UV Photosensitivity in Horses.


Photosensitivity in horses is a painful condition where the sun’s UV rays create sores, burns, blisters, and more on a horse. OUCH.


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  • While photosensitivity can resemble sunburn or scratches, photosensitivity has a different cause – an internal cause.


  • Sunburn is caused by just the sun on the skin, photosensitivity can be primary or secondary depending on the cause.


  • UV photosensitivity also contributes to vasculitis, which is inflammation of the blood vessels. Also OUCH. Photosensitivity is also part of the larger equine pastern dermatitis (EPD) umbrella, which is a complicated syndrome, not a specific diagnosis, and has a multitude of possible causes. You will usually some of the following: scabs, inflammation of the skin, lesions or sores, blisters, lameness (!!), hair loss, redness of the skin, crusty hair, blisters, lizard-like skin, itchiness, and even oozing and thickening of the skin. None of this is comfortable for your horse. For more on EPD, this will help, photos and all.


Primary photosensitivity is caused by plants that act on your horse from the inside out.


  • When your horse eats certain plants or medications, that plant is broken down and photodynamic compounds are released into your horse.


  • These compounds inside your horse react with UV light outside your horse and cause painful redness, blisters, scaly skin, scabs, open sores, and swelling. This occurs on pink skin, so chrome legs, noses and blazes and other areas with true white hair are affected. If you have a paint or pinto, the skin on those large areas of white is also affected.


  • Plants such as perennial rye, smartweed, burr trefoil, buckwheat, and St. John’s wort are all causes of primary photosensitivity.


  • Medications such as sulfonamides, tetracycline, and phenothiazine are also causes, to name a few. This may mean that your horse becomes photosensitive temporarily. Anytime a medication is given, you should ask your Vet if it’s known to be a cause of UV photosensitivity.



These chrome legs are prime areas for photosensitive sores to erupt. It might even look like scratches.


Secondary UV photosensitivity in horses is caused by liver damage.


  • When your horse eats certain plants, like buttercup, lantana, bermuda, kale, tarweed, and certain types of clover (there are many other plants as well) his liver may become damaged.


  • A damaged liver is unable to remove the photodynamic compound phylloerythrin from your horse’s diet, and the skin can start to react, showing up as painful sores on pink skin.



sox for horses on a horse leg standing in grass

These Silver Whinny’s by Sox for Horses can help with all sorts of skin ailments


Photosensitivity is painful and can take weeks or longer to heal.


  • Work alongside your veterinarian to create a treatment plan for the photosensitive horse. You will need to address any liver issues, any pasture contaminants, and find a way to keep the UV rays away from your horse’s pink skin. You and your vet also need to create the long-term plan so flare up’s don’t return.


  • Exposure to UV light causes skin reactions, so it’s critical that your horse remains out of direct sunlight. Many photosensitive horses are visibly agitated and uncomfortable when in the sun, they may even appear to be actively trying to escape the sun’s rays.


  • Evening and overnight turn out with days spent inside are the best opportunity for your horse to heal and recover. This may not always be possible, so you will need to find ways to physically cover your horse up.


  • Physically blocking the UV rays from reaching your horse’s white skin is a must. Sox for horses can help your horse’s legs in that department. The double layer of magic silver fabric does two things – help block the UV rays AND help heal the wounds on the legs. Actually, more than two things – these horse socks also keep flies away, help with stomping, and keep skin issues clean and dry.


horse pink nose doing flehmen response

Noses, blazes, and other true white hairs with pink skin underneath is where you will find the blisters, crusty sores, and painful peeling.


What’s the plan to heal the sores the UV photosensitivity causes?


  • It’s fairly easy – Don’t peel any crust, don’t pick any scabs, keep the sores clean and dry if your horse is photosensitive. This helps prevent further secondary infections from taking hold.


  • Minimize the flies that can get to your horse. Fans, fly sprays, sheets, horse socks, and fly masks with noses all help. Flies are a huge contributor to secondary infections! Time for fly control measures that essentially declare war on these jerks.


  • There is a great risk of secondary infection, and in some cases, your Veterinarian will need to prescribe medications to help healing. These could be oral meds, or topical meds.


Have your horse evaluated for liver problems


  • Liver damage is not something you want to ignore in your horse, and this will help your Veterinarian come up with a treatment plan that does more than help heal his photosensitive sores.


gray horse with fly mask grazing on a hill

Photosensitivity can start in your horse’s favorite place – the pasture!


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Stock up here for your horse supplies! As an Amazon Associate, I earn from qualifying purchases, but it’s ZERO extra cents to you.  You can also visit my Amazon storefront here:  PEG storefront.

Whinny Wellies from Sox For Horses

Tough, weather-resistant covering for wraps and bandaging.

Silver Bells - Sox For Horses

For hoof protection when equine pastern dermatitis is a risk.

Fly Whisk

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Farnam Equi-Spot, Horse Fly and Tick Control, 12-Week Supply for One Horse
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This spot-on product kills and repels ticks and helps with mosquito control.

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Cashel Quiet Ride Horse Fly Mask with Long Nose and Ears

This style is great for riding!

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If you need an extra layer of protection for your horse’s legs and face, I suggest these. As an Amazon Associate, I earn from qualifying purchases, which are at no additional cost to you. I greatly appreciate your support!