Study summary
Volatile pyrethroid spatial repellents for preventing mosquito bites: a systematic review and meta-analysis
Denz A, et al. (Liverpool School of Tropical Medicine)
Read the original paper- Study type
- Meta Analysis
- Year
- 2025
- Published in
- eBioMedicine (2025), 119:105891, PMC12789705
- Evidence strength
- Definitive evidence
Summary
This is the most rigorous look at the whole category to date: a systematic review and meta-analysis that pooled data from 58 eligible publications on volatile pyrethroid spatial repellents, the airborne-emanator products built on actives such as transfluthrin, metofluthrin, and allethrin. For 50 of those studies the authors combined individual mosquito-level records, more than 1.7 million mosquitoes in total, along with satellite weather data on temperature, humidity, and wind, so they could estimate an overall protective efficacy and see how it shifts by product format, active ingredient, mosquito species, and indoor versus outdoor setting. This is the single best study for setting honest expectations about what these devices deliver on average.
Key findings
Pooled across all the evidence, volatile pyrethroid spatial repellents provided an average of about 56 percent protective efficacy against mosquito bites, with a confidence interval roughly from 50 to 62 percent. Crucially for realistic backyard expectations, protection was highest in the most controlled setups and stepped down as conditions got more real: around 58 percent in semi-field arenas but closer to 50 percent in open field studies. In plain terms, a typical emanator cuts your bites by roughly half on average, not the 90-plus percent seen in the most controlled vector trials. That is genuinely useful protection, and it also explains why some individual studies report much higher numbers, since those are usually the sheltered, best-case conditions rather than the everyday average.
Limitations
Even a careful meta-analysis is only as consistent as its inputs, and the underlying studies varied widely in devices, actives, mosquito species, and how bites were counted, which shows up as real heterogeneity around that 56 percent average. The headline figure is entomological protection, how many fewer mosquitoes bite, rather than a direct measure of reduced disease. And the same weather analysis that strengthens the review underlines the category's core weakness, that airborne repellents lean on holding active ingredient in the air, so wind and open space pull performance toward the lower end of the range.