Have you ever wondered what is in your fly sprays? Here we reveal what is in some of the most commonly used fly sprays, how high the concentration is and if it could do you or your horse any harm!

PMD/ p,mentane3-8 diol/ Citriodiol/ Citrepel/ – Repellent
Lincoln Fly Stoppa 0.8%*, Fly Repel 1%, Naf-off 1%, Barrier Super Plus 1%, Carr Day and Martin,

PMD is a natural repellent chemical extracted from the leaves of the lemon eucalyptus tree. As you can imagine it has a lemon scent rather more like menthol then the common citronella. Citriodiol and Citrepel are trademarked compounds that contain PMD at 64% and 40% respectively.

Much research has been done into PMD and many health organisations deem it to be as effective as synthetic compounds such as DEET when used in high concentrations. Many fly repellent manufacturers use it but often in very low concentrations as a scent rather than in higher concentrations where it would prove more effective.

Like menthol it can cause a ‘tingling’ sensation on the skin which can be slightly irritant to more sensitive types, so is best used with caution with patch tests performed before wider application.

DEET – Repellent
Power Phaser 5.51%*, Lincoln Fly Stoppa 10%*, NAF Power 19.4%

N,N-Diethyl-meta-toluamide or DEET was developed by the US army for use in jungle warfare in 1946 and has been commonly used ever since.

Consumer tests in humans have suggested that DEET provides a good protection against mosquitos, around 3-6 hours at 20-34%. Although mosquitos are not a prime concern with horses.

DEET is a powerful solvent which is known to dissolve leather (and hence skin) and synthetics over time, making it unwise to use on or around any kind of tack. DEET has been known to cause seizures in a small percentage of human users and many health organisations have banned it’s use at higher concentrations due to safety concerns and findings that it can be a neurotoxin in mammals.

Saltidin® – Repellent (also known as Icaridin or Picaridin, formerly Bayrepel)
Red Zone Super: 20%*, Boehringer Ingleheim Centraura : undisclosed concentration

The current repellent ingredient of choice for malaria prevention from the World Health Organisation. Saltidin has been reported to be as effective as DEET without the associated irritation and safety concerns. According to the World Health Organisation, Saltidin “demonstrates excellent repellent properties comparable to, and often superior to, those of the standard DEET.”

Saltidin is not used in many repellents as it is up to 5 times more expensive than DEET for manufacturers to purchase. Although some manufacturers absorb this into their company structure making their prices comparable to those containing DEET.

Citronella – Repellent
A number of ‘summer’ and ‘horse’ sprays at undisclosed concentrations.

Citronella is a natural oil that is now banned as a repellent ingredient in horse products but is used in some that have been re-branded as ‘horse’ or ‘summer’ sprays.

Citronella oil’s mosquito repellency has also been verified by research, including effectiveness in repelling but requires reapplication after 30 to 60 minutes and needs to be at high concentrations. However midge and horsefly effectiveness seems to remain unproven.

Ethyl Butacetylaminopropionate or IR3535® – Repellent
Power Phaser : 4.9%*, Effol Horse Fly Blocker: 10%

The U.S. Centers for Disease Control issued a statement in May 2008 recommending equally DEET, picaridin, oil of lemon eucalyptus (used to make Citriodiol/ PMD etc) and IR3535 for skin application in malarial areas.

Considerable testing has been done to assess the harmfulness of this active and thus far it seems very safe even at concentrations of up to 30%. IR3535 does seem to have a good safety profile and good chemical stability.

In a 20% spray Merck™ (the manufacturer) lists IR3535 as having high efficacy against bees, mosquitos, ticks and lice but only a medium efficacy against stable (horse) flies and deer flies (tabanids). It does not list the relative efficacy on midges.

Cypermethrins, permethrins – Insecticides
Tritec : 0.15%*, Coopers

These ‘pyrethroids’ act as neurotoxins to insects. Cypermethrin is a synthetic repellent ingredient used as an insecticides in large-scale commercial agricultural applications as well as in consumer products for domestic purposes. It is a neurotoxin to insects but is only absorbed when then bite a treated host or the ingredient is fresh on the skin. In most cases the insect is only effected once the horse has been bitten. Most pyrethoroids are broken down by sunlight, so may not last long on a horses coat in the summer!

Excessive human exposure can cause nausea, headache, muscle weakness, salivation, shortness of breath and seizures. Permethrin is also listed as a likely human carcinogen by the USEPA and is incredibly toxic to cats!

Benzyl Benzoate – Insecticide

‘Benz-benz’ is a creamy substance often used as a sweet itch treatment. It is effective at killing mites and other small insects. Due to its skin irritant effect it is ill advised to use it on broken or hairless skin or at full concentration.

Different Actions:  

  • Different spray ingredients can work in different ways, here is what those actions mean:
  • Repellent: An ingredient with a repellent effect usually works by confusing the insects sense of smell and masking the treated animal or by creating an unpleasant smell that deters the insects. Hence insects tend not to even land on the host.
  • Anti-Biteant: Causes the treated animal to have a layer on its skin/ hair that deters insects from biting – they will likely still land, but the horse effectively tastes nasty!
  • Insecticide: Kills insects, unfortunately in many cases it kills them when they have contact with the blood rather than the skin, so they will tend to land, bite and then die.

In Conclusion:

Choose what repellent you use carefully and try and read beneath the marketing hype and ‘traditional’ ideas. Modern active ingredients would not have been developed if the ones on the market were ideal, especially since they often cost more to manufacture. Products containing a high (over 10%) concentration of IR3535 or Saltidin/ Icaridin/ Picaridin offer the best safety and efficacy, but you can expect them to be more expensive as a result of the use of these more advanced and hence more expensive ingredients.

By Sam Austin

Head Formulator at Red Horse Products LTD