Protecting Your Horse From Sunburn And Photosensitivity


You might not think that horses can suffer from sunburn but, while it is more common in grey horses, any horse can suffer to some extent and, contrary to popular believe, sunlight can be damaging all year round – although the risk of sunburn is at its greatest during the summer months. The good news is that it can easily be prevented but problems can arise with long term repeat exposure.

Photosensitivity, on the other hand, can be mistaken for sunburn and while it often has the same symptoms its caused by too many reactive compounds (known as photosensitizers) in the horse’s tissue. In most cases though, if you remove the source of this then the problem will go away on its own.

What is sunburn?

Horses, like all animals, have pigments, known as melanin, in their skin that block the harmful ultraviolet rays from the sun. This is the same pigment that gives skin its color, but on areas of skin where there’s no color, there’s also no protection so these delicate areas are prong to ‘damage’ by the rays. This damage (or radiation as it technically is) is what we call sunburn.

While horses with gray coats, those with pinto coloring or spotted horses are more susceptible any horse with white markings (such as a blaze or stockings) can suffer from sunburn, as can horses with thin coats. As you’d probably suspect the areas most likely to suffer from sunburn are the face, tips of the ears, the heals and any white areas such as the legs but horses can actually become sunburnt anywhere on their bodies, even their back.

If you’ve ever been burnt while on vacation you’ll know how sore and painful it can be and this is no different for horses which is why, if your horse has a sunburnt back, you shouldn’t ride him until his back is completely healed.

Preventing sunburn

Sunburn can happen at any time of year but during the summer the sun is higher in the sky which is when the rays are at their strongest and therefore can do more harm. This means that you need to take extra steps to protect your horse during these months.

It goes without saying that you should provide your horse with plenty of shade, either by using trees as natural shade or with a walk-in stall, where your horse can escape from the sun but you should also try and keep him out fo the sun when it’s at its strongest. Some owners will keep their horses in during the day and then turn them out at night.

Fly or sun sheets that have been made with UV-resistant materials can block up to 70% of the harmful rays but because they’re made from meshes they can’t give your horse full protection from the sun. Masks can also offer some protection, especially ones such as Absorbine’s Fly Shield (which available on Amazon) that covers the entire face, including the ears and nose.

You can also use a high-factor water-resistant sunblock or suncream to protect exposed and vulnerable areas. As your horse continually puts his head down to graze the sunblock will rub off on the plants so you’ll need to reapply from time to time. You can use a block that’s suitable for children or if you’d prefer, some equine sunblocks are available as brightly colored sticks, this will not only help you to make sure your horse is fully covered but it’ll also allow you to see when it needs to be replaced. If you do choose to use a child-safe sunblock though make sure it doesn’t contain PABA (or para-aminobenzoic acid) because many horses are sensitive to it and it can cause painful rashes.

If you’re not keen on using sunblock then zinc oxide is a great alternative, you can buy it as a cream and it has a two-fold benefit because as well as working to protect your horse it can also be used to heal skin that has already been burnt.

Treating sunburn

Prevention is always better than cure but sometimes that just isn’t possible and if your horse is suffering from minor sunburn then you can apply something like zinc oxide, coconut oil, or an emollient cream to the affected areas. This will work to prevent infection but also help to soothe the skin and stop it itching.

If your horse’s skin has started to blister and ooze it’s better to seek medical advice, your veterinarian may advise that your horse needs a course of antibiotics.

What is photosensitivity?

Photosensitivity is severe dermatitis or skin inflammation that can be caused by digesting plants with reactive compounds (known as photosensitizers). While horses generally won’t eat these plants they can, and will, graze near them so their noses often come into contact with these photosensitizers and therefore it can make them sore too.

Primary photosensitivity

Thankfully primary photosensitivity is generally very easy to deal with because all you need to do is remove the problem plants from the pasture and then treat the sore skin. Once you’ve eradicated the plants your horse will be safe to graze again without risk of photosensitivity.

Some of the more common plants that contain photosensitisers are:

  • St. Johns Wort
  • Buckwheat
  • Buttercup
  • Cow Parsley
  • Perennial Ryegrass
  • Whiteheads
  • Ground elder
Secondary photosensitivity

Secondary photosensitivity is caused when the liver is severely damaged and can’t process chlorophyll properly. This means that the horse can’t dispose of the phylloerythrin properly (its normally removed via the horse’s droppings) and therefore there’s too much of it in the tissue. Phylloerythrin is accumulative and highly photosensitive so when the skin is exposed to ultraviolet rays it erupts and blisters.

The prognosis for secondary photosensitivity isn’t so good because by the time the liver is damaged enough to show the symptoms through the skin the chances of making a full recovery are much less. If you suspect your horse is suffering from this then it’s vitally important you speak to your veterinarian immediately, he’ll also be able to check the other horses because if your horse has eaten something toxic then its highly likely other horses have too.

Not all horses will show visible signs of secondary photosensitivity (around 25% will) so its important to recognize the first signs of liver damage. Most horses will lose body condition as well as their appetite but lethargy is also a symptom. Horses can become constipated or suffer diarrhea but any yellowing of the skin (known as jaundice) is a tell-tell sign of liver damage and is most visible around the eyes and inside the mouth.

One of the main causes of secondary photosensitivity is the digestion of plants containing pyrrolizidine alkaloids (PA) which are highly toxic, especially to the liver. These plants will often remain toxic even after being picked and dried but thankfully they taste very bitter. This taste means that horses won’t choose to eat them unless of course they’re really hungry and don’t have access to proper forage or other food. The most common plants to contain pyrrolizidine alkaloids are:

  • Ragwort
  • Alsike clover
  • Red clover
  • Tarweed
  • Purple viper’s bugloss
  • Houndstongue
  • Rattlepod
  • Gromwell

You can find a more definitive list on Wikipedia

Preventing photosensitivity

Both primary and secondary photosensitivity can easily be prevented by making sure that all pastures and grazing areas are free from all plants that contain photosensitizers but all, and more importantly, all plants containing pyrrolizidine alkaloids. 

With regards to toxic plants though it’s important to remember that they can remain toxic for many months (if not years) after so make sure your hay supply isn’t contaminated with these plants. You can do this by buying from a reputable producer or, if you produce the hay yourself, making sure there are no toxic plants in the fields.

Treating photosensitivity

If your horse is suffering from primary photosensitivity then it can be treated in much the same way as sunburn can, although it may also be advisable to bring your horse in until he’s better.

Secondary photosensitivity, on the other hand, requires prompt veterinarian intervention so while you can treat the visible signs such as blistering skin you shouldn’t delay calling the veterinarian.

Further reading

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