By Paula McGovern, Founder of Wizard & Grace Wellbeing
Anyone who has tried to enjoy a summer evening outdoors in Ireland knows the problem. The light is perfect, the temperature is finally right, you've lit a candle and sat down - and then the flies arrive.
I've been experimenting with essential oils as a natural deterrent for flies and midges for a few years now. Not as a replacement for a chemical repellent, but as a genuinely effective way to make outdoor evenings more enjoyable and reduce the flies coming into my home in summer.
Here's what I've found actually works, what the science says, and how to use it practically.
Why Essential Oils Deter Insects
Flies and other insects navigate primarily through scent. Their antennae contain hundreds of olfactory receptors that detect food sources, breeding sites, and potential dangers. Certain plant-derived aromatic compounds disrupt this sensory system - either by masking the odours that attract insects or by directly overwhelming their olfactory receptors.
This isn't folk wisdom. A peer-reviewed study published in the Journal of Vector Ecology found that essential oils containing high concentrations of monoterpenes - particularly linalool, citral, and menthol - repelled over 75% of flies when used at a 5% concentration, with protective effects lasting six to eight hours.
The key compounds to look for are:
Menthol - found in peppermint oil. Strong, overwhelming scent that flies find deeply unpleasant.
Citral and geraniol - found in lemongrass. Naturally occurring compounds that disrupt insect navigation.
Eucalyptol - found in eucalyptus oil. Disrupts flies' ability to detect scent, leaving them confused and deterred.
Linalool - found in lavender. Has demonstrated repellent effects against flies and other insects by disrupting their nervous system signalling.
The Essential Oils That Actually Work to deter Flies
Peppermint - the most effective
Peppermint is consistently the most researched and most effective essential oil for fly deterrence. Its menthol content is deeply unpleasant to flies - research has shown peppermint oil can provide significant protection against flies and mosquitoes for up to several hours when applied or diffused.
The scent is strong enough to overpower the odours that attract flies to a space in the first place. It's particularly effective indoors near windows, bins, and food preparation areas, and outdoors when diffused or applied to a candle.
Our Flow candle and Focus Pulse Point Oil contains peppermint as its primary oil = and I've found it genuinely useful lit on the table during outdoor summer evenings.
Lemongrass - the outdoor specialist
Lemongrass contains citral and geraniol - two compounds that appear in commercial natural insect repellents because they work. It's particularly effective against flies and mosquitoes outdoors, where its bright citrus scent disperses well in open air.
Research confirms lemongrass as one of the most effective plant-based fly deterrents available. It's also a much more pleasant scent outdoors than citronella - which tends to be the first thing people reach for but has a sharper, more divisive aroma.
Our Renew candle and Mood Boost pulse point oil both contain lemongrass — which is part of why I reach for these in summer specifically.
Eucalyptus — the indoor option
Eucalyptus contains eucalyptol, which disrupts flies' ability to detect smell — essentially leaving them confused and less able to navigate toward food or people. It's particularly useful indoors near entry points, windows, and kitchen areas.
Our Flow candle and Focus pulse point oil both contain eucalyptus — making them a useful double for outdoor use and indoor deterrence.
Lavender — the gentlest option
Lavender contains linalool, which has demonstrated repellent effects against flies and cockroaches by disrupting insect nervous system signalling. It's not as potent as peppermint or lemongrass but it's the gentlest option and works well in combination with stronger oils.
Our Rest candle and Sleep Aid pulse point oil contain lavender - so your bedtime ritual is also, usefully, deterring insects from your bedroom.
What Doesn't Work
Essential oils don't kill flies. They repel and deter — they create an inhospitable sensory environment that insects avoid. If you have a serious infestation, essential oils will not solve the problem.
Diluted or low-quality oils are ineffective. The science is based on therapeutic-grade essential oils at meaningful concentrations. A candle made with synthetic fragrance — even if it smells like peppermint — won't deliver the same deterrent compounds because the actual plant molecules that deter insects simply aren't present. This is one of the reasons genuine essential oil candles are different from scented candles in a practical, functional sense.
Single-use application wears off. The protective effect of essential oils lasts hours, not days. For outdoor use, reapplication or a continuously burning candle is more effective than a one-time spray.
How to Use Essential Oils as Insect Deterrents
Outdoors — the candle method
This is what I do. Light an essential oil candle on the table or near your seating area when spending time outside. The continuously burning candle disperses the deterrent compounds into the air around you.
The Flow candle — peppermint, eucalyptus and may chang — is my first choice for this. The peppermint content specifically makes it effective for flies and midges.
On the go — pulse point oil
When I'm doing outdoor yoga or walking and can't light a candle, I apply the Focus pulse point oil to my wrists and temples before going outside. The peppermint and eucalyptus in the blend create a personal deterrent zone — and the application to pulse points means the scent is released continuously as your body heat warms the oil.
This also works well for children — applied to clothing rather than directly to skin if you prefer — though always check individual essential oil safety for children and pregnant women before use.
Indoors — near entry points
For deterring flies from coming inside, place a few drops of peppermint or lemongrass oil on cotton wool and position near windowsills, door frames, and bins. Reapply every few hours. Alternatively burn a candle near open windows and doors.
A simple deterrent blend
If you want to make a spray for outdoor furniture or surfaces — not for skin application — mix:
5 drops peppermint essential oil
5 drops lemongrass essential oil
3 drops eucalyptus essential oil
In 100ml water with a teaspoon of vodka or rubbing alcohol to help the oils disperse
Shake well before each use. Spray around seating areas, outdoor tables, and near doorways. Reapply every two to three hours.
Note — this is for surfaces and spaces, not direct skin application. For skin use, essential oils must be properly diluted in a carrier oil.
The Irish Midge Problem
A specific note for Irish summers - midges are a different challenge to houseflies and require a different approach.
Midges are attracted to CO₂ - the carbon dioxide you exhale - which means they find you regardless of what you smell like. Essential oils don't block CO₂ but they do create a sensory interference that makes it harder for midges to locate and land.
Lemongrass and eucalyptus are the most effective for midges specifically. There is also interesting Irish research on bog myrtle — a native Irish plant — which has demonstrated significant midge-repellent properties in recent studies. Bog myrtle essential oil isn't something we use in our blends but it's worth knowing about if midges are your primary concern.
The practical advice for outdoor evenings in Ireland is layered deterrence — a lemongrass-containing candle burning nearby combined with a peppermint or eucalyptus pulse point oil applied to exposed skin areas. Neither alone is a guarantee but together they make a meaningful difference.
The Honest Summary
Essential oils — particularly peppermint, lemongrass and eucalyptus — are genuinely effective fly and insect deterrents when used at meaningful concentrations and reapplied regularly. The science supports this. They work by disrupting insect sensory systems rather than killing insects, which means they're a deterrent rather than an exterminator.
For Irish summer evenings outdoors, a peppermint or lemongrass essential oil candle on the table is the most practical and pleasant approach. For outdoor movement, a pulse point oil containing peppermint or eucalyptus applied before you go out extends the deterrence to your person.
It won't work in every situation. But for making outdoor summer evenings more enjoyable, it works well enough that I keep going back to it every year.
The Wizard & Grace oils most useful for insect deterrence:
Flow candle — peppermint, eucalyptus, may chang — for outdoor tables and seating areas
Renew candle — lemongrass, lavender, grapefruit, sage — particularly effective for flies outdoors
Focus pulse point oil — peppermint, eucalyptus, may chang — apply to pulse points before going outside
Mood Boost pulse point oil — lemongrass, sage, lavender — uplifting and deterring in equal measure
All available at WizardandGrace.com. Free shipping across Ireland on orders over €60.
Frequently Asked Questions
Do essential oils really repel flies?
Yes — certain essential oils, particularly peppermint, lemongrass and eucalyptus, have documented repellent effects against flies. A peer-reviewed study found oils containing menthol, citral and linalool repelled over 75% of flies for up to eight hours at appropriate concentrations. They work by disrupting insects' olfactory systems rather than killing them.
What essential oil keeps flies away best?
Peppermint is the most researched and most consistently effective essential oil for fly deterrence. Lemongrass is particularly effective outdoors and for mosquitoes. Eucalyptus is useful indoors. A combination of all three provides the broadest deterrent effect.
Do essential oil candles repel insects?
Genuine essential oil candles — those made with therapeutic-grade essential oils rather than synthetic fragrance — do disperse deterrent compounds as they burn. Synthetic fragrance candles that merely smell like peppermint or lemongrass do not deliver the same effect because the active plant compounds aren't present.
What essential oils repel midges in Ireland?
Lemongrass and eucalyptus are the most effective for Irish midges. Bog myrtle — a native Irish plant — has shown significant midge-repellent properties in recent Irish research. Layered use of lemongrass candles plus peppermint or eucalyptus pulse point oil is the most practical approach for outdoor summer evenings in Ireland.
Is it safe to use essential oils outdoors around children and pets?
Essential oils should always be used with care around children and pets. Some oils — particularly eucalyptus and peppermint — should not be applied directly to young children's skin. Diffusing outdoors in open air is generally safer than enclosed spaces. Consult a healthcare provider before using essential oils around infants, young children, or pregnant women.
How long do essential oils repel flies?
Research suggests therapeutic-grade essential oils at appropriate concentrations can deter flies for six to eight hours. In practical outdoor use — where scent disperses faster in open air — reapplication or a continuously burning candle every two to three hours is more realistic.
Wizard & Grace essential oil candles and pulse point oils are available at WizardandGrace.com. Every blend formulated using 100% therapeutic-grade essential oils. Handcrafted in Ireland.
