Why Are My Dog's Testicles Swollen? (Causes and Red Flags)

Swelling in a male dog's testicles or scrotum can come from infection or inflammation, a bite or blunt injury, an allergic reaction, fluid building up around the testicle, a hernia pushing abdominal contents into the scrotum, a twisted spermatic cord, or a mass growing inside the testicle itself. Any new lump or swelling should be checked by a vet. These causes look alike from the outside, and some of them are time-critical: a male dog straining to pee or unable to pee is an emergency, see a vet now, and so is a scrotum that has suddenly become swollen, hot or painful.

This page walks through what a normal scrotum feels like, the range of things a vet works through when the area swells, the signs that mean same-day care, and how the cause actually gets identified. It is not a way to diagnose your dog at home. It is a way to arrive at the appointment knowing what to describe and what questions to ask.

What normal looks like, and what counts as swelling

In an intact adult dog, the scrotum sits below and behind the back legs and holds two testicles of roughly similar size and shape. They should feel smooth and firm but not hard, move freely within the sac, and cause no reaction when handled gently. The skin over them is thin, lightly haired, and close to the same temperature as the rest of the dog.

Owners usually notice one of a few changes. One side looks bigger than the other. The whole sac looks stretched, shiny, red or bruised. The skin feels hot. The dog licks the area constantly, sits down hard and then shifts, walks with a wide stance, or flinches when it is touched or when he jumps into the car.

It is worth knowing that the swelling is not always the testicle. The scrotal skin can swell on its own from a sting, a scrape, a burn from hot pavement, or a contact irritation, with normal testicles underneath. Fluid can collect in the sac around a testicle. In a hernia, what you are feeling may be fat or a loop of intestine that has slipped down from the abdomen. And in a neutered dog, the empty scrotal sac remains and can swell after surgery or later in life. A vet separates these by feel and by imaging, not by appearance.

If your dog has only one testicle in the scrotum, mention that at the appointment. A retained testicle sits in the abdomen or groin instead, and it changes what a vet looks for when something swells.

Reasons a vet will work through

No single sign points to one cause. The table below groups what a vet considers against what an owner tends to see at home.

Possible cause	What an owner might notice	Urgency
Inflammation or infection of the testicle or epididymis	Hot, firm, painful swelling, fever, low appetite, reluctance to move	Same day
Bite wound, blunt trauma or bruising	Sudden swelling after a fight, fall or rough play, puncture marks, bleeding	Same day
Scrotal skin irritation, burn or dermatitis	Red, raw or crusted skin, heavy licking, testicles feel normal underneath	Prompt appointment
Insect sting or allergic reaction	Rapid puffy swelling, hives elsewhere, facial swelling, itching	Urgent if breathing or face is involved
Inguinal or scrotal hernia	Soft bulge that may change size, vomiting or pain if it becomes trapped	Urgent
Twisted spermatic cord (torsion)	Sudden severe pain, tense swelling, vomiting, dog will not settle	Emergency now
A mass in the testicle	Slow change in size or firmness, often with little pain, one side harder than the other	Prompt appointment
Fluid accumulation around the testicle	Soft, fluid-feeling swelling, sometimes with swelling elsewhere on the body	Prompt appointment
Bleeding or clotting problems, including tick-borne infection	Bruised-looking scrotum, bruising elsewhere, lethargy, pale gums	Same day
Prostate or urinary disease noticed alongside	Straining, dribbling, blood in urine, difficulty passing stool	Emergency if he cannot urinate
Recent neuter surgery	Swelling, firmness or bruising of the empty sac after the procedure	Call the surgical clinic

A few of these deserve more detail.

Inflammation and infection. Bacteria can reach the testicle from a bite wound, from the urinary tract, or through the bloodstream. These dogs are often genuinely unwell, with fever and pain rather than swelling alone. Vets also test for transmissible infections that can settle in the reproductive tract, which matters for breeding dogs and for other animals in the household.

Hernias. The inguinal canal is a natural opening in the body wall. If it is wider than it should be, fat or intestine can slide through and sit beside the testicle. A hernia that becomes trapped cuts off its own blood supply, and that dog becomes painful and sick quickly.

Torsion. The testicle hangs from a cord carrying its blood supply. If that cord twists, circulation stops. The pain is sudden and severe, and this is one of the situations where hours matter. Dogs with a retained testicle are a particular concern because the twist happens inside the abdomen, where you cannot see it.

Masses. A lump within a testicle is more often seen in older intact dogs and in retained testicles. Some change the dog's hormone balance, producing hair loss on the flanks, darkened skin, enlarged nipples, or other male dogs showing unusual interest in him. A mass cannot be identified by look or feel. Only sampling the tissue, through a needle sample or after surgical removal, can say what it is, and that is a conversation to have with your vet rather than something to guess at from a photo online.

Red flags that mean emergency care, not a wait and see

A scrotum that is suddenly swollen, hot or intensely painful, a dog who is straining to urinate or cannot urinate, or any suspicion of a twisted testicle means emergency veterinary care now, not in the morning.

Go in immediately if you see any of the following:

• Sudden swelling with obvious pain, crying out, or refusing to sit or walk
• Straining in the urination posture with little or no urine coming out
• Vomiting, a tense or painful belly, or collapse alongside the swelling
• An open wound, puncture, heavy bleeding or discharge from the scrotum
• Hot skin plus fever, shivering, or a dog who will not eat or stand
• Pale or grey gums, or bruising appearing elsewhere on the body
• Rapidly spreading puffiness with facial swelling, hives or laboured breathing
• Any swelling in a dog known to have a retained testicle

Book a prompt appointment, even without those signs, for swelling that has crept up over days or weeks, firmness on one side only, skin changes, constant licking, or any change in fertility or behaviour in a breeding dog. Slow and painless does not mean harmless. It usually means the cause is one that gives you a little more time, not none.

How the cause actually gets identified

The appointment starts with a hands-on exam. A vet compares both sides, checks temperature, feels the testicles, the epididymis and the cord separately, looks at the skin, checks the inguinal area for a hernia, and often examines the prostate and lymph nodes as well.

From there, the work-up depends on what that exam finds. Ultrasound of the scrotum is the usual next step because it shows whether swelling is the testicle itself, fluid around it, blood supply, or abdominal contents that have moved down. Urine testing and blood work look for infection, inflammation, clotting problems and organ disease. Testing for transmissible reproductive infection and for tick-borne infection may be added. If there is a mass, sampling it is what gives an answer, and abdominal imaging may be used to look at a retained testicle or at the lymph nodes that drain the area.

You can make that process faster. Before you go, note when you first saw the change, whether it has grown, whether your dog is eating and urinating normally, whether he has been in a fight or had a fall, whether he is intact or neutered and when, any breeding history, and any tick exposure or travel. Photographs taken a few days apart are genuinely useful.

While you wait for the appointment, keep it simple. Do not squeeze, massage, poke or try to reduce a bulge yourself, and do not put human creams, ointments or antiseptics on the skin. Keep him quiet and discourage licking. If you are not sure whether what you are seeing can wait, talk to your vet and describe it rather than deciding alone.

What usually happens after the diagnosis

Treatment follows the cause, so there is no single answer here. Some dogs are managed medically with a course prescribed and monitored by the vet. Some need surgery, whether that is repairing a hernia, exploring a twisted cord, or removing an affected testicle. Neutering is often part of the plan when the testicle itself is involved, and in infectious cases there may be implications for other dogs in the home. Pain relief is a veterinary decision in every one of these situations, and human painkillers are dangerous to dogs.

Recovery varies too. Results vary from dog to dog, and the follow-up schedule your vet sets, including recheck exams and repeat imaging, is part of the treatment rather than an optional extra.

Key takeaways

• Swelling can be infection, injury, skin irritation, an allergic reaction, fluid, a hernia, torsion or a mass, and the outside appearance does not distinguish them.
• Sudden, hot, painful swelling, straining to urinate, vomiting or collapse means emergency care the same hour.
• Slow, painless firmness on one side still needs an appointment, especially in an older intact dog.
• A retained testicle raises the stakes, because torsion and masses in that testicle are hidden from view.
• A lump can only be identified by sampling the tissue, never by sight, feel or photograph.
• Do not squeeze the area, apply home products, or give any human medication while you wait.

Your veterinarian owns the diagnosis and the treatment plan here. They have the exam findings, the imaging, the laboratory results and your dog's history in front of them, and those four things together are what turn a swollen scrotum from a frightening unknown into a named problem with a defined next step. If something about your dog's testicles has changed, the right move is a phone call today, not a week of watching.

For a broader list of warning signs that mean a same-day or emergency visit, see Dog Emergency Signs. Related reading on this site covers facial swelling and allergic reactions in dogs, and what owners should know about new lumps.