Halter rubs, blanket rubs, any kind of rubs! They are absolutely anyone for the horse owner and can be painful for the horse.
Rubs are when friction from a halter/fly mask/blanket/etc irritates the horse's skin. Hair often gets rubbed off, leaving sensitive skin to be rubbed further. This can cause painful open sores that will only get worse if they are not treated accordingly.
I will cover different ways to prevent, protect, and heal the rubs.
1 - Vitamin E cream
This cream promotes new hair growth, if there is no open sore. If there an open wound, use an ointment as you would any other minor wound. Once it has healed, apply the cream thoroughly. Cover the cream (if at all possible) with a fly mask, bandage, etc. so that your horse is less likely to rub it off.
2 - Petroleum jelly
This useful the prevention of halter/fly mask rubs on the face/head or other small areas. On the of fly masks, try using a nylon/lycra blend fly mask. They are much less likely to cause rubs (I'm talking from experience here - this exact thing happened to my pony) than the masks made of more traditional materials. Having multiple different styles of fly masks can be useful as well to figure out which one works best for your horse (or just in case one needs to be cleaned or repaired).
3 - Shoulder Guards
These can also be known as sleezies or jammies. They are often a stretchy and form fitting 80% nylon/20% lycra blend that covers that chest, shoulders, and withers. Wearing a shoulder guard will prevent rubs from progressing, or from starting at all.
Hope this was helpful.