Ask the Vet Video on Causes of Allergic Reactions in Horses

SARAH: "How do you tell if a horse has an allergy to fly spray or some other product? I've heard of horses having reactions to citronella, but what are some other common ingredients that horses may have a reaction to?"

All right, so we got two questions. How do you tell if your horse is having a reaction? And what are some common ingredients that might cause it?

DR LYDIA GRAY: I better start with the common ingredients because if I get talking about the other, then I may forget it. So here's a list that I found. Neoprene is in some splint boots or girths. Some horses just don't do well with neoprene. Wool and the lanolin in the wool, but there's also lanolin in products, like some shampoos and stuff have lanolin. Rubber or latex like you might find wrapped on a bit or something. So those are some common products that horses can have a local reaction to.

And then, her first question is, how do you tell? When you're having a reaction to something that you contacted-- so contact dermatitis-- it's in the area right where you touched it. So if you're going to have a sensitivity to bedding, then it's where you laid in bedding. So a horse might get up and have a little shavings suck on them and then have bumps too right there. If it's a neoprene or something, then right where you put the neoprene or the wool might be in the saddle area. If there's something on the bridle.

So if she's talking about fly spray, if you sprayed it in an area-- a certain area-- it would be exactly where that spray landed. And then the signs would be the hives, the bumps, itching, maybe some dryness or hair loss. But what you do is you don't put something on a horse on its entire body the first time. You do a patch test or a spot test. And you just pick a little area, you apply the product, and then you wait 24 to 48 hours.

If your horse is going to have a local reaction, it will happen in that time frame. If not, chances are, he's OK with it and you can use it everywhere you need to. So did I answer that?

SARAH: I think that answers both of the questions. Do you now-- and this is a separate but kind of related question-- if horses are, like-- and this might not even be true for people. But I've heard that if the first time you're exposed to something, you might not have an allergic reaction. But then subsequent exposure could cause it. Do we see that same sort of thing in horses?

DR LYDIA GRAY: Yes. But allergies are different. So you can have a contact dermatitis that is not allergic. And you can have hives that are not because of allergies that are just because of--

SARAH: --irritation.

DR LYDIA GRAY: Yeah. So a local skin response, the local ones probably aren't systemic immune-related. And so that phenomena that you're describing of the first time, you get a freebie. And the second time, well, that's not going to happen.

SARAH: Because that's more related to allergies. It's not related specifically.

DR LYDIA GRAY: Now, if the horse has a true allergy to a substance, then yes, it takes exposure the first time and then the next time, they get worse. So that can happen too. And that's why allergies and hives due to allergies are so challenging to figure out because you don't know what the things were that could have caused this because it's systemic. Like contact ones, the reaction is right there where you put it.

SARAH: It's localized.

DR LYDIA GRAY: Right. And systemic ones, the true allergies are like whole body. But it could have been something that they touched or inhaled or ate. And so then, you're back to that process of elimination.

SARAH: Yeah.

DR LYDIA GRAY: Ugh.

SARAH: But what you can do to help yourself out in a situation like that is something my good friend Dr. Gray always does, which is journal what you're doing with your horse. Because if you write in your journal that you started your horse on a new feed, or you introduced a new product-- whether it's a topical product or a piece of equipment that has wool in it that you've never used before-- and then a couple days later, you notice that something's happening, those might be trends you could share with your veterinarian to help you in that overwhelming process of elimination of all of the things that could be causing what's going on.