Hello…I may have the answer you are looking for!!! I’m currently a veterinary technichian at a clinic here where I live, so I know alot about different sorts of animals. Your dad might be right…he could be having an alergic reaction to the mites, or possibly even an allergic reaction to flies or fleas. This would cause the hair to fall out, and eventually, it might cause the skin to turn a little red. I reccomend either going to a local exotic pet clinic and ask for some fly/mite/flea repellent…or try your local exotic pet store (or any store that sells stuff for horses in your area). They might have the more generic brand, but it should still do just as good. GOOD LUCK!!!.
There is a shampoo in the tack store or even online stores like stateline that is call micro tec. Its supposed to help with all sorts of skin issues. I’ve found that a plain bottle of head and shoulders works too.
Make sure all worming and shots are up to date. And if you dont see improvmets after a few baths then call the vet and ask them to take a look.
Now that its getting to be fly and tick..etc season make sure you keep him well sprayed with a good quality long lasting spray.
Call the vet and get a powder or a shampoo for mites and demite your horses ai’d do all if one has the rest will get it to.I’d do it as soon as possible as to not let it spread if it hasn’t already.