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By Kristen Slater, DVM

Skin Problems - Jul 25th, 12

The skin is the largest organ of the body. It serves to protect internal structures from a variety of environmental stimuli. In the summer months this is an especially vital organ for fending off a barrage of flies and the relenting summer sun. 

Like humans, horses are susceptible to sunburn, especially on the non-pigmented pink-skinned areas of the body. Sunburn is most frequently seen around the eyes and on the muzzle of pale or white-faced horses. For this reason many of the breeds that most frequently suffer from sunburn include Paints, Pintos, and Appaloosas, as well as many cremellos and other horses with pale coat colors. 

The skin condition photosensitization (a sensitivity to sun exposure) is different from sunburn in that it often affects both pigmented and nonpigmented areas of the body. Some photosensitizing agents include, but are not limited to, St. John’s wart, ragwort, buckwheat, perennial ryegrass, sulfa antibiotics, and tetracycline. Clover (mostly alsike and red) as well as alfalfa are linked to secondary photosensitivity due to liver damage, which can occur from heavy ingestion of these plants. Photosensitization also can secondarily result from liver damage due to bacterial, viral, or fungal infections and even liver cancers. 

Skin lesions, primarily around the eyes and nostrils, are the first signs owners often see when sunburn or photosensitization occurs. Affected skin often peels or appears scaly and redder than surrounding pale skin (areas devoid of pigmentation). In severe cases horses might even develop blisters and leak serum (clear to yellowish fluid) from the damaged skin, just as with a deep sunburn in humans. 

Most frequently I see sunburn when an owner complains that his or her horse is suddenly head shy. Anyone who has ever suffered the painful effects of sunburn should be able to understand easily why a horse suffering one on his face would be reluctant to wear a halter or bridle. 

In addition to the painful aspect of sunburn, there are long-term consequences to consider in horses prone to recurrent sunburn. One of the most significant of these issues is an increased likelihood of developing squamous cell carcinoma (a common cancer). 

There are many options available to help reduce the likelihood of sunburn in the horse. Just as in humans, the best advice is to avoid sun exposure when possible. This is often achieved by stabling the horse during the day and allowing him to graze from dusk to dawn. This way, he is still able to get some sun, but not during peak exposure to ultraviolet (UV) rays. Another preventive measure many people have employed is the use of sunscreen. There are few options as far as equine-specific sunscreens, although many fly spray products do carry some degree of UV protection. Many people use human products, such as children’s sunscreens, on their horses, and color-changing preparations are available so owners can see that areas are appropriately covered. However, in my experience, many people initiate sunscreen applications too late (i.e., after the horse has already suffered some ill effects of sunburn), and horses become resistant to application of the product. Furthermore, sunscreen needs to be reapplied, just as on people, to be fully effective. Another preventive option is the use of a full-face fly mask. Many of these come with UV protection and cover the entire face, including the ears. For horses with large areas of white over the back and trunk, however, it might be necessary to use a full-body fly sheet. 

If a horse sustains even a mild level of sunburn before these preventive measures are implemented, he might act head shy or unusually resistant to saddling (for those with sunburn over the back). Unfortunately, sunburn recovery in the horse can take months, so be patient and understand the horse is just showing his discomfort the only way he can. 

About the Author: Kristen Slater, DVM, practices equine veterinary medicine at Kasper & Rigby Veterinary Associates, in Magnolia, Texas. Her veterinary interests include preventive medicine, reproduction, and sports rehabilitation and conditioning. 

Article provided courtesy of AAEP Media Partner, The Horse.