Why Dogs Sniff Each Other’s Rear Ends

ImmunityQ&AMeongsiljang Veterinary Advisory Board

Dogs sniffing each other’s rear ends is a natural greeting behavior that allows them to gather information about one another through anal gland secretions. We’ll also let you know when to be concerned.

Why Do Dogs Sniff Each Other’s Rear Ends?

Two dogs greeting each other in the park by sniffing each other's rear ends

When dogs sniff each other’s rear ends, they’re using secretions from the anal sacs—small glands located on either side of the anus—to gather information about the other dog’s sex, age, health status, and even mood. This is a normal, natural behavior, akin to humans shaking hands or exchanging business cards when meeting for the first time. Rather than trying to stop it, it’s best to let this form of communication happen naturally. However, if the odor is unusually foul or if your dog scoots its hindquarters along the floor, these could be signs of an anal sac issue, and a veterinary checkup is recommended.

Anal Sacs: A Dog’s “Scent Business Card

The anal sacs are almond-sized glands located on either side of the anus at the 4 o’clock and 8 o’clock positions. They contain a thick, oily secretion that carries a dog’s unique scent profile—much like a fingerprint or identification number in humans. When another dog sniffs this area, it can instantly recognize the individual and assess its current condition. This is why dogs often greet each other by sniffing each other’s rear ends before making face-to-face contact.

Information Gathered from a Single Sniff

Dogs have an exceptionally keen sense of smell, allowing them to extract a wealth of information from secretions with just a brief sniff. In veterinary behavioral science, these olfactory signals are broadly categorized into "identification signals" that reveal who the individual is, and "status/emotional signals" that convey their current state and feelings.

Sex and neuter status: The scent of secretions varies depending on sex and reproductive status.

Age group: Each age range has a distinct odor, helping dogs identify whether another dog is a puppy.

Individual identification: Secretions carry a unique scent specific to that individual dog.

Estrus status: The estrus status of female dogs can be detected through scent.

Mood and stress level: The scent released changes when a dog is stressed.

Therefore, even a quick 1- to 2-second sniff allows a dog to gauge whether it’s safe to play with the other dog.

An illustration depicting how a dog’s nose reads various pieces of information through scent.

Human Greetings vs. Dog Greetings

Item	Humans	Dogs
First greeting method	Face-to-face and a handshake	Sniffing the rear
Information exchanged	Name, occupation	Sex, age, health, mood
Time it takes	Tens of seconds to a few minutes	Usually 1–5 seconds
Is it rude behavior?	Touching without the other's permission is rude	A natural social behavior

A dog sniffing another's rear is not rude behavior but normal communication

What If Only One Dog Tries to Sniff?

If one dog persistently pushes its nose toward the other while the latter tucks its tail and tries to avoid contact, this may indicate an attempt to establish dominance or a signal of discomfort. In such cases, it’s best to briefly separate them. If the avoiding dog growls or shows its teeth, the owner should gently pull on the leash to defuse the situation. Not all dogs are comfortable with scent exchanges with unfamiliar dogs.

If You Notice These Odors, It May Be an Anal Sac Issue

If your dog’s anal glands emit an unusually strong fishy or pus-like odor, or if you notice scooting (dragging the hindquarters on the floor) and repeated licking of the area, suspect anal sacculitis or anal sac rupture. In severe cases, the skin around the anus may become red, swollen, or develop an opening. Do not attempt to treat this at home; instead, visit a veterinary clinic for professional anal gland expression and anti-inflammatory and antibiotic therapy.

Sniffing Human Buttocks and Legs Is for the Same Reason

This behavior is also at play when a dog sniffs between a person’s legs or near their buttocks. Human skin and sweat emit a variety of scent signals, and dogs use their highly developed sense of smell to interpret these cues, trying to determine who the person is, their current state, and whether they’ve been in contact with other animals. This isn’t rude behavior; it’s often an expression of friendliness and curiosity. However, since guests may feel uncomfortable, it’s best to gently manage the behavior using commands like “sit” or “wait.”

A dog sniffing a guest’s legs at the front door

Should You Stop This Behavior During Walks?

In general, it’s fine not to intervene. Brief scent exchanges help with socialization. However, please step in if any of the following occur:

Puppies who haven’t completed their vaccinations: They’re at risk of infectious diseases.

One dog growling: This could escalate into a fight.

Sniffing lasting more than 10 seconds: This may signal that one dog is feeling stressed.

The other dog is a large, aggressive breed: Don’t ignore warning signs.

If none of these situations apply, avoid over-managing and simply observe the natural interaction between the dogs.

Pay Special Attention If Vaccinations Are Not Complete

Young puppies whose vaccination schedules are not yet complete are especially vulnerable to infectious diseases because their immunity has not fully developed. Their immune systems are still immature, and while maternal antibodies (maternally derived antibodies) remain in their bodies, their response to vaccines is also weak. Therefore, until their immunity is properly established, it is safer to avoid direct contact with unfamiliar dogs and instead focus on "socialization" by holding them in your arms and gradually exposing them to external stimuli. Even if vaccinations are completed before six months of age, a booster shot around six months is recommended, so please consult with your veterinarian to confirm the exact completion date of the vaccination schedule.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

My puppy keeps sniffing my butt. Is this strange behavior?

That’s completely normal. For dogs, that area is where they pick up the most information, so it’s a way of expressing excitement and curiosity. If it becomes uncomfortable, gently redirect them with a “sit” command.

My dog growled as soon as I smelled his butt. Why did he do that?

They may have picked up on warning signals in the scent—such as stress, illness, or estrus—or felt threatened because the other animal came too close. Please separate them immediately.

My dog has a strong fishy odor. Will bathing solve the problem?

A bath alone won’t solve the problem. Since anal gland secretions often leak out, your pet will need to have the glands expressed or receive anti-inflammatory treatment at a veterinary clinic.

Can I express my dog’s anal glands at home?

If inexperienced owners squeeze the anal glands incorrectly, it can lead to rupture or inflammation. It's best to start by learning the proper technique at a veterinary clinic or grooming salon, and if it seems difficult, leave it to the professionals for safety.

Does neutering reduce scent-marking behavior?

While the drop in hormones may reduce behaviors like sniffing for signs of heat, the basic instinct to greet through scent remains intact. It doesn’t disappear completely.

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References

[1] Horowitz A., Inside of a Dog: What Dogs See, Smell, and Know, 2012

[2] Tobias KM. et al., Anal Sacculectomy, Veterinary Surgery Small Animal, 2017

[3] Introduction to Animal Behavior and Veterinary Behavioral Medicine, Ch.3 Olfactory Communication