Where am I and what am I doing in this handbasket?
I just call mine "fungus face" or "scarface" depending on my mood...
This summer the face crud is worse than normal, defeating even his regular rinse/bathing, so I decided a little higher test treatment was in order: good ol' coal tar shampoo, picked up the Tar-Jay knock off of Neutragena and it's done a nice job on the head. Still working hard in the hind cannon keratosis, but it's coming along.
This year has been so bad, my other (bay) horse who has it on his hind legs year round and adds his face for the summer ... he is even battling it down his back. Sigh...
Keep the mask and the horse's face EXTREMELY clean. Also have a few different styles and shapes of fly masks, and rotate them. I have 4 fly masks for my mare, that I rotate. I also brush/curry the crap out of the fleece lining on her masks every day to get all the dirt out, and to "fluff" the fleece. I find if I let the fleece get flattened down, she gets rubs very quickly.
Tell a Gelding. Ask a Stallion. Discuss it with a Mare... Pray if it's a Pony!
I rinse off his face every day and rub with either my bare hands or one of those scrubby cloth bath gloves made for people (I.e., pretty gentle), then towel dry. I sometimes put some aloe cream on the really bad spots. The fact that he stands and allows his turnout buddy to bite him in the face all the time really doesn't help the cause, though!