Lump Under the Skin After Vaccinating a Puppy

After your puppy receives a vaccination, you may notice a number of side effects. These include fatigue, irritability or loss of appetite. These behaviors may last for up to a day after the vaccination. While your vet probably warned you about these common side effects, he may have forgotten to mention the potential appearance of a vaccination lump. After a vaccination, many puppies form a small lump at the injection site. This is not a cause for concern, but you should speak to your veterinarian if the lump seems excessively large or painful.

  1. Vaccination Bump Characteristics

    • Vaccination bumps range from the size of a pea to a marble, rest under the skin and are easily movable. They are harmless, painless and should not raise alarm in either the puppy or their owner. If your puppy seems to have a vaccination lump, monitor it for a few weeks. If it does not grow or change color, your puppy does not require veterinary attention. Lumps appearing at a point other than the vaccination site are unrelated to the vaccine and should be examined by a vet.

    Vaccination Bump Causes

    • Vaccination bumps are caused by scar tissue and cell inflammation. Vaccinations disrupt tissue and sometimes cause the immune system cells around the injection site to be activated, resulting in a small bump. This reaction occurs in only 2 percent of puppies, but is normal and not a cause for concern.

    Vaccination Bump Timeline

    • Vaccination bumps, also known as delayed cellular response, generally don't appear until a week or two after the vaccine was administered. After this, most disappear after three or four weeks. If your puppy's bump does not go away, do not be concerned. In some cases, the bump will never completely disappear, but will continue to get smaller over time. If your puppy is a show dog, ask the vet to vaccinate them in a discrete location. These will prevent judges from finding a vaccination bump, should one occur.

    Vaccination Bump Concerns

    • Vaccination bumps almost never threaten the health of puppies. However, if the bump grows, becomes larger than a marble, gets inflamed, becomes hardened or seems to be causing your puppy pain, it is best to take them to the vet. Also watch for skin discoloration or fur loss around the lump, which is not entirely abnormal, but should still be examined.