Allethrin

The evidence

Allethrin and its d-isomers are among the oldest synthetic pyrethroids used in mosquito coils and heat emanators. Field studies show real short-range spatial protection, often cutting bites 70 to 90 percent within a small treated zone for a few hours, though efficacy is inconsistent against Aedes and drops off with wind and distance from the device.

• Volatile pyrethroid spatial repellents for preventing mosquito bites: a systematic review and meta-analysis
  2025Meta AnalysisDefinitive evidence

  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.

• An Expert Review of Spatial Repellents for Mosquito Control
  2020ReviewWell-supported evidence

  This is a commissioned expert review, not a single experiment, that pulled together the published evidence on spatial repellents. Spatial repellents are the family of products that put a volatile insecticide into the air around you rather than on your skin, which is the category that includes battery or heat-powered emanators such as Thermacell and the OFF! Clip-On, passive strips, and the older mosquito coil. The review walks through how these devices work, which airborne active ingredients drive them, and what protection they have delivered in controlled and semi-field testing, with the goal of judging whether the category is promising enough for public-health investment.

• Environmental health risks and benefits of the use of mosquito coils as malaria prevention and control strategy
  2018ReviewWell-supported evidence

  The mosquito coil is the oldest and cheapest airborne repellent device, a spiral you light so that it smolders and releases a pyrethroid such as allethrin or pyrethrins into the air. This review weighed both sides of the coil: how much it actually protects against mosquitoes, and what the smoke does to the people breathing it. It is a helpful reality check for anyone reaching for coils as a low-cost area repellent, because it puts modest efficacy next to a real air-quality cost.

• Application of mosquito repellent coils and associated self-reported health issues in Ghana
  2016Field Trial

  Cross-sectional survey of coil users and self-reported respiratory health.

• A systematic review of mosquito coils and passive emanators: defining recommendations for spatial repellency testing methodologies
  2012ReviewWell-supported evidence

  Systematic review of the spatial repellency of mosquito coils and passive emanators.

• Do mosquito coils prevent malaria? A systematic review of trials
  2004ReviewWell-supported evidence

  Systematic review of whether mosquito coils reduce bites and prevent malaria.

• Mosquito coil emissions and health implications
  2003Lab

  Emissions study of six mosquito coil brands and their air-quality and health implications.

• Field evaluation of an area repellent system (Thermacell) against Phlebotomus papatasi and Ochlerotatus caspius in Sanliurfa Province, Turkey
  2003Field TrialWell-supported evidence

  Field trial of the allethrin Thermacell area repellent at multiple distances over six hours.

• Field efficacy of mosquito coil formulations containing d-allethrin and d-transallethrin against indoor mosquitoes especially Culex quinquefasciatus
  1990Field TrialWell-supported evidence

  Field trial of d-allethrin and d-transallethrin mosquito coils in Malaysian homes, in a Culex-dominated setting.

Products using it

Thermacell

Thermacell Patio Shield MR300 Mosquito Repeller

74

Allethrin 21.97%

Coverage & effectiveness

Protected zone~15 ft zone

Fewer bitesest.70–92%

Thermacell

Thermacell Backpacker Mosquito Repeller

74

Allethrin 21.97%

Coverage & effectiveness

Protected zone~15 ft zone

Fewer bitesest.70–92%

PIC

PIC Mosquito Repellent Coils

47

Allethrin 0.25%

Coverage & effectiveness

Protected zone~5 ft zone

Fewer bitesest.30–60%

Coghlan's

Coghlan's Mosquito Coils

47

Allethrin 0.25%

Coverage & effectiveness

Protected zone~5 ft zone

Fewer bitesest.30–60%

Regulatory notes

Source: EPA SRS active ingredient list export. Minimum risk (25(b)) status is applied separately when applicable.