Not every growth on a dog that looks like a wart is a wart. True warts (papillomas) are caused by a virus. Some other growths can look similar but have different causes, such as benign tumors that start near the top of the hair follicle [1] or rare inherited skin changes called epidermal nevi [4]. For true warts, see warts and papillomas in dogs and cats.
Many kinds of growth can look alike on the outside, so a vet needs to check each one. Lab tests on a sample are what tell them apart [2][3].
Have your vet check any new growth on your dog’s skin.
Epidermal nevi (hamartomas)
An epidermal nevus is a patch of overgrown skin, not a cancer. In dogs these are rare. Researchers have traced some cases to a change in a single gene, and in one reported dog the patches kept spreading over time [4]. Some forms show up as dark, raised plaques [4]. Because they can look like warts or other lumps, your vet may take a sample to find out what they are.
Other rare benign growths
A few other rare, benign growths that start near hair follicles or glands can also look like warts. They are uncommon, and only a lab exam of a sample can name them. Your vet will tell you if your dog has one and what to do about it.
Keratoacanthomas (infundibular keratinizing acanthomas)
This benign tumor has several names, including infundibular keratinizing acanthoma, keratoacanthoma and intracutaneous cornifying epithelioma [1]. It grows from the top of the hair follicle, near the skin surface, so it often has a small pore on the surface. It can appear as one lump or as several firm, rounded lumps with a plug of keratin, the tough protein in skin and hair, in the middle [1]. That central plug can make it look a little like a small horn.
A published case review notes that these tumors are seen in young and middle-aged dogs, and more often in males [1]. In a lab study of skin tumors from dogs in Portugal, they made up a small share of all skin tumors, were often found on the back, neck and hind legs, and German Shepherds were among the breeds most often affected [5]. For other tumors that start in the hair follicle, see hair follicle and basal cell tumors in dogs and cats.
Some dogs scratch, rub or chew at a lump. A broken or open lump can become sore and infected, so tell your vet if this happens.
How vets diagnose them
Your vet may use a fine needle to draw cells from the growth (fine needle aspiration) and look at them under a microscope. In a study of skin and under-skin lumps in dogs and cats, this test agreed with the final lab result in most cases [3]. For some growths that start in the hair follicle, though, the cells look much alike, and a biopsy, where a small piece of tissue is removed and sent to a lab, is usually needed to tell them apart [2]. The lab result tells these growths from warts and from other lumps. For other lumps, see lumps and bumps on dogs.
Treatment
Your vet will advise on treatment for your dog. The choice depends on what the growth is, where it is, and whether it bothers your dog or gets hurt or infected. In the published case of a young dog with several keratoacanthomas, the lumps were removed by surgery and had not come back at the eight month check [1]. Some of these growths are only watched, with rechecks [1].
At home, as directed by a vet:
- note the size, place and date of any growth, so you can show your vet any change;
- never tie off, cut, squeeze or pick at a growth;
- go back for every recheck.
Outlook
The growths in this article are benign, which means they do not spread to other parts of the body [1][4]. Some dogs get more than one keratoacanthoma [1], and some forms of epidermal nevi can keep spreading over the skin [4].
These are statements about groups of dogs. They cannot predict how one dog will do. Your vet can explain what this means for your dog.
When to see your vet
See your vet if your dog has:
- a new wart-like growth;
- dark, raised patches on the skin, especially in a young dog;
- a lump with a plug or pore in the middle, or one that looks like a small horn;
- a growth your dog scratches, rubs or bites at;
- a growth that is open, sore or looks infected.
FAQ
Are these the same as warts?
No. True warts are caused by a virus. The growths in this article have other causes, even if they look alike. Only your vet can tell which one your dog has.
The bottom line
Some wart-like growths on dogs are not viral warts. Epidermal nevi are rare patches of overgrown skin, and keratoacanthomas are benign hair follicle tumors that often have a keratin plug in the middle and can look like a small horn. They are benign, but only a vet can tell them from warts and other lumps, and your vet will advise on treatment.
This article is for general information only and does not replace advice from your veterinarian. If your dog has a new skin growth, see your vet.
Sources
- Tavasoly A, Gholami H, Rostami A, et al. Clinico-histopathologic and outcome features of cutaneous infundibular keratinizing acanthoma: a case report and literature review. World Journal of Surgical Oncology. 2014;12:173. Open access, CC BY. https://pmc.ncbi.nlm.nih.gov/articles/PMC4050395/
- Adedeji AO, Affolter VK, Christopher MM. Cytologic features of cutaneous follicular tumors and cysts in dogs. Veterinary Clinical Pathology. 2017;46(1):143-150. PubMed abstract. https://pubmed.ncbi.nlm.nih.gov/28249100/
- Ghisleni G, Roccabianca P, Ceruti R, et al. Correlation between fine-needle aspiration cytology and histopathology in the evaluation of cutaneous and subcutaneous masses from dogs and cats. Veterinary Clinical Pathology. 2006;35(1):24-30. PubMed abstract. https://pubmed.ncbi.nlm.nih.gov/16511787/
- Christen M, Austel M, Banovic F, Jagannathan V, Leeb T. NSDHL Frameshift Deletion in a Mixed Breed Dog with Progressive Epidermal Nevi. Genes (Basel). 2020;11(11):1297. https://pmc.ncbi.nlm.nih.gov/articles/PMC7716214/
- Martins AL, Canadas-Sousa A, Mesquita JR, et al. Retrospective study of canine cutaneous tumors submitted to a diagnostic pathology laboratory in Northern Portugal (2014-2020). Canine Medicine and Genetics. 2022;9:2. Open access, CC BY. https://pmc.ncbi.nlm.nih.gov/articles/PMC8875941/