WE are all aware of the importance of protecting our skin from too much sunshine. Like us, our horses can suffer from sunburn due to overexposure to sunlight. They are particularly vulnerable around their muzzle, eyes and any areas of white coat and thin hair. Sun protection can be provided by using fly masks and fly rugs, and the application of sun cream to the exposed of skin. Shelter or shade is preferable in hot weather so a field shelter or well-ventilated stable will give your horse protection during peak daylight hours.

As well as causing sunburn, UV light plays a part in some other ailments so during the summer months we can see an increase in other skin conditions. Although some of these can have a similar appearance, they may have other underlying factors that require investigation or different treatments.

Photosensitisation is a more severe skin inflammation than sunburn. Areas of oozing and swelling tend to occur on the areas of the skin most exposed to the sun including the outside of the lower legs and around the face, but any white area with pink skin underneath can be affected. Photosensitisation occurs when certain molecules are present in the skin. Primary photosensitisation is caused directly by eating certain plants (e.g. St John’s Wort) whereas secondary photosensitisation occurs due to liver damage as the liver can no longer break down products from plants properly. Substances from these plants circulate through the body and reach the skin where they react with UV light causing a photosensitisation reaction. Differentiating between primary and secondary disease may require blood tests to assess the liver. Treatment is either by removal of the agent or treating the liver disease.

Leukocytoclastic vasculitis is another condition influenced by UV light, affecting the white and unpigmented areas on horses’ limbs. It is a painful immune-mediated condition found in adult horses but is not well understood. Signs are seen in the summer and as both the outside and inside of the pasterns are affected this can help to differentiate it from photosensitisation. The lesions appear reddened, crusting and oozing and the legs may swell, all of which can lead to lameness. When this condition is suspected or confirmed, the affected areas require protection from UV light by stabling the horse and bandaging the limbs. Steroids may also be prescribed as an immunosuppressant to control the condition, and treatment to control any secondary bacterial or fungal infection to the lesion may also be required.Buttercups, the common weed often found in pastures, are an irritant to the skin of the horse, causing a contact dermatitis resulting in blistering to the skin particularly on the pink areas of the muzzle and the lower legs as they come into contact with buttercups when grazing. In addition to skin irritation this weed can also cause irritation to the inside of the mouth, so it is best to try and reduce the quantity of buttercups on horse pasture.