I live in Texas and we are having the hottest summer on record and thee same thing is happening to my horse!! Around his eyes and ears mostly..I'm pretty positive its the extreme heat and sweat because it has never happened to him before, he is 12.
Could be sweet itch, I have seen many horses and ponies which loose hair round their eyes and ears with this. I use sweet relief which is a lotion used for sweet itch and other irritating skin conditions. Try this web site sweetitch.net it has some really good fly spray too. Good luck
One of the family's mare's always sheds around her eyes in the summer. Its hot and humid here too! It doesnt come out in chunks, it doesnt have any irritation or color change in her skin, its just bald!