Cutaneous histiocytosis is a skin disease in which many firm bumps and raised patches form in the deeper layers of a dog’s skin and the tissue just under it. The bumps are made of activated immune cells called histiocytes (dendritic cells) [1][2]. Vets also call it cutaneous reactive histiocytosis, because the cells are reacting rather than growing as a cancer [1][2]. In one study of 32 affected dogs, the median age when signs began was 4 years [3].
Have your vet check any dog that has several skin bumps at once. Only a tissue sample can show what the bumps are [1].
A single bump in a young dog may be a different tumor, the histiocytoma. See histiocytoma in dogs.
Which dogs get it
Dogs of many breeds and mixed breeds have been reported with it [1]. In the 32-dog study, half of the dogs were 4 years old or younger when it started [3]. The cause is not fully known. Researchers think the immune system is not regulated properly, and genes may play a part [1][2].
What the bumps look like and where
- Many bumps: firm lumps (nodules) and flat raised patches (plaques) in the skin, often several at a time. The skin over them may be red or lose hair [1][3].
- They come and go: the disease tends to flare up and settle down, and the bumps sometimes clear without treatment [1].
- Where: the head and face, the body and the legs [1][3]. The nose and nostrils can swell, redden or lose color [3]. Dogs with lesions in the nose may sneeze or breathe noisily [1].
- Sores: some patches open in the middle and form sores [1].
In the cutaneous form, the disease stays in the skin, the tissue under it and the nearby lymph nodes [1].
Not the same as systemic or malignant histiocytosis
In systemic reactive histiocytosis, the same skin bumps appear, but the disease also reaches other parts of the body, such as the inside of the nose or mouth, the eyes or internal organs [1][2]. Malignant histiocytosis (histiocytic sarcoma) is a cancer and a different disease [2]. Your vet may suggest blood tests and scans to look for disease beyond the skin [1]. Your vet can tell you which one your dog has.
How vets diagnose it
Your vet will examine the bumps and take a biopsy, a small piece of tissue that is checked under a microscope [1]. The pathologist looks for a typical pattern of histiocytes deep in the skin [1]. Your vet also needs to rule out look-alike problems, such as infections and a type of skin lymphoma [1]. Your vet will also look inside the mouth, since the mouth can be affected too [1].
Treatment
Your vet will advise on treatment. Most dogs are treated with medicines that calm the immune system, and some dogs need ongoing treatment to keep the bumps away [1][3].
At home, as directed by a vet:
- note where the bumps are and when they appear or go, so you can show your vet;
- tell your vet if your dog sneezes, breathes noisily or if a bump opens into a sore [1];
- go back for every recheck.
Outlook
In the 32-dog study, the skin bumps cleared in every dog after the first treatment. Nine dogs had the bumps come back, and dogs with lesions on the nose were more likely to relapse [3]. Because the disease can settle on its own, it is hard to judge how well a treatment works [1].
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:
- several firm bumps or raised patches in the skin [1][3];
- bumps on the legs, body, head or face [3];
- swelling or color change on the nose, or sneezing or noisy breathing along with skin bumps [1][3];
- a bump that opens into a sore [1].
FAQ
Is cutaneous histiocytosis cancer?
No. Researchers describe it as a reactive, non-cancerous growth of immune cells [1][2]. Your vet will explain what the sample shows for your dog.
Is it the same as a histiocytoma?
No. A histiocytoma is a tumor and a separate disease [2]. Cutaneous histiocytosis causes many bumps that can come and go [1]. See histiocytoma in dogs.
Can the bumps come back?
Yes. In the 32-dog study, some dogs relapsed, more often those with nose lesions [3]. Go back for every recheck.
The bottom line
Cutaneous histiocytosis is a non-cancerous immune disease that causes many firm bumps and raised patches in a dog’s skin, on the head, face, body and legs and sometimes the nose. The bumps tend to come and go, and in this form the disease stays in the skin and nearby lymph nodes. A biopsy shows what the bumps are. Most dogs respond to treatment, but the bumps can come back.
This article is for general information only and does not replace advice from your veterinarian. If your dog has several skin bumps, see your vet.
Sources
- Cain CL, Lowe A, Mauldin EA. Treatment of Reactive Histiocytosis With Oclacitinib: A Retrospective Case Series of 10 Dogs. Veterinary Dermatology 2026;37(3). CC BY 4.0. https://doi.org/10.1111/vde.70048
- Affolter VK, Moore PF. Canine cutaneous and systemic histiocytosis: reactive histiocytosis of dermal dendritic cells. American Journal of Dermatopathology 2000;22(1):40-48 (abstract, PubMed). https://pubmed.ncbi.nlm.nih.gov/10698216/
- Palmeiro BS, Morris DO, Goldschmidt MH, Mauldin EA. Cutaneous reactive histiocytosis in dogs: a retrospective evaluation of 32 cases. Veterinary Dermatology 2007;18(5):332-340 (abstract, PubMed). https://pubmed.ncbi.nlm.nih.gov/17845621/