Living in a country with a climate as inclement and grey as our own, it’s easy to forget that the sun can be harmful to animals, as well as humans, with horses who live out all through the summer being particularly vulnerable.

“The pigmentation in hair and skin protects against the penetration of ultraviolet light, so any non-pigmented horse or an animal with white-skinned areas is prone to sunburn damage,” says Dr Janet Littlewood MRCVS, a specialist in veterinary dermatology.

“Although the horses most at risk are those kept at permanent pasture in the summer months, it’s important not to forget that sunlight can also be damaging at other times of the year.”

The face and heels are most commonly affected because these often have non-pigmented patches and less hair coverage.

“It’s not a breed-related problem because nearly all breeds produce horses with white facial markings and legs,” explains Dr Littlewood, “but owners of animals with a thin coat should be particularly careful.”

What harm does sunburn cause?

In most horses the only harm caused by sunburn is occasional discomfort, redness and peeling. However, repeated damage can cause significant long-term problems, warns Dr Littlewood.

“It can result in thickening and scaling on the surface of the skin [keratosis], which can sometimes transform to skin cancer — squamous cell carcinoma,” she says.

“Ultraviolet light exposure also has adverse effects on skin immune mechanisms. Hence, horses with white legs tend to suffer more problems with infections, such as bacterial folliculitis and mud fever. These conditions tend to become worse and harder to manage with time.”

What can you do to prevent sunburn?

Ensuring fields have shady areas is essential, but even the most severe weather conditions won’t stop some horses grazing. There are equine sun barrier lotions available, but many owners prefer to use products made for people — high-factor water-resistant creams that are safe for children are a popular choice. But, unlike a child, it isn’t possible to bribe a horse into co-operating with ice-lollies and treats. Coloured “stick” sunblocks can be easier to apply and show up any “missed bits”.

Head and muzzle masks may provide some relief and rugs can help shield horses with more widespread sensitive areas.

What should you do if your horse is already sunburnt?

Dr Littlewood suggests that where prevention has come too late, horses should be brought inside until the problem has been resolved.

“If skin is blistered or oozing, veterinary attention should be sought. Generally, treatment is symptomatic: gentle topical bathing to remove crusts; emollient creams and antibiotics if there’s evidence of secondary infection,” she says.

All owners should monitor signs carefully, especially in an animal that has become inexplicably more sunburnt, to ensure that the horse isn’t suffering from photosensitisation. This is a condition where non- and lightly pigmented skin reacts abnormally to ultraviolet light.

“This occurs when there are reactive compounds — photosensitisers — in the horse’s circulation that cause tissue damage,” explains Dr Littlewood.

Photosensitisers can be found in some drugs, dyes and plants, including St John’s Wort and some clovers. Other plants, such as buttercups and cow parsley, contain light-reactive substances that can be absorbed directly into the muzzle during grazing.

“The prognosis for horses with primary photosensitisation is good,” says Dr Littlewood. “The underlying cause can be removed and the sores treated.

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“Photosensitisation can also occur when a horse has severe liver damage, most commonly caused by eating ragwort. When the liver isn’t functioning properly, it cannot process chlorophyll fully. This results in the presence of photosensitive phylloerythrin in the tissues. The prognosis for horses with this ‘secondary’ photosensitisation is poor, so any animal showing clinical signs of the condition should undergo thorough investigation of liver function by a vet,” she warns.

This article was first published in the 9 June 2005 issue of Horse & Hound magazine