What is this photosensitivity that I hear about?  Isn’t it the same as sunburn?

While they look alike at first, photosensitivity has a different cause - an internal cause.  Sunburn is caused by just the sun on skin, photosensitivity can be primary or secondary depending on the cause.  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 react with UV light 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.  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.



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


Secondary photosensitivity 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 phylloerythin and the skin can start to react. 


It’s important to know that photosensitivity is painful and can take weeks or longer to heal.  Work alongside your Veterinarian to create a treatment plan.  Exposure to UV light causes the skin reactions, so it’s critical that your horse remain out of direct sunlight.  Many photosensitive horses are visibly agitated and uncomfortable when in the sun.  Evening turn out with days spent inside are the best opportunity for your horse to heal and recover.  



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


Don’t peel any crust, don’t pick any scabs, keep the sores clean and dry.  Minimize the flies that can get to your horse.  Fans, fly sprays, sheets, fly boots, and fly masks with noses all help.  There is great risk of secondary infection, and in some cases your Veterinarian will need to prescribe medications to help healing. 


It’s also wise for your horse to be evaluated for liver problems to determine if the photosensitivity is primary or secondary.  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 then help heal his photosensitive sores.  



Photosensitivity can start in your horse's favorite place - the pasture!


How have you helped the photosensitive horse?