Transfluthrin
Cyclopropanecarboxylic acid, 3-(2,2-dichloroethenyl)-2,2-dimethyl-, (2,3,5,6-tetrafluorophenyl)methyl ester
Transfluthrin is a volatile synthetic pyrethroid used as the active in passive emanator strips and coil-free area devices that release vapor without heat or batteries. It is not applied to skin. It evaporates readily at room temperature and forms a protective zone of vapor that repels flying insects. It has fast knockdown and low environmental persistence. Like all pyrethroids it is highly toxic to fish and aquatic invertebrates, and several jurisdictions restrict its outdoor use for that reason.
How it works
Transfluthrin is a fast-acting Type I pyrethroid that binds insect voltage-gated sodium channels and holds them open, producing knockdown and spatial repellency in the vapor phase. Its high volatility lets it work passively, evaporating from a treated strip or card to protect an area rather than a surface, while its low persistence means it does not linger long once the source is removed.
Safety around dogs & cats
Cats are the sensitive species for pyrethroids because they cannot glucuronidate them efficiently (ASPCA, Pet Poison Helpline, VCA), so keep cats away from a running strip or card and never let one mouth the source. Outdoor vapor exposure from an emanator is lower risk than a skin or spot-on product, and dogs tolerate pyrethroids well (Merck Veterinary Manual), but cats warrant the most caution. Do not run a device in an enclosed space with a pet bird, and never apply the product to an animal.
Moderate confidence. Ratings from ASPCA Animal Poison Control, the Pet Poison Helpline, and published veterinary toxicology. This is general information, not veterinary advice. If your pet is exposed, call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435.
The evidence
Laboratory and semi-field studies (for example PMC10531799) show transfluthrin vapor repels and knocks down mosquitoes, including some pyrethroid-resistant Aedes aegypti, over a confined zone. Like other emanators it delivers area protection rather than the whole-body coverage of a skin repellent.
- Volatile pyrethroid spatial repellents for preventing mosquito bites: a systematic review and meta-analysis2025Meta 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 Control2020ReviewWell-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.
Regulatory notes
EPA has assessed transfluthrin for passive personal and spatial emanator uses (for example the Personal Insect Repellent Kit, in which the active is released passively as a vapor) and concluded the proposed vapor-release use did not raise risk concerns for terrestrial or aquatic organisms at labeled use. Because of its aquatic ecotoxicity, some jurisdictions limit it to enclosed or semi-enclosed spaces.
Safety notes
Not skin-applied, so dermal sensitization and irritation are not the relevant routes. The practical human caution is inhalation of the vapor, so use in ventilated conditions and avoid breathing the stream directly. Keep sources away from water and aquariums.