The insect repellent is on an oily base without water, so it does not evaporate.
It resists the sweat of the horse. It is effective against flies and mosquitoes but also against "creepers" like ticks, flat flies, horseflies, fleas, lice.
It will resist under a little rain, but if you shower your horse it will have to recover.
Depending on the horses and the protein level of their sweat, it will hold from 12 to 48H.
It isn't aggressive on sensitive skin and/or dermatitis.