By Tim John, DVM

Continued from What’s in My Horse’s Fly Spray, Part 1

In the previous post, we discussed fly sprays that contain pyrethroids as the active ingredient. Now, let’s look at those sprays with essential oils as the active ingredient.

As discussed, horse fly sprays can be broken down into two broad categories: those with pyrethroids and those with essential oils. This differentiation corresponds to how the EPA looks at fly sprays or, as the EPA likes to call them, insect repellent products.

In the United States, the EPA divides products into two types: registered and unregistered.

Pyrethroids all fall into the registered category. To become registered, products must submit to and undergo a long process to show efficacy and safety. When they pass, there are explicit instructions on how the product is to be used.

Unregistered products fall into a bit of a loophole. They contain ingredients from an approved list of minimal-risk pesticides and are for the most part essential oils. This list was developed because the EPA feels that these products are generally safe.

Essential oils are nature’s own defense mechanism. They are produced by plants to guard against would-be predators, in order to stop attacks and repel invaders.

These volatile oils are highly effective and literally save the plant’s life. So it makes sense to utilize nature’s best weapons for ourselves, right?

Unfortunately, it is not always so easy to borrow these ideas without running into potential problems. In the case of fly sprays, those issues include:

• efficacy,
• duration of effect, and
• safety.

Essential oils are by their nature very volatile. When they are extracted from plants, the remaining portion tends to evaporate very quickly at animal body temperatures.

Probably the best-known essential oil is Citronella. Undiluted, it may repel flying insects for two hours.

Most common fly spray products contain between 5% to 15% concentrations, and some studies suggest they may only last 20 to 30 minutes. While higher concentrations of these oils work best, they are also the most likely to cause irritation to the eyes or skin. For example, peppermint oil is a known contact skin sensitizer in humans.

As it is expensive to run good scientific studies on these compounds, there is very little hard data available in regards to efficacy or duration of action for essential oil compounds. However, most herbalists agree that mixing different oils together can enhance their effect while minimizing the potential for an adverse reaction.

Most horse owners find that the combination of questionable efficacy and the need to frequently reapply these sprays leads to a very disappointing overall experience when using these products. If they are going to be successful, we need to keep in mind their limitations. Fly sprays with essential oils as the active ingredients are probably best considered when there is light insect activity and no increased exertion by the horse (activity = heat = increased evaporation of product from the horse).

So what are we supposed to do?

Certainly you want to protect your equine friend from pests, and there are many (many!) options out there for you to consider. I believe that knowledge is power in this case. Be a label reader. Be aware of what you’re using on your horse, and in turn yourself and potentially your kids. Ask trusted veterinary professionals and horse friends for input on products. Then do your own research so you can find a product that not only works well for your horse, but is also safe for you, your family, your equine friend and the environment.