Mammary (breast) problems in dogs: an overview


  • Mammary (breast) problems are most common in female dogs that haven’t been speyed.
  • Signs of a problem tend to include swelling, redness, an obvious lump, or discharge from the nipple.
  • Most mammary problems can be treated, but left without veterinary help, can get worse and become harder to treat.
  • Contact your vet if your dog has a mammary problem.

General information

Although mammary problems can affect any female dog, they are most common in those that haven’t been speyed. This is because mammary problems are usually linked to hormones or pregnancy. Most mammary problems can be treated, but if your dog is left without veterinary help, the problem could get worse, become more serious or possibly even life threatening.


The most common symptoms of mammary problems include:

  • Red, swollen or painful mammary gland(s)
  • Mammary lump(s)
  • Unexpected milk, blood, or pus from the mammary glands
  • Wounds or ulcers



Mastitis is inflammation and infection in a mammary gland. It’s a very painful condition that causes swelling, redness, and often discharge from the nipple. Mastitis is most common in lactating dogs, and those having a phantom pregnancy. Left untreated, mastitis infections can spread around the rest of the body and cause severe illness.

Phantom pregnancy

During a false pregnancy, the mammary glands can become swollen and produce milk.

Mammary lumps

There are a few different types of mammary lump, some harmless and some cancerous. It’s important to get any new lumps checked by your vet before it causes a problem, or potentially spreads elsewhere in the body.

Skin lumps

Skin lumps in the mammary region should always be checked by your vet.

Wounds or ulcers

Wounds, ulcerations and weeping sores on a mammary gland tend to develop if there is another underlying problem (such as mastitis, phantom pregnancy or a lump).

When to contact your vet

It’s important to get your dog checked by your vet if you notice any changes to their mammary glands, especially if you notice any redness, swelling or new lumps.


It’s not possible to protect your dog from all mammary problems but you can reduce the risk of some by neutering your dog.

Consider insuring your dog as soon as you get them, before any signs of illness start. This will ensure you have all the support you need to care for them.

Published: October 2020

Written by vets and vet nurses. This advice is for UK pets only. Illustrations by Samantha Elmhurst.