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  • Jo De Klerk

    Dog Lumps and Bumps - The Causes And What To Look Out For

    Most dog owners at some point in their dog’s life will have a moment of panic when they find a lump on their beloved pet. Lumps are extremely common on dogs and can be as benign as a wart or as sinister as cancer. Therefore, it’s important to understand what to look out for to understand when a vet visit is needed.

    What are the main causes of lumps on dogs?


    Lumps caused by a local infection will go down as quickly as they came up. They can easily be caused by a small thorn getting embedded in the skin on a walk, or an infected tick bite, amongst many other causes.

    The lump is caused by an influx of inflammatory white blood cells into the area. The normal tissues cannot hold this number of cells, and therefore, since the skin is stretchy, it expands to accommodate them. As a result, a lump appears. Sometimes these white blood cells pool together to create an abscess, which if it is big, your vet may need to lance and drain it. Usually, small local infections can easily be dealt with by your dog’s own immune system, however, occasionally they may need antibiotics from the vet to heal it up.


    Cysts are fluid-filled structures within the skin layer. They can be as small as a pimple or as big as a plum. Most cysts in the skin originate from sebaceous glands which produce an oil-like substance. They are triggered when the gland becomes blocked.

    Cysts are simply a local nuisance, and not cancerous, so just because your dog has one, does not mean it will spread around the body. They are, however, sometimes difficult to treat, as draining the cyst does not eliminate the problem, and it will frequently fill back up again. Often, if they are large in size, they will need to be surgically removed.

    Warts and Skin Tags

    Warts and skin tags are extremely common on dogs and are completely harmless. They both look very similar and sometimes it is difficult to differentiate between the two. Both warts and skin tags are small lumps, of only a few millimetres. The main differences are that skin tags seem to dangle, whereas warts have a thicker base to them, also skin tags will always remain, whereas warts may slowly subside.

    The cause for skin tags is up for debate, however, some people believe it is from inflammation in the skin, overbathing your dog, or skin irritants. However, the reality is that they often occur randomly. Warts, on the other hand, are caused by a virus, however, there is no need to see your vet if you find a wart on your dog.


    Most people when they hear the word ‘tumour’ they immediately think of ‘cancer’, but not all lumps are nasty. For example, a common lump seen on dogs is a lipoma, which is a benign tumour originating from fat cells. These lumps can grow locally and may cause problems if they interfere with joints, but they will not threaten the life of your dog. Nevertheless, some tumours can be much more aggressive, and therefore it is always best to get them checked out by a vet.

    So, what are the signs of a benign or malignant tumour? The table below outlines the key points to look out for, although there will still be some exceptions.

      Benign Malignant
    Growth Slow growing

    Fast growing






    Either non-painful or painful

    Hair growth

    Hair present




    None or broken skin


    Free moving

    Attached to underlying structures


    Well defined, e.g. spherical

    Well defined or diffuse e.g. irregular



    Anywhere, including on the limbs

    Your vet will be able to determine the type of tumour by placing a needle into the lump and aspirating some cells. These cells can be put onto a slide and analysed under a microscope. If the tumour appears sinister under the microscope, then removal is usually the course of action. Sometimes an X-ray of the chest and abdomen is taken before surgery, to ensure it hasn’t spread anywhere else in the body.

    Removal of the lump is usually a day procedure, and the process has been described in Ask Dr Jo: My dog needs a lump removed .If the lump could potentially be aggressive, your vet will need to take a wide margin around it of at least 2cm, which means that underlying muscle may need to be taken out too. Most surgical sites heal very well, but there are some circumstances which may make healing more complicated. For example, a large tumour would leave a big void, and therefore there is potential for fluid to build up in the site. Also, a tumour removed from a mobile area may lead to slower healing of the incision because of constant movement. Therefore, following your vet’s advice for post-surgical care is vital.

    If caught early enough, removal of a tumour can be curative, however, if the tumour has already spread, then chemotherapy or radiotherapy might be indicated. Most vet practices will be able to offer chemotherapy, but radiotherapy must be undertaken in specialist hospitals.

    What is the take-home message?

    First of all, do not panic. There are many causes of lumps on dogs, and many of them are not of serious concern. Nevertheless, it is wise to get any lump checked out by a vet, as some lumps can be cancerous. That way, by just a simple test that can be done at your vet practice, it is easier to understand the prognosis and course of action to take.

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    Jo De Klerk

    Jo is a graduate of the Royal Veterinary College, London. She has a Masters degree in Tropical Animal Health, and has spent most of her career working in mixed veterinary practice.

    Recently, she has become involved in one of the UK’s fastest growing veterinary telemedicine services for dogs and cats.

    She is a published author of several books, and enjoys working as a freelance veterinary writer around her clinical work.

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