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There are many different problems that can affect a horse's skin. These issues can range from very simple allergies and dermatitis to parasites and even tumors such as sarcoids and melanomas. When dealing with a skin condition in horses, it is important to understand the root cause of the issue in order to treat it effectively.

What Skin Conditions Can Horses Get?

Skin conditions in the horse can be broken down into several categories:

Dermatitis

  • Scratches/pastern dermatitis/greasy heel: These are some of the most common conditions affecting horses. Damp conditions and skin irritation lead to bacterial overgrowth, which causes redness, flaking, and crusting of the skin typically on the legs and pasterns.

  • Thrush: This is another overgrowth of bacteria and fungi, this time in and around the frog of the hoof. Thrush leads to bad odor and changes in the frog, but rarely lameness.

  • Rain rot: Secondary to a damp coat (whether that is from rain or being left damp under a blanket after sweating or being given a bath), bacteria and fungus multiply to cause skin irritation.

  • Cellulitis: A very small wound or other opening in the skin (including from scratches or pastern dermatitis) can allow bacteria to get into tissue under the skin. Once under the skin, the bacteria spreads and causes extensive swelling and edema. If left untreated, this infection can spread to the lymph nodes and a horse can become systemically ill.

  • Dermatophytosis (ringworm): Despite the name, ringworm is caused by a fungus found in soil. It causes loss of hair in very characteristic circles. This disease can be spread to humans.

  • Seborrheic dermatitis: This form of dermatitis is characterized by a greasy hair coat and flaking. It can have a combination of underlying causes, including allergies and bacterial/fungal infections.

Viral

  • Papillomatosis (warts): This virus causes warts to appear primarily on the noses of young horses whose immune systems are not as strong as adult horses. Warts are caused by contact with other young horses that have them and typically disappear over time.

  • Aural plaques: Another papilloma virus-induced condition in horses, aural plaques are raised papules that form on the inside of the ear. They are unsightly to look at but are otherwise benign.

Parasitic

  • Mange: There are various mites that cause the condition called mange. It can cause itchiness and hair loss. Some of these mites can be spread to humans.

  • Lice: Lice infestations are uncommon in horses but cause noticeable itchiness. Lice are also communicable to people.

Atopic/Allergic

  • Hives: Just like people, horses can have allergic reactions to things in the environment including pollens, detergents/chemicals on riding equipment, or even components of their own sweat. Hives are not always associated with itchiness but can be bothersome.

  • Sweet itch/insect hypersensitivity: These conditions are exaggerated reactions to insect bites that can result in welts, hair loss, itchiness, and other symptoms.

  • Eosinophilic granulomas: These are small nodules that typically form along the horse’s back and are made up of collections of allergy-driven immune cells. They are often seen as a response to a sensitivity to detergents or chemicals in saddle pads or other riding gear.

Neoplastic (Tumors)

  • Sarcoids: These tumors can vary greatly in appearance. Although they are not malignant tumors that will invade other organ systems, they can become very large and locally invasive, especially when aggravated by attempted surgical removal. There are some newer treatment options that are showing some success in decreasing the size of sarcoids.

  • Melanoma: These tumors are most often found in gray horses. They can form anywhere on the horse but are commonly seen around the rectum and tail head.

  • Squamous cell carcinoma (SCC): This cancer is most often found in and around the eyes and on the penis in horses. It can become malignant if not addressed at an early stage. Certain breeds such as Haflingers and Belgians are predisposed to SCC.

Toxin/Liver injury

  • Photosensitization: This condition results in horses becoming excessively sensitive to sunlight, especially on areas with white hair. They will often lose their hair in these areas and develop severe sunburns. There are two pathways that can cause photosensitization—ingestion of toxins (St. John’s wort and others), and liver injury.

References

Cummings School. What You Need to Know: Squamous Cell Carcinoma in Horses. News Center at Cummings School of Veterinary Medicine at Tufts University. 2018.

         Pfeifer, Mallory. Photosensitization: Causes and Testing Options. Texas A&M Veterinary Medical Diagnostic Laboratory. 2021.

Featured Image: iStock.com/fotocelia

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