The most effective repellents for both flies and mosquitoes are DEET, picaridin, and oil of lemon eucalyptus applied to skin, combined with physical barriers like fans and area repellent devices for outdoor spaces. DEET alone has over 500 registered products and provides two to twelve hours of mosquito protection depending on concentration. But the best approach combines a skin-applied repellent with environmental strategies, since no single method covers every situation.
How Repellents Actually Work
Mosquitoes and flies find you primarily through smell. They detect carbon dioxide from your breath, body heat, and the hundreds of volatile chemicals your skin releases. Repellents work by interfering with this detection system. DEET, picaridin, and several plant-derived compounds activate a specific odor receptor in mosquitoes that also responds to methyl jasmonate, a chemical plants produce as a defense against insects. In other words, these repellents hijack a receptor that insects already use to avoid plant defenses, triggering an avoidance response.
This is why DEET and picaridin share structural similarities with plant defense compounds. They’re essentially mimicking a danger signal that insects are already wired to avoid.
Skin-Applied Repellents Ranked
The EPA registers seven active ingredients for skin-applied insect repellents. They vary significantly in how long they last and how broadly they work.
- DEET remains the benchmark. Products range from 5% to nearly 100% concentration, and protection lasts anywhere from two to twelve hours depending on that concentration. A 25-30% product covers most people for a full day outdoors.
- Picaridin performs comparably to DEET at similar concentrations, with about 40 products on the market. It’s odorless, doesn’t damage plastics or synthetic fabrics (DEET can), and feels less oily on skin.
- Oil of lemon eucalyptus (OLE) provides protection comparable to low-concentration DEET against mosquitoes found in the United States. Its active compound, PMD, is the only plant-derived ingredient the CDC lists alongside synthetic options. It needs more frequent reapplication than higher-concentration DEET or picaridin.
- IR3535 also matches low-concentration DEET in mosquito protection and has roughly 45 registered products. It’s common in European formulations and has a long safety track record.
- 2-undecanone, originally derived from wild tomatoes, matched 7% DEET against several mosquito species over a six-hour test period. On treated clothing, it performed equally to 7% DEET for up to eight days. It fell short of 15% DEET against yellow fever mosquitoes, so it works best in lower-pressure environments.
- Catnip oil and citronella oil round out the registered list but have far fewer products and shorter protection windows. Citronella applied to skin typically lasts under two hours.
What Works for Flies Specifically
Mosquito repellents get most of the research attention, but flies respond to a partially overlapping set of strategies. DEET and picaridin do repel house flies and horse flies, though less reliably than they repel mosquitoes. For house flies specifically, lemongrass essential oil has shown strong repellent and adulticidal activity in controlled studies, outperforming even some synthetic insecticides. Peppermint and clove oil also deter flies, though published efficacy data is thinner.
The practical difference with flies is that they’re stronger fliers than mosquitoes and more persistent around food sources. Skin repellents help, but removing attractants (garbage, pet waste, uncovered food) and using physical barriers like screens or fans tends to matter more for fly control than for mosquito control.
Area Repellent Devices
If you’re trying to protect a patio, campsite, or backyard gathering, area repellent devices heat a volatile compound that creates a protective zone around the unit. Fuel-powered devices like Thermacell repellers protect roughly 225 square feet, about the size of an average deck. Their multi-insect versions create a 15-foot zone against mosquitoes and a 10-foot zone against black flies and no-see-ums. Rechargeable models cover about 110 square feet at maximum effectiveness, with protection declining beyond 10 feet.
Larger property systems use multiple repeller units, each creating a 20-foot zone (10-foot radius in every direction) for a minimum of 315 square feet per unit. These work well for defined outdoor areas but won’t protect you on a hike or anywhere you’re moving through space.
Fans: The Overlooked Physical Barrier
A simple electric fan is surprisingly effective against mosquitoes. Mosquitoes fly at speeds between 0.9 and 3.6 miles per hour, and they avoid areas where wind speeds approach or exceed their flying ability. In testing, a fan producing wind at just 0.6 meters per second (about 1.3 mph) significantly reduced mosquito landings even without any chemical repellent involved. The wind both makes it physically difficult for mosquitoes to navigate and disperses the carbon dioxide and body odor plumes they use to find you.
For a backyard dinner or porch sitting, positioning an oscillating fan at ground-to-waist level (where mosquitoes tend to approach) provides a meaningful layer of protection on top of whatever repellent you’re wearing.
Citronella Candles: Limited Protection
Citronella candles are one of the most popular outdoor mosquito products, but the data is underwhelming. In field testing against Aedes mosquitoes, citronella candles reduced bites by about 42% compared to no candles at all. That sounds decent until you note that subjects still received an average of 6.2 bites per five minutes sitting near a citronella candle, compared to 10.8 bites with no candle. Plain, unscented candles performed nearly as well as citronella incense, reducing bites by a similar margin, likely because any flame produces CO2 and heat that can partially confuse mosquito navigation.
Citronella candles are better than nothing, but they’re not a substitute for skin-applied repellent or an area device if mosquito pressure is significant.
Light Bulbs and Color: Less Impact Than Expected
Switching to warm-toned or amber LED bulbs is frequently recommended to reduce insect attraction around outdoor lights. The theory is sound (insects are generally more attracted to shorter, blue-spectrum wavelengths), but a large review of the evidence found that the benefits of changing light color or dimming are “ambiguous and frequently negligible” in practice. You won’t attract zero insects with a warm bulb, and you won’t dramatically reduce the ones that find you. If outdoor lighting matters to you, warmer tones are a reasonable default, but don’t expect it to replace actual repellent strategies.
Combining Methods for Best Results
The most effective approach layers multiple strategies. For your body, a skin-applied repellent containing DEET, picaridin, or OLE handles the personal protection. For a stationary outdoor area, add a fan or an area repellent device. For your property overall, eliminate standing water (mosquito breeding habitat includes anything holding water for more than a few days), keep garbage sealed, and maintain screens on windows and doors.
Treating clothing with permethrin adds another layer. Permethrin is not a skin repellent but bonds to fabric fibers, killing or repelling insects on contact. A single treatment lasts through multiple washes and is particularly useful for outdoor work clothes, hiking gear, and camping equipment. Combined with a skin-applied repellent on exposed areas, treated clothing provides close to complete protection in most environments.