The Curly horse with it's unusual coat, has proven to be hypoallergenic to many people allergic to other breeds of horses. The Curly Horse coat is suspected to have different or less proteins that make up the hair, skin, and oils, in comparison to normal horses. These proteins are different enough that many people with allergies do not react to them. Not every person is free from reactions to Curly Horses. Some people react to particular Curly Horses, however most have been able to find a Curly Horse that was not a problem. Often an "extreme" Curly (a Curly with a very curly coat and very little mane and tail hair) is the solution.
"Smooth coated" Curlies (Curlies that show no curl in their coat, manes, and tails, but have Curly bloodlines) are also found to be hypoallergenic for a lot of people allergic to regular horses. There are also Curly Horses that are not "extremes" or "smooth coats" , and have varying degrees of curls, also varying manes and tails. One of our friends who is highly allergic to horses, but has found the Curly Horse to be fine, has found 50% of the time crossbred curlies (especially those with 1/2 Curly blood) to be hypoallergenic for him. Each person is different, if you are an allergy sufferer, you should test the horse you may be purchasing by either an in-person visit, or at least by asking for some of the hair to be sent to you.