Citronella does repel gnats, but its effects are mild and short-lived compared to synthetic repellents. If you’re dealing with a few gnats on the patio, a citronella candle or spray can help. If you’re heading into heavy gnat territory, you’ll want something stronger.
How Citronella Works on Insects
Citronella oil contains a compound called citronellal that directly activates sensory channels in insect nerve cells. Researchers found that citronellal triggers specific pore-like proteins (called TRP channels) on the surface of olfactory neurons, flooding them with calcium and other charged molecules. This essentially overwhelms the insect’s smell system, making it harder for gnats and mosquitoes to detect the carbon dioxide and body odors they use to find you. The mosquito version of this channel, TRPA1, is directly activated by citronellal, which is why the compound works across multiple biting insect species, gnats included.
This is a different mechanism than simply masking your scent. Citronella actively irritates the insect’s sensory system, creating an aversion response rather than just hiding you from detection.
How Effective Citronella Actually Is
The short answer: moderately effective at close range, for a limited time. In a study published in Frontiers in Insect Science, volunteers using a citronella candle reported a 42% decrease in insect bites compared to a plain candle with no essential oils. Some essential oil candle formulations reached up to 56% reduction in insect attraction. Those numbers are meaningful but far from complete protection.
The bigger limitation is duration. The EPA has not formally evaluated citronella oil for repellent effectiveness, and protection time data for citronella-based products is listed as “N/A” in standardized comparisons. In practice, citronella oil applied to skin tends to evaporate within 30 to 60 minutes, requiring frequent reapplication. Candles only create a small zone of protection directly around the flame, and any breeze disperses the volatile oils quickly.
For outdoor dining or a calm evening on the porch, citronella candles can take the edge off gnat activity. For a hike, yard work, or anywhere you’re moving around, topical application of citronella oil offers slightly better coverage but still fades fast.
Citronella vs. DEET, Picaridin, and OLE
If gnats are a serious nuisance, the performance gap between citronella and proven synthetic repellents is wide. DEET provides 2 to 12 hours of protection depending on concentration. Picaridin lasts 5 to 14 hours and is considered more effective than DEET specifically at repelling flies and fly-like insects, which makes it a strong choice for gnats. Oil of lemon eucalyptus (OLE), the most effective plant-based option with EPA registration, provides about 2 hours of protection per application.
Citronella sits well below all three. It works through a real biological mechanism, but the active compounds simply don’t persist on skin or in the air long enough to compete. If you prefer natural options and gnats are your main concern, OLE is a better bet. If you want the longest protection with the least reapplication, picaridin is the standout.
Getting the Most From Citronella
If you still want to use citronella, a few practical details make a difference. Topical citronella sprays or lotions outperform candles because the oil stays closer to your skin rather than drifting into the air. Reapply every 30 to 60 minutes. Higher concentrations of citronella oil provide stronger initial repellency, so check the percentage on the label rather than assuming all “citronella” products are equivalent.
For candles, placement matters. Set them close to where you’re sitting, ideally within a couple of feet, and use multiple candles if you’re covering a larger area. On windy days, candles lose most of their effectiveness because the volatile compounds blow away before reaching the gnats near you. Combining citronella candles with a fan pointed at your seating area can actually work well, since gnats are weak fliers and even a light breeze disrupts their ability to land.
Safety Around Pets
Citronella is generally safe for people at typical repellent concentrations, though it can cause mild skin irritation in some individuals, especially with repeated application. The bigger concern is pets, particularly cats.
Cats lack a liver enzyme needed to break down many essential oil compounds, making them especially vulnerable to toxicity. Symptoms of essential oil exposure in cats include drooling, vomiting, tremors, wobbliness, respiratory distress, and in severe cases, liver failure. The higher the concentration of the oil, the greater the risk. Concentrated citronella oil should never be applied directly to a cat’s fur or skin, and even passive diffusers can cause respiratory irritation, watery eyes, and nausea in sensitive cats.
Dogs are generally more tolerant than cats but can still experience digestive upset if they lick citronella oil off surfaces or skin. If you’re using citronella candles outdoors with pets nearby, the risk is low. If you’re using concentrated oils, diffusers, or sprays indoors, keep cats out of the room and ensure good ventilation.