Trichoepithelioma (Hair Follicle Tumor) in Dogs

  • Occurrence: very rare
  • Location of illness: Skin/Fur
Author: Dr. med. vet. Gisa Löwe | Last modified: 06.11.2025

A trichoepithelioma, also known as a hair follicle tumor, is a benign tumor that originates from the cells of the hair follicle in dogs. These tumors are usually harmless but can cause problems if they are numerous or in an unfavorable location.

BASICS/CAUSES:

Trichoepitheliomas arise from the epithelial cells that form the hair follicle. These tumors are well-differentiated, meaning that the tumor cells are very similar to the normal cells from which they originate. This similarity is one reason why they are generally considered benign.

The exact cause of trichoepithelioma formation is not fully understood, but genetic factors appear to play a role. Certain dog breeds have a higher predisposition to these tumors, suggesting a hereditary component. Breeds such as the Basset Hound, Dalmatian, and Miniature Schnauzer are more commonly affected.

In addition to genetic factors, environmental factors and hormonal influences may play a role. It is believed that hormonal changes, especially those related to reproduction, can influence the growth of trichoepitheliomas. This could explain why these tumors are more common in older dogs, as hormonal fluctuations occur throughout a dog’s life.

The most important facts at a glance

Trichoepitheliomas are benign tumors that arise from the hair follicles of dogs. The main causes are genetic predisposition and normal aging processes. Typical symptoms are small bumps on the skin, itching, and skin lesions. The tumors grow slowly and can cause pain if they enlarge. Diagnosis is made by a physical examination by the veterinarian, followed by fine needle aspiration or biopsy to accurately determine the tumor. In some cases, X-rays or ultrasound are used to rule out deeper tissue damage. Treatment depends on the tumor size and location. For small, asymptomatic tumors, regular monitoring may be sufficient. If the tumor grows or causes problems, surgical removal is recommended, which is usually curative. Alternatively, cryotherapy or laser therapy may be considered. The prognosis is usually very good, as the tumors do not metastasize and rarely recur after complete removal. Preventive measures are difficult because genetic factors play a role. However, regular skin checks and a healthy lifestyle can help promote overall health. Research focuses on genetic and molecular foundations, improving diagnostic procedures, and alternative treatment options to improve the management of trichoepitheliomas in dogs.

Causes

  • Genetic predisposition
  • Part of the normal aging process

Symptoms

Trichoepitheliomas typically appear as small, firm, dome-shaped cutaneous nodules. These nodules can occur individually or in groups and are often hairless or covered with a small crust. They are usually not painful and can vary from a few millimeters to several centimeters in diameter.

Although these tumors rarely cause ulcerations or bleeding, they can become infected, leading to redness, swelling, or inflammatory conditions. In some cases, the dog may lick or scratch the tumor, which can lead to further skin irritations.

Trichoepitheliomas can occur anywhere on a dog’s body but are most commonly found on the head, neck, and limbs. Due to their benign nature, systemic symptoms such as weight loss or lethargy are rarely associated with these tumors.

Diagnosis

The diagnosis of a trichoepithelioma often begins with a thorough physical examination by a veterinarian. The veterinarian will assess the size, shape, location, and appearance of the tumor and look for other skin changes or signs of infection.

To confirm the diagnosis, a fine needle aspiration or biopsy is usually required. In fine needle aspiration, a small amount of cell material is taken from the tumor and examined microscopically. A biopsy, in which a piece of tissue is removed and analyzed in a laboratory, can also be performed to determine the exact type of tumor.

In some cases, an X-ray or ultrasound may be necessary to determine whether the tumor has grown into deeper tissue layers or whether there are metastases, although this is rare with benign trichoepitheliomas.

Therapy

The treatment of trichoepitheliomas depends on various factors, including the size and location of the tumor, as well as the number of affected sites. In many cases, especially if the tumor is small and asymptomatic, a wait-and-see approach may be chosen, where the tumor is simply monitored regularly.

However, if the tumor grows, causes symptoms, or occurs in a location that could lead to complications, surgical removal is recommended. Complete excision is usually curative, as the tumors are benign and rarely recur if completely removed.

In cases where complete surgical removal is not possible, whether due to the location of the tumor or other health concerns of the dog, other treatment options such as cryotherapy or laser therapy may be considered. These methods aim to destroy the tumor tissue without performing invasive surgery.

Prognosis and follow-up care

The prognosis for dogs with trichoepitheliomas is generally very good. Because these tumors are benign, they do not metastasize and have no systemic effects on the dog’s health. After surgical removal, the risk of recurrence is low, especially if the tumor has been completely removed.

In rare cases where a trichoepithelioma grows in an unfavorable location or recurs repeatedly, regular monitoring and, if necessary, repeated treatments may be required. Nevertheless, the long-term prognosis for the affected animal usually remains positive.

Prevention

Since genetic factors play a role in the development of trichoepitheliomas, prevention of these tumors is difficult. However, selecting breeding animals without a known predisposition to skin tumors can help reduce the risk in future generations.

Regular examination of the dog’s skin by the owner can help detect tumors early, which facilitates treatment and improves the prognosis. Dog owners should inform their veterinarian about any new or changing cutaneous nodules to ensure early diagnosis and treatment.

A healthy lifestyle, including a balanced diet and regular exercise, can help strengthen the dog’s immune system and promote overall skin health. While this is not a specific prevention for trichoepitheliomas, it can help support the dog’s overall health.

Outlook on current research

Research in the field of trichoepitheliomas in dogs is constantly evolving, as the understanding of these tumors is of interest to both veterinary practice and science. Currently, many studies focus on the genetic and molecular foundations of these tumors. Researchers are investigating specific genetic mutations that can lead to the development of trichoepitheliomas to better understand which dogs may be at increased risk of developing these tumors.

Another focus of research is on improving diagnostic procedures. Although trichoepitheliomas are often diagnosed by biopsy, scientists are working to develop less invasive diagnostic methods, such as specific blood tests or imaging techniques, that could help detect these tumors early. The use of advanced imaging technology, such as high-frequency ultrasound and magnetic resonance imaging (MRI), is also being explored to increase the precision of the diagnosis.

Therapeutic approaches are another important field of research. Traditionally, trichoepitheliomas are surgically removed, but researchers are examining alternative treatment options such as targeted radiation therapy or the use of drugs that attack specific molecular targets in the tumor. These approaches may be particularly useful if the tumor is located in a place that makes surgical removal difficult.

A promising area of current research is the study of the microenvironment in which trichoepitheliomas arise. Scientists are investigating how the interaction of immune cells and tumor cells affects the growth and spread of the tumors. These findings could lead to new therapeutic strategies that use the dog’s immune system to fight the tumor.

In the long term, the goal of research is to develop preventive measures that minimize the risk of tumor development in dogs. This could be achieved through genetic tests that help dog owners better understand the risks and make informed decisions about breeding and health care. Overall, research in this area shows that a multidisciplinary approach that combines genetics, immunology, and oncology has the potential to significantly improve the management of trichoepitheliomas in dogs.

Frequently asked questions (FAQs)

  1. What is a trichoepithelioma? A trichoepithelioma is a benign tumor that arises from cells of the hair follicle. These tumors are common in dogs and can grow in various areas of the body, but most commonly in the area of the head, face, and neck.

  2. Are trichoepitheliomas dangerous in dogs? Typically, trichoepitheliomas are benign and do not pose a direct threat to the dog’s life. However, depending on their location and size, they can cause discomfort or increase the risk of infections if scratched or injured.

  3. How do I recognize a trichoepithelioma in my dog? Trichoepitheliomas often appear as firm, round cutaneous nodules or bumps under the skin. If you notice unusual cutaneous nodules or swelling in your dog, you should see a veterinarian for an accurate diagnosis.

  4. Which dogs are most commonly affected? Trichoepitheliomas can occur in dogs of all breeds, but are more commonly observed in certain breeds such as the Basset Hound, Beagle, and Cocker Spaniel. The age of the dog can also play a role, as older dogs tend to be more frequently affected.

  5. How are trichoepitheliomas diagnosed? Diagnosis is usually made by a biopsy of the tumor, in which a tissue sample is taken and examined under a microscope. Imaging techniques such as ultrasound or MRI can also be used to better understand the location and size of the tumor.

  6. Can trichoepitheliomas become malignant? Trichoepitheliomas are usually benign and do not tend to become malignant. Nevertheless, close monitoring is important, as there are rare cases in which the growth pattern may change. Regular veterinary check-ups are therefore advisable.

  7. What are the treatment options for trichoepitheliomas? The most common treatment is surgical removal of the tumor. In some cases, especially if the tumor is located in a hard-to-reach area, other treatments such as radiation therapy or drug therapies may be considered.

  8. Can I do anything to reduce the risk of a trichoepithelioma in my dog? While genetic factors play a role in the development of these tumors, regular veterinary examinations can help detect and treat tumors early. A healthy diet and care can generally support your dog’s health.

  9. How likely is it that a trichoepithelioma will return after removal? The likelihood of recurrence depends on the complete removal of the tumor. With complete removal, the return rate is low, but relapses can occur with incomplete removal or in the presence of multiple tumors.

  10. Should I worry if my dog has multiple cutaneous nodules? If your dog has multiple cutaneous nodules, it is important to have them examined by a veterinarian. Although trichoepitheliomas are usually benign, other skin conditions or tumors may show similar symptoms that may require different treatment.

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