Sudden Lumps on a Dog Under the Skin

What to do if you notice your dog has bumps under her fur.


Petting your dog and feeling lots of new lumps or looking at your dog and seeing lots of bumps can be concerning, to say the least. It’s even more scary if the lumps under the dog’s skin seem to move.

If you find a lump on your dog, the first two things to consider are hives and bug bites, which are two common causes of sudden bumps on the skin of your dog.

Bumps from Hives

Hives appear after exposure to something your dog is allergic to. While this might be insect bites, it could also be any topical irritant, including a new shampoo, ointment, or plants he rubbed against.

Hives usually appear a couple hours after exposure, with lots of small bumps on his skin appearing suddenly. Rinsing him off may help remove some of the irritating substances if that’s the cause. Hives often disappear within a few hours without treatment.

If your dog is uncomfortable, ask your veterinarian about short-term corticosteroids or Benadryl for some relief. Many dogs look awful but don’t itch or rub.

However, if your dog begins to have difficulty breathing or is showing hives around the mouth or throat, contact your veterinarian immediately. Swelling in the mouth or throat can compromise breathing.

There good medications for seasonal allergies, if the cause is an allergen and a continued problem for your dog.

Bug Bite Bumps

Bugs can cause extensive skin lumps from bites or stings. This usually happens with large numbers of gnats or blackflies. While your dog may itch or roll, these bumps tend to clear fairly quickly without help.

However, if your dog stumbles into a nest of wasps, hornets, or bees, you may need help. Yellow jackets and other bees may swarm a dog, delivering many stings.

Your dog may require veterinary attention due to the toxins from multiple stings. Rinsing with cold water can help minor cases, but if your dog was stung multiple times or begins showing signs of moderate or severe reaction, contact your veterinarian.

Stings near the mouth or nose, swelling, difficulty breathing, lethargy or restlessness are all signs that you should seek immediate veterinary care. As with hives, stings in the mouth/nose area can cause internal swelling that makes it difficult for the dog to breathe.

Lump Under Dog’s Skin That Moves

A movable skin lump that appears to wax and wane in size may be a mast cell tumor. The skin over these lumps is generally red and irritated in appearance. Some of these cancers are static, but most will swell up if you or your dog rubs on them. The size increase is due to histamine release in the skin. Surgery is the recommended treatment, and the sooner you can get that done, the better.


  1. You should really include fatty tumors (lipomas) in this discussion. Yes, have bumps under the skin checked out, and the sooner the better, but not everything is going to be cancer, nor does everything need to be removed.

  2. My Cairn Terrier developed hives when she was about to give birth for the first time. She was so scared and didn’t know what to do, so I had to help with everything. Gave her some Benadryl and by the second pup she acted like an old pro.

  3. My 6.5 yo Basset Hound is covered with lumps. They ARE NOT lipomas. The vet tried to get some fluid from them but nothing came out. As he developed one on the tip of his tail, and it had opened up, the vet operated to take it off. At the time he was sure it was malignant and wanted to take his tail off. I said no and the lump was sent to lab. Their report was it was not malignant and that these kinds of lumps are often peculiar to Bassets. Have you heard of this?