Your dog probably doesn’t have an “extra” nipple at all. Dogs typically have 8 to 10 nipples, but the number varies naturally, with some dogs having fewer and others having more. An odd number is also completely normal, which can make one side look like it has a bonus. In most cases, what looks like an extra nipple is just part of your dog’s standard anatomy.
How Many Nipples Dogs Normally Have
Dogs have two parallel rows of mammary glands running from the chest down to the groin, with four or five glands on each side. That means most dogs land somewhere between 8 and 10 nipples total, but counts outside that range aren’t unusual. Some dogs have 6, others have 12. The number isn’t strictly tied to breed or size, and it’s set during fetal development when the two “milk lines” form along the belly.
The rows are generally symmetrical, but not always perfectly so. One chain might have five nipples while the other has four, leaving a lone nipple with no match on the opposite side. This is the most common reason owners suddenly notice what they think is an extra one, especially on a short-haired dog where the belly is easy to see.
Both male and female dogs have nipples. Males develop them in the womb before sex differentiation occurs, just like in humans. A male dog can have the same range of nipple counts as a female, and an odd or seemingly extra nipple on a male dog is equally harmless.
What a True Supernumerary Nipple Is
The medical term for a genuinely extra nipple is polythelia. It’s considered an example of atavism, meaning it’s a throwback trait from ancestral anatomy. During fetal development, the tissue along the milk lines sometimes leaves behind small remnants that develop into additional nipples. These form during the third month of development in the womb and are present from birth.
A supernumerary nipple looks and feels like any other nipple. It sits somewhere along the milk line (the path from chest to groin), has the same color as the surrounding skin or nearby nipples, and is flat or slightly raised. It doesn’t grow, change color over time, or cause discomfort. In dogs, polythelia is so common that most vets consider it a normal variation rather than a medical finding.
How to Tell a Nipple From a Lump
The real concern behind this search is usually less about counting nipples and more about a bump on your dog’s belly that you’re not sure about. Here’s what helps you tell them apart.
A nipple, even an extra one, is small, round, and sits flush with or slightly above the skin. It has a consistent texture and matches the other nipples in color and size. It falls somewhere along the two lines running down your dog’s underside. If you gently part the fur and compare it to a known nipple nearby, the resemblance is usually obvious.
Other common bumps look different in specific ways:
- Skin tags hang off the skin on a narrow stalk and often have a rough, wart-like surface. They’re common in older dogs and large breeds.
- Ticks are dark brown or gray, feel firm, and have tiny legs visible at the base if you look closely. They’re attached to the skin rather than part of it.
- Warts have a bumpy, cauliflower-like texture that looks nothing like a smooth nipple.
- Skin tumors tend to be dome-shaped, firm, and sometimes hairless or ulcerated. They can appear anywhere on the body, not just along the milk lines. Some are dark-colored or look like blood blisters.
Location is one of the most useful clues. A bump that falls neatly in line with your dog’s other nipples is almost certainly a nipple. A bump on the leg, side, ear, or neck is not.
Signs That Something Needs Attention
A normal nipple, whether it’s the 8th or the 11th, just sits there quietly. What warrants a closer look is any nipple or nearby tissue that starts changing. The key warning signs are redness, swelling, or pain around a mammary gland, any discharge (milk, blood, or pus) when your dog isn’t nursing, a firm lump beneath or next to a nipple, and open sores or ulcers on the skin around the gland.
Mammary tumors are common in dogs, particularly in females who were spayed later in life or not spayed at all. These tumors often affect more than one gland at a time, with 50 to 70 percent of cases involving multiple glands. They feel like firm masses under or near the nipple, distinctly different from the nipple itself. Mastitis, an infection of the mammary gland, causes obvious swelling, redness, and pain that your dog will react to when touched.
If the bump you found is soft, flat, painless, the same color as your dog’s other nipples, and sitting right along the belly’s midline, you’re almost certainly looking at a perfectly normal nipple your dog has had since birth. You just hadn’t noticed it before.