What is metofluthrin? Mosquito repellent ingredient explained.

Introduction to Metofluthrin

Metofluthrin is a synthetic pyrethroid insecticide used as a volatile spatial repellent, designed to keep mosquitoes away by acting in the air rather than on the skin. It is an EPA-registered active ingredient for non-food uses, with PC Code 109709 and CAS 240494-70-6, whose safety and performance have been reviewed for labeled vapor-phase repellent applications. For its chemical identity and properties, PubChem can be consulted.

Thermacell uses metofluthrin in some scent-free, no-skin-contact outdoor solutions to create easy-to-use and comfortable protective zones for active outdoor lifestyles. To understand the context of ingredients across our range, see our overview of the primary ingredients used in Thermacell products.

How Metofluthrin Works as a Mosquito Repellent

Metofluthrin is highly volatile and evaporates at ambient temperatures, creating a protective zone in the air that can be further dispersed by heat-based devices. This vapor deters mosquitoes from entering or biting, providing repellency without direct skin application, as described in the EPA fact sheet on metofluthrin.

Spatial repellency refers to the use of airborne ingredients to create a zone where mosquitoes are deterred from entering or biting. Instead of killing on contact, the vapor reduces mosquito activity, host-seeking, and landings within a defined space, establishing a protective barrier that minimizes bites within and around that zone.

At a molecular level, metofluthrin acts on insects’ nervous systems. It is a pyrethroid that affects sodium channels and is classified under IRAC mode of action Group 3A. In practical use, its dosages are intentionally designed to create a mild behavioral effect, encouraging mosquitoes to stay away and helping to divert them from people and outdoor areas.

How Thermacell-type Spatial Devices Create a Protective “Zone”

1. Insert a metofluthrin cartridge into the device.

2. Turn on the device.

3. The repellent diffuses into the surrounding area.

4. Within minutes, mosquitoes leave the area and do not re-enter; maintain good placement and consider airflow for best results.

Applications and Product Types Containing Metofluthrin

Metofluthrin appears in numerous formats, including Thermacell refillable repellents, plastic strips or emanators, clip-on devices, coils, impregnated nets, and area repellent mats, reflecting over a decade of innovation in spatial repellency technology summarized in recent reviews on spatial repellents and WHO guidelines for their testing.

Formats, Doses, Duration, and Common Uses

Thermacell's outdoor solutions showcase the evolution of this category: clean activation, continuous diffusion, and consistent coverage, especially in our rechargeable line and refills designed for convenient, no-skin-contact protection.

Metofluthrin Efficacy and Performance

Independent and programmatic reviews consistently show strong spatial performance. In controlled and semi-field evaluations, metofluthrin-treated devices and traps have yielded 91–97% reductions in mosquito landings, demonstrating robust area-level protection across various species and environments, according to an expert review by IVCC.

Protection can be long-lasting depending on the format and dose. Laboratory and field data indicate that strips can be effective for up to a week, high-dose emanators can maintain efficacy for over six weeks, and certain indoor-oriented formulations can sustain protection for up to six months, according to peer-reviewed studies on residual efficacy and EPA registration documentation.

Unlike skin-applied repellents like DEET, which protect only treated skin surfaces, metofluthrin works from the air to protect the space around you, reducing the need for repeated rubbing or spraying while enjoying the outdoors. To learn more about skin-applied ingredients and comparisons, refer to the EPA guide on DEET.

Safety and Regulatory Considerations

The EPA supports the use of metofluthrin for labeled non-skin-contact applications and describes low mammalian toxicity when devices are used as directed, according to their metofluthrin registration and risk assessment and EPA information on pyrethrins and pyrethroids. Like all pyrethroids, it is a neurotoxicant for insects. Consumer Reports notes that correct use according to the label is essential for safe operation and optimal results. The CDC offers additional guidance for preventing mosquito bites and using repellents effectively. Device formats are regulated to ensure consistent release rates and exposure profiles, and Thermacell products undergo continuous safety reviews to meet evolving standards and provide reliable protection for families and pets.

Best Practices

• Always follow the product label for setup, placement, and refill scheduling.

• Use only outdoors in well-ventilated areas, as directed.

• Store refills and devices out of reach of children and pets when not in use.

Limitations and Environmental Impact

Environmental variables, especially temperature, humidity, and airflow, can alter vapor dispersion, potentially changing the size and stability of the protective zone, as summarized in recent reviews on spatial repellents.

Insecticide resistance matters: mosquito populations resistant to pyrethroids like permethrin may show cross-resistance to metofluthrin, up to about 5 times in some studies, which can reduce performance in specific areas.

Spatial repellents do not "close off" unlimited areas; gaps, strong winds, or very high mosquito pressure can allow bites at the edges. For robust protection in challenging conditions, integrate spatial repellents with complementary methods such as source reduction, bed nets, and targeted adulticides.

Role of Metofluthrin in Public Health and Vector Control

Field trials that have deployed metofluthrin in communities have demonstrated significant reductions in Aedes aegypti density and bites indoors, supporting its value as part of integrated vector management. While entomological impacts are clear in many contexts, large-scale effects on disease transmission remain under study and may be environment-dependent. In practice, spatial repellents complement bed nets, residual spraying, larval control, and personal protection, offering flexible and user-friendly coverage in places where people gather, rest, or work.

Best Practices for Using Metofluthrin-Based Repellents

Read and follow the label; place devices near the center of the area you wish to protect, allowing several minutes for the zone to establish.

Control airflow: position devices away from strong wind and large fans that can disperse the vapor too quickly.

Regularly check device status and refill levels to maintain uninterrupted protection.

In areas with high mosquito pressure or prone to resistance, combine Thermacell devices with other protective measures, such as long sleeves, mosquito nets, and local vector control recommendations.

Frequently Asked Questions

Is metofluthrin safe to use around children and pets?

Yes, when used strictly as directed on the label. Its vapor-phase design avoids skin application, and EPA reviews support low mammalian toxicity for labeled outdoor uses.

How long does metofluthrin protection last in common devices?

Depending on the device and cartridge, protection can range from several hours per session to several weeks in passive emanators. Check the product label for exact duration.

Can metofluthrin cause skin irritation or other side effects?

It is designed for spatial use, not skin application, so irritation is rare. Avoid direct contact with the liquid and use only as directed.

How does metofluthrin compare to skin-applied repellents?

Metofluthrin creates a protective vapor barrier in the air, covering areas where people gather, while traditional skin-applied repellents protect only treated skin. Both are effective when used as directed but serve different purposes.

What factors affect the effectiveness of metofluthrin products?

Wind, temperature, humidity, and placement all influence how the vapor disperses. For best results, avoid strong drafts and follow the label's setup instructions.