Mosquito coils containing pyrethroid insecticides are the most effective thing you can burn to repel mosquitoes, reducing bites by up to 96% when placed within a foot of where you’re sitting. But they’re not your only option. Citronella, certain herbs, and even coffee grounds all produce smoke that mosquitoes dislike to varying degrees. The key differences come down to how well each one actually works, how long it lasts, and what you’re breathing in along with the mosquitoes.
Pyrethroid Mosquito Coils
Standard mosquito coils sold at hardware stores and online typically contain a synthetic insecticide called d-allethrin at concentrations between 0.1% and 0.2%. These coils don’t just repel mosquitoes. They actively drive them away from the area and inhibit feeding. In field tests against common mosquito species, pyrethroid coils achieved feeding inhibition rates of 91% to 100%, meaning nearly every mosquito that entered the area left without biting.
A single coil burns for roughly 5 to 8 hours depending on the brand, making them practical for a full evening outdoors. Placement matters more than most people realize. When coils were tested at various distances from a person, they cut feeding rates most dramatically at about one foot away (only 4% of mosquitoes fed, compared to 86% with no coil). Protection remained significant up to 20 meters away, roughly 65 feet, but dropped off completely at 30 meters. For the best results, place the coil on the ground or a table within a few feet of where you’re sitting, upwind if there’s a breeze.
Some coils use natural pyrethrins (extracted from chrysanthemum flowers) instead of synthetic pyrethroids. These botanical versions performed similarly in repelling mosquitoes from the area, though natural pyrethrins at low concentrations have less knockdown effect, meaning they push mosquitoes away rather than killing them outright.
Citronella Candles and Diffusers
Citronella is probably the first thing that comes to mind when you think of natural mosquito repellents, and it does work. Just not as well as most people assume. In controlled testing, citronella candles reduced mosquito landings by only 14% indoors. Citronella diffusers, which release the oil as a vapor rather than relying on candle smoke, performed much better at 68% repellency.
The difference comes down to concentration. A citronella candle releases a relatively small amount of the active oil into the air compared to a purpose-built diffuser or a citronella coil. If you’re going the citronella route outdoors, coils infused with citronella oil will outperform a standard citronella candle. Grouping multiple candles close together can help, but you’re still working with a weaker repellent than pyrethroids.
Herbs and Plant-Based Smoke
Burning bundles of dried herbs is a popular DIY approach, and some plants do contain compounds that mosquitoes avoid. The most commonly recommended options include:
- Rosemary: Produces aromatic smoke with compounds that mosquitoes find irritating. Toss fresh or dried sprigs directly onto a fire or grill coals.
- Sage: Another strong-smelling herb that works similarly to rosemary when burned in bundles.
- Lavender: Contains linalool, a compound shown to significantly repel mosquitoes in lab settings.
- Lemongrass: The plant citronella oil comes from. Burning the stalks releases the same repellent compounds as citronella products.
The practical limitation with herbs is consistency. Tossing a sprig of rosemary on a campfire creates a burst of fragrant smoke that dissipates quickly. You’d need to keep adding material regularly to maintain any real effect, and the concentration of repellent compounds reaching you depends entirely on wind direction and how much you’re burning. Herbs work best as a supplement, adding them to a fire you’re already sitting near, rather than as a standalone strategy.
Coffee Grounds
Burning used coffee grounds is a folk remedy that actually has some scientific backing, though not quite in the way most people use it. Research published in Parasites & Vectors found that coffee extracts strongly deterred female mosquitoes from laying eggs, and gravid females actively avoided areas with high concentrations of coffee. The study focused on the Asian tiger mosquito, a common daytime-biting species.
The catch is that this research tested coffee in liquid form as an egg-laying deterrent, not burned coffee smoke as an airborne repellent. Smoldering coffee grounds do produce thick, pungent smoke that many people swear keeps mosquitoes at bay. The smoke itself may provide some benefit simply because mosquitoes generally avoid dense smoke of any kind. To try it, spread used grounds on a flat dish or piece of foil and let them dry completely, then light them so they smolder slowly rather than flame up.
Plain Smoke and Campfires
Any fire produces smoke, and smoke alone does reduce mosquito activity in the immediate area. Mosquitoes navigate partly by detecting carbon dioxide and body odors, and thick smoke disrupts their ability to find you. A campfire or fire pit will provide some passive protection just by existing, especially if you’re sitting in the smoke plume. Adding green or slightly damp wood increases smoke output, though this also increases the amount of particulate matter you’re inhaling.
Health Tradeoffs Worth Knowing
Burning anything to repel mosquitoes means breathing in fine particulate matter. Research from the National Institute of Environmental Health Sciences found that burning a single mosquito coil releases the same amount of fine particles (PM2.5) as burning 75 to 137 cigarettes. That number sounds alarming, and it should inform how you use coils. Burning them outdoors in a ventilated space is very different from burning them in a closed room, but regular nightly use in a poorly ventilated bedroom is a real respiratory concern over time.
Citronella candles and herb bundles produce far less particulate matter than a smoldering coil, simply because they burn less material over a shorter period. If you’re choosing between options for a screened porch or semi-enclosed patio, citronella or herb smoke is the gentler choice for your lungs, even if the mosquito protection is weaker.
What Actually Works Best Outdoors
For a backyard dinner or evening on the patio, a pyrethroid coil placed within a few feet of your seating area gives you the strongest protection from a single burned product. For a campfire setting, tossing rosemary, sage, or lemongrass onto the coals adds a layer of repellency on top of the smoke you’re already producing. Citronella candles are better than nothing, but only modestly. They’re the least effective standalone option despite being the most widely marketed one.
Combining methods works best. A coil near your feet, a citronella candle on the table, and a fan creating airflow (mosquitoes are weak fliers and struggle in even a light breeze) will do far more together than any single product alone. And for anything beyond casual protection, a DEET or picaridin spray applied to your skin will always outperform ambient smoke, because it works regardless of wind direction or how far you wander from the fire.