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 working in the air rather than on your skin. It is an EPA-registered active ingredient for nonfood uses (PC Code 109709; CAS 240494-70-6), with safety and performance reviewed for labeled applications as a vapor-phase repellent; for chemical identity and properties, see PubChem. Thermacell leverages metofluthrin in select, scent-free, no-skin-contact [outdoor solutions] to create protective zones that are easy to use and comfortable for active outdoor lifestyles. For ingredient context across our portfolio, see our overview of main ingredients used in Thermacell products.

How Metofluthrin Works as a Mosquito Repellent

>Metofluthrin is highly volatile and evaporates at room temperature, creating an airborne protective zone that can be further dispersed by heat-based devices. This vapor discourages mosquitoes from entering or biting, delivering repellency without direct skin application, as outlined in the EPA’s metofluthrin fact sheet.

Spatial repellency refers to the use of airborne ingredients to create a zone where mosquitoes are deterred from entering or biting. Rather than killing on contact, the vapor reduces mosquito activity, host-seeking, and landings across a defined space, establishing a protective buffer that minimizes bites in and around the zone Achee et al. 2012.

At the molecular level, metofluthrin acts on an insect’s nervous system—it's a pyrethroid that affects sodium channels and is classified under IRAC MoA Group 3A.  In practical use, its doses are intentionally designed to create a gentle behavioral effect, encouraging mosquitoes to keep their distance and helping steer them away from people and outdoor areas.

Thermacell’s outdoor solutions showcase this category’s evolution—clean activation, continuous diffusion, and consistent coverage—especially in our rechargeable lineup and refills designed around convenient, no-skin-contact protection.

Effectiveness and Performance of Metofluthrin

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

Protection can be long-lasting depending on format and dose. Laboratory and field data report strips effective for up to a week, high-dose emanators maintaining efficacy beyond six weeks, and certain indoor-oriented formulations sustaining protection for up to six months, as documented in peer-reviewed residual-effectiveness studies and the EPA registration dossier.

Unlike skin-applied repellents (e.g., 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 you relax outdoors. For skin-applied actives and comparisons, see EPA guidance on DEET.

Safety and Regulatory Considerations

The EPA supports metofluthrin for labeled, non-skin uses and characterizes low mammalian toxicity when devices are used as directed, per its metofluthrin registration and risk assessment and EPA pyrethrins and pyrethroids. As with all pyrethroids, it is a neurotoxicant to insects; Consumer Reports notes that correct use per label is essential for safe operation and optimal results. The CDC provides additional guidance on preventing mosquito bites and using repellents effectively CDC mosquito bite prevention. Device formats are regulated to ensure consistent release rates and exposure profiles, and Thermacell products undergo ongoing safety reviews to meet evolving standards and deliver dependable protection for families and pets.

Best practices:

• Always follow the product label for setup, placement, and refill schedules.
• Operate only in well-ventilated outdoor settings 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 how vapor disperses, potentially changing the size and stability of the protective zone, as summarized in recent spatial repellent reviews.
• Insecticide resistance matters: mosquito populations resistant to pyrethroids like permethrin can show cross-resistance to metofluthrin (up to ~5-fold in some studies), which may reduce performance in specific locales.
• Spatial repellents do not “wall off” unlimited areas; gaps, high winds, or very strong mosquito pressure can permit biting at the edges. For robust protection in challenging settings, integrate spatial repellents with complementary methods such as source reduction, screens, and targeted adulticides.

Role of Metofluthrin in Public Health and Vector Control

Field trials deploying metofluthrin in communities have demonstrated significant reductions in indoor Aedes aegypti densities and biting, 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 can be setting-specific. In practice, spatial repellents complement bed nets, residual sprays, larval control, and personal protection—offering flexible, user-friendly coverage 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 want to protect, allowing several minutes for the zone to establish.
• Monitor airflow: position devices away from strong wind and large fans that can disperse vapor too quickly.
• Check device status and refill levels regularly to maintain uninterrupted protection.
• In high-pressure or resistance-prone areas, pair Thermacell devices with other protective measures (long sleeves, screens, and local vector control guidance).

Frequently Asked Questions

Is metofluthrin safe for 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 typical devices?

Depending on the device and cartridge, protection ranges from several hours per session to multiple weeks for 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 for application to skin, so irritation is uncommon. Avoid direct contact with the liquid and use only as instructed.

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 they serve different use-cases.

What factors affect the effectiveness of metofluthrin products?

Wind, temperature, humidity, and placement all influence how the vapor disperses. For best results, avoid strong airflow and follow setup guidance on the label.