normal social behavior. However, context matters. Here is a breakdown of what different scenarios typically mean:
| Scenario | What It Likely Means | Action Needed |
|---|---|---|
| Dog briefly sniffs/licks another dog's rear during greeting | Normal social investigation — gathering identity and status information | None; allow the interaction (3-5 seconds is typical) |
| Dog persistently licks another dog's anal area | May indicate the other dog has expressed anal glands (attracting attention) or your dog is overstimulated | Redirect after 10-15 seconds; check other dog for anal gland issues |
| Dog licks own anal area frequently | Could signal anal gland impaction, allergies, parasites, or skin irritation | Consult your veterinarian if behavior persists beyond 24-48 hours |
| Dog licks human's rear/buttocks area | Seeking scent information; attracted to apocrine sweat glands concentrated in the groin | Redirect with a toy or command; not harmful but socially inappropriate |
| Dog obsessively licks anal area of another household dog | May indicate anxiety, compulsive behavior, or the target dog has a medical issue | Veterinary exam for both dogs; behavioral consultation if medical causes ruled out |
Common Misconceptions About Anal Licking
Because this behavior is embarrassing to humans, a lot of folklore has grown up around it. Let us separate fact from fiction:
| Myth | Fact |
|---|---|
| "My dog is trying to dominate the other dog by licking their rear" | Dominance theory in dogs has been largely debunked by modern behavioral science. Anal investigation is information-seeking, not a power move. Both dominant and subordinate dogs engage in it. |
| "Dogs lick asses because they like the taste" | While some dogs may find the salty, fatty secretions palatable, the primary driver is olfactory information gathering via the vomeronasal organ, not gustatory pleasure. |
| "If my dog licks my private area, they are being sexual" | Dogs do not sexualize human anatomy the way humans do. They are attracted to the high concentration of apocrine sweat glands in the human groin, which produce scent compounds analogous to canine pheromones. |
| "Only male dogs do this" | Both male and female dogs investigate anal regions. Intact males may show more interest in females in estrus, but the base behavior is universal across sexes and neuter status. |
| "I should punish my dog for doing this" | Punishing a natural communication behavior creates confusion and anxiety. Redirecting is more effective and aligns with force-free, positive reinforcement training principles. |
When Anal Licking Signals a Problem
While most anal licking is benign, there are situations where it crosses into a medical or behavioral red flag. Pay close attention to these scenarios:
Your Dog Is Licking Their OWN Anal Area Excessively
If your dog is repeatedly licking, biting, or scooting their own rear end, this is rarely normal social behavior and frequently indicates a medical issue:
- Anal gland impaction or infection — The most common cause. Impacted glands are painful and can lead to abscesses if untreated. Veterinary expression costs $25-$75 per visit; abscess treatment can run $200-$500.
- Intestinal parasites — Tapeworms (Dipylidium caninum) cause perianal itching. Look for rice-like segments near the anus. Deworming treatment costs $15-$50.
- Allergies — Environmental or food allergies can cause perianal dermatitis. Atopic dermatitis affects an estimated 10-15% of dogs (AKC).
- Perianal fistulas — More common in German Shepherds, these painful inflammatory lesions require veterinary treatment and can cost $500-$3,000 to manage.
- Perianal tumors — Hepatoid gland adenomas are common in intact male dogs. Most are benign but require veterinary diagnosis.
- Excessive anal licking lasting more than 1-2 days
- Scooting or dragging their rear on the ground
- Swelling, redness, or discharge near the anus
- Foul odor beyond normal anal gland smell
- Blood in stool or on fur around the anus
- Signs of pain when defecating or sitting
- Lethargy, decreased appetite, or fever alongside anal licking
Your Dog Is Obsessively Licking Another Dog's Rear
Compulsive licking of another dog's anal area — defined as persistent, repetitive behavior that is difficult to interrupt — can indicate:
- The target dog has a medical issue — Your dog may be detecting infection, inflammation, or abnormal secretions before you notice anything wrong. This is actually a useful early warning system.
- Anxiety or stress — Compulsive licking in dogs can be a displacement behavior, similar to nail-biting in humans. A 2022 study in the Journal of Veterinary Behavior found that repetitive licking behaviors correlated with elevated cortisol levels in some dogs.
- Lack of environmental enrichment — Dogs without sufficient mental stimulation may fixate on available sensory activities, including excessive grooming of other dogs.
Breed Variations in Scent-Driven Behavior
While all dogs possess functional vomeronasal organs and anal glands, breed genetics influence how intensely a dog pursues scent-based investigation:
| Breed Category | Examples | Scent Investigation Tendency | Notes |
|---|---|---|---|
| Scent hounds | Beagles, Bloodhounds, Basset Hounds, Coonhounds | Very high | Bred for olfactory tracking; more likely to engage in prolonged sniffing and licking of scent-rich areas. Bloodhounds have approximately 300 million olfactory receptors (vs. ~6 million in humans). |
| Working/herding breeds | German Shepherds, Border Collies, Belgian Malinois | High | Alert and investigative; likely to use scent to assess new dogs and people quickly. |
| Brachycephalic breeds | Pugs, Bulldogs, Shih Tzus | Moderate | Reduced olfactory surface area due to shortened skulls; may rely more on visual cues but still engage in anal investigation. |
| Sighthounds | Greyhounds, Whippets, Salukis | Low to moderate | Primarily visual hunters with less-developed olfactory processing; may show less interest in prolonged scent investigation. |
| Toy breeds | Chihuahuas, Yorkshire Terriers, Pomeranians | Variable | Individual variation is high; some are intensely scent-driven despite small size. |
Understanding your dog's breed tendencies helps set realistic expectations. A Beagle at a dog park is almost certainly going to spend more time investigating rear ends than a Greyhound will — and neither is "misbehaving."
How Is This Different From Humans?
Humans have a vestigial vomeronasal organ that is largely non-functional. We lack the accessory olfactory bulb connections that allow dogs to process pheromones as discrete information channels. Where a dog detects a detailed chemical biography from an anal gland secretion, humans smell... something unpleasant.
Additionally, humans have far fewer olfactory receptor genes — roughly 400 functional genes compared to approximately 800-1,200 in dogs (varying by breed). This means dogs literally perceive a different sensory reality. What we dismiss as "gross" is, to a dog, an information-rich data stream.
Humans also produce apocrine sweat glands concentrated in the axillary (armpit) and inguinal (groin) regions. These glands produce secretions containing steroids, fatty acids, and sulfur compounds — remarkably similar in composition to canine anal gland secretions. This is why dogs are often drawn to sniff or lick human armpits and groin areas. They are not being inappropriate by canine standards; they are investigating the closest human equivalent to an anal gland introduction.
Practical Takeaways for Dog Owners
What to Do (and Not Do) About Anal Licking
- Allow brief greetings — When two dogs meet and spend 3-5 seconds sniffing each other's rear ends, let it happen. This is how they establish identity and assess each other. Interrupting it is like pulling your phone away mid-handshake.
- Redirect prolonged licking — If your dog fixates on another dog's rear for more than 10-15 seconds, use a cheerful verbal cue ("Let's go!") and redirect to a toy or treat. Never yank the leash or scold.
- Train a "leave it" cue — A reliable "leave it" command (trained with positive reinforcement and high-value treats like freeze-dried liver or chicken) gives you a polite way to redirect without confrontation. Expect 4-6 weeks of consistent daily practice (5-10 minute sessions) for reliable performance.
- Check your dog's anal glands — If your dog is licking their own rear, have your veterinarian check for impaction. Small breeds (under 25 lb / 11 kg) are more prone to anal gland issues because they often lack sufficient dietary fiber and stool bulk to express glands naturally during defecation. Adding 1-2 teaspoons of canned pumpkin (plain, not pie filling) per 10 lb of body weight to meals can help promote natural expression.
- Do not punish the behavior — Anal investigation is hardwired canine communication. Punishment creates anxiety and damages your dog's trust. Redirect and reward alternative behaviors instead.
- Manage multi-dog households — If one dog obsessively licks another's rear, ensure both dogs get adequate individual exercise (minimum 30-60 minutes daily depending on breed), mental enrichment (puzzle feeders, snuffle mats, training sessions), and separate rest areas.
Related Scent Behaviors You Might Notice
Anal licking is part of a broader suite of canine scent-investigation behaviors. You may also observe:
- Urine marking investigation — Dogs sniff and sometimes lick urine marks left by other dogs, processing the same volatile compounds through the vomeronasal organ.
- Flehmen response — Some dogs exhibit a lip-curling, open-mouthed expression after intense sniffing. This helps draw scent molecules into the vomeronasal organ.
- Rolling in strong odors — Dogs roll in feces, dead animals, and other pungent substances, possibly to mask their own scent or carry information back to their social group.
- Genital sniffing — Preputial and vulvar secretions also carry identity and reproductive information; dogs investigate these areas for the same reasons they investigate anal glands.
Frequently Asked Questions
Why do dogs lick asses specifically instead of just sniffing?
Licking provides both olfactory and gustatory input simultaneously. The moisture from the tongue helps dissolve volatile compounds and carry them to the vomeronasal organ more efficiently. Some dogs are more "tactile" investigators and naturally progress from sniffing to licking. It is the same information-gathering process, just with a more direct sampling method.
Can dogs actually identify individual dogs by licking their anal area?
Yes. Research confirms that the chemical composition of anal gland secretions is individually distinctive, much like a fingerprint. Dogs can differentiate between familiar and unfamiliar dogs based on these secretions alone, even without visual or auditory cues.
Is it safe for my dog to lick another dog's anal area?
In general, yes — the risk of disease transmission through brief anal licking is low. However, if the other dog has an active anal gland infection, perianal abscess, or intestinal parasites, there is a small risk of bacterial or parasitic transfer. Keeping both dogs current on parasite prevention (monthly heartworm/intestinal parasite preventives costing $15-$30/month) minimizes this risk.
What does it mean when my dog licks my crotch area?
Your dog is investigating your apocrine sweat glands, which are concentrated in the human groin and produce steroid-based compounds similar to canine pheromones. Your dog can detect information about your hormonal state, stress levels, and even certain medical conditions through these secretions. It is the human equivalent of two dogs sniffing rear ends — socially awkward but biologically motivated.
My dog licks their own anus constantly — should I be worried?
Persistent self-licking of the anal area is a common sign of anal gland impaction, allergies, parasites, or perianal skin infection. If the behavior continues for more than 24-48 hours, or if you notice scooting, swelling, discharge, or signs of pain, consult your veterinarian. These conditions are treatable but can worsen without intervention.
How do I stop my dog from licking other dogs' rear ends at the dog park?
You should not try to eliminate this behavior entirely — it is essential canine communication. Instead, manage duration: allow 3-5 seconds of investigation, then use a trained "let's go" or "leave it" cue to redirect. Reward compliance with a high-value treat. Consistent positive reinforcement training over 4-6 weeks will give you reliable control without suppressing your dog's natural social behavior.
Understanding why dogs lick the anal area ultimately comes down to recognizing that dogs experience the world through a sensory channel that humans barely possess. What seems crude or embarrassing to us is, for dogs, a sophisticated and essential form of social communication — one that has served canids well for millions of years. Your role as an owner is not to eliminate the behavior but to understand it, manage it when socially necessary, and recognize when it crosses from normal communication into a sign that your dog needs veterinary help.
Jonas Cole
All our authors care for dogs every day — read more of their work on the authors page.
