I cover my horses noses with Wal Mart's brand of diaper rash cream. When I'm done, you can't see any of the skin :P
The reason it works is the 10% zinc oxide it contains, which is the same as the more expensive Desitin brand.
A couple of my horses have pink areas on their upper and lower lips. I cover those areas too. They may lick their chops and get some off but it hasn't hurt anyone.
You can also buy 20% pure zinc oxide at WalMart. It comes in a red & white box and is back in the pharmacy area. I can't remember if I bought it in the foot care area or the baby care area
It also stays on good, but I mix it with diaper rash cream because there's something in the diaper rash cream that makes it a lot more water repellant.
I have a friend whose APHA is pink-skinned on his entire face. She was using a high SPF sunscreen and was putting it on as thick as I put the diaper rash cream on.
She ended up having to have the vet come because the horse's pores got blocked from the sunscreen. The vet told her to use diaper rash cream so that wouldn't happen.
I am not saying that is going to happen to every horse; just wanted to post it as an FYI :)