Pyranha made BOTH my horses break out in massive welts that blistered and hurt to the touch, lasted about a week because the stuff was too greasy to wash off. You could see the streaks of swelling in the pattern that I sprayed them. Including their poor sad undersides!
That taught me to try Everything on just a small area before using alot of it!
One of my horses has sensitive skin, so I would assume something from her, but NOT my pony, he's very thick skinned. Pyrahna is Awful Don't use it!
I use Repel X but it's not strong enough for end of summer season. This year has just been awful, so I use swat on her worst spots and mix Clac and Repel X concentrates and dilute.