Thermacell Devices and How They Work

Dr. Kristie Gering • June 2, 2026

Learn about effective ways to manage mosquitoes during peak seasons! Thermacell devices offer proven, and safe protection against those pesky mosquitoes.

How Thermacell Devices Work


Thermacell devices are spatial repellents, meaning they don't primarily protect your skin like DEET. Instead, they create a protective zone in the surrounding air by slowly vaporizing a volatile insecticide/repellent. Mosquitoes entering that zone become disoriented, repelled, or exposed to concentrations that impair their ability to locate and bite humans. 

 

Depending on the model, Thermacell devices can use different active ingredients: 


What Exactly Are These Chemicals? 


1. Metofluthrin

Metofluthrin is a synthetic pyrethroid developed specifically to be highly volatile, allowing it to evaporate into the air and function as a spatial repellent. It is EPA-registered for mosquito control and is considered one of the most effective vapor-phase mosquito repellents available. 

 

Mechanism: 

Acts on insect voltage-gated sodium channels 

Disrupts normal nerve signaling 

Causes avoidance behavior, knockdown, and death at higher exposures 

Mosquitoes do not need to touch it; inhalation of tiny amounts is sufficient to alter behavior. 

 

2. D-Allethrin 

Allethrin is an older synthetic pyrethroid derived from the chemistry of natural pyrethrins found in chrysanthemum flowers. Like metofluthrin, it affects insect nerve sodium channels and is released by heating impregnated mats. 

 

How Effective Is It? 

Laboratory Studies 

A 2019 study evaluating metofluthrin spatial repellents found: 

  • 80% reduction in mosquito bites.
  • 40% mosquito knockdown during arm-in-cage testing.

 

Multiple field studies show: 

  • Landing rates reduced 48-67% depending on concentration and deployment. 
  • Mosquito populations reduced about one-third in community deployment studies. 
  • Human biting rates reduced up to 79-94% in some real-world deployments. 
  • Effective even against some pyrethroid-resistant mosquitoes. 


 

Thermacell devices generally perform best in these conditions: 

  • Little or no wind
  • Patios and decks
  • campsites
  • Stationary activities 

 

Performance decreases substantially when wind disperses the vapor cloud. This is a common theme in both user reports and field testing. 

 

Is it Toxic?

In standard toxicology testing, Metofluthrin has mixed toxicity reports, but overall low toxicity reports. With low oral and dermal toxicity, slight inhalation toxicity, and minimal skin and eye irritation. The EPA classified metofluthrin as having relatively low mammalian toxicity at expected exposure levels. 

 

Like all pyrethroids, metofluthrin and allethrin target sodium channels. At sufficiently high exposures, pyrethroids can cause: 

  • Paresthesias (tingling) 
  • Burning sensations 
  • Dizziness 
  • Headache 
  • Tremor 
  • Nausea 

 

These effects are usually temporary. Pyrethroid-induced paresthesia is a well-known phenomenon among pesticide toxicologists. 

 

One reviewer described transient numbness/tingling after spilling concentrated metofluthrin refill liquid on their skin. While anecdotal, it is consistent with known pyrethroid neurotoxicity. 

 

Long-Term Human Toxicity:

This is where evidence is less complete. 

 

Current regulatory reviews generally conclude: 

  • No convincing evidence of carcinogenicity at expected consumer exposures. 
  • No evidence of significant reproductive toxicity at typical exposures. 
  • No evidence that occasional outdoor use causes chronic neurologic disease. 

 

However, Long-term human exposure studies are limited. Most data come from animal toxicology and occupational exposure literature. Pyrethroids as a class remain under active investigation regarding potential neurodevelopmental effects from chronic exposure. 

 

Effects on Pets:

Cats are generally the most sensitive species to pyrethroids because of reduced glucuronidation capacity. Dogs appear less sensitive but can develop neurologic signs after significant exposure.  While Thermacell products are EPA-approved when used according to directions, concentrated refill liquids should be considered potentially hazardous if Ingested, applied directly, or spilled on pets 

 

Environmental Toxicity and Impacts on Animals.. .

This is probably the biggest concern. Like many pyrethroids, Metofluthrin is highly toxic to aquatic life, fish and aquatic invertebrates in particular.

 

With animals such as Pollinators the situation is more complicated. Laboratory toxicology suggests pyrethroids can be harmful to bees and other insects. However, one 2024 study examining airborne metofluthrin from Thermacell E90 devices found no measurable impairment of honey bee learning or memory under the study conditions. 

 

That does not prove absence of environmental effects, but it suggests that vapor-phase exposure may be less harmful to bees than direct insecticide spraying. 

 


Overview


Ranking mosquito control methods by efficacy: 

  1. Thermacell (metofluthrin) 
  2. DEET or picaridin on skin 
  3. Permethrin-treated clothing 
  4. Fans 
  5. Citronella/candles (far less effective) 

 

Thermacell's biggest strengths are: 

  • It's highly effective 
  • No skin application 
  • Good user compliance 
  • Strong field data 

 

Its biggest drawbacks are: 

  • Uses a neuroactive pyrethroid 
  • Not ideal around ponds, streams, or aquatic ecosystems 
  • Potential impacts on non-target insects 
  • Exposure is environmental rather than targeted to skin 

 

For a healthy adult sitting on a deck a few evenings per week, the toxicologic risk appears quite low based on current evidence. For someone with chemical sensitivities, neurologic illness, or a strong desire to minimize pesticide exposure, alternatives such as fans, source reduction, screened spaces, and topical picaridin may be preferable. 

 

The Bottom Line :

Current evidence supports Thermacell products as Highly effective for reducing mosquito bites. And to be low risk for acute toxicity for most adults when used as directed. However, as with any pesticide, the safety of exposure to infants and young children is less clear and may warrant caution. Fans and screened porches are safe non-toxic alternatives. 

Potentially harmful to aquatic organisms and some non-target insects. Not adequately studied for decades-long chronic inhalation exposure. Best viewed as a pesticide-based spatial repellent rather than a "natural" mosquito control method. 

 



References 
EPA. Metofluthrin Pesticide Fact Sheet. U.S. Environmental Protection Agency. 2006. 
Summary: Regulatory toxicology review supporting registration of metofluthrin in consumer mosquito-repellent products. Reports low acute mammalian toxicity at labeled exposures, while noting high toxicity to aquatic organisms and insects. Provides toxicology, environmental fate, and risk assessment data.
https://www3.epa.gov/pesticides/chem_search/reg_actions/registration/fs_PC-109709_01-Sep-06.pdf 
 
Health Canada. Evaluation Report ERC2015-01: Metofluthrin. Pest Management Regulatory Agency. 2015. 
Summary: Independent governmental review concluding that metofluthrin has low acute oral and dermal toxicity, slight inhalation toxicity, minimal skin irritation, and minimal eye irritation under expected use conditions.
https://www.canada.ca/en/health-canada/services/consumer-product-safety/reports-publications/pesticides-pest-management/decisions-updates/evaluation-report/2015/metofluthrin-erc2015-01.html 
 
Lucas JR, Shono Y, Iwasaki T, et al. Field and Laboratory Evaluation of Metofluthrin Spatial Repellents. 
Summary: Demonstrated substantial reductions in mosquito landing and biting rates using metofluthrin vapor-emitting devices in outdoor settings. Frequently cited as foundational evidence supporting spatial repellent technology.
https://academic.oup.com/jinsectscience/article/24/5/7/7831962 
 
Ogoma SB, Moore SJ, Maia MF. A Systematic Review of Mosquito Spatial Repellents. 
Summary: Comprehensive review of spatial repellent research. Reports reductions in mosquito biting, host-seeking behavior, and disease transmission risk associated with metofluthrin and related pyrethroid repellents.
https://www.ivcc.com/wp-content/uploads/2020/08/An-Expert-Review-of-Spatial-Repellents-for-Mosquito-Control.pdf 
 
Couvillon MJ, et al. Airborne Metofluthrin Does Not Impact Foraging Honey Bees. Journal of Insect Science. 2024. 
Summary: Evaluated potential effects of airborne metofluthrin on honey bee behavior. Found no measurable impairment in foraging performance under study conditions, though further ecological research is warranted.
https://pmc.ncbi.nlm.nih.gov/articles/PMC11497606/ 
 
Couvillon MJ, et al. A Volatilized Pyrethroid Insecticide from a Mosquito Repelling Device Does Not Affect Honey Bee Foraging and Recruitment. Journal of Insect Science. 2023. 
Summary: Study of Thermacell-style pyrethroid vapor technology. No significant effects were observed on honey bee foraging frequency, recruitment, or persistence behaviors.
https://academic.oup.com/jinsectscience/article/23/6/11/7458966 
 
EPA. Pyrethroids: Human Health and Ecological Risk Assessment. U.S. Environmental Protection Agency. 2020. 
Summary: Class-wide review of pyrethroid insecticides. Notes generally low mammalian toxicity compared with older pesticide classes but significant toxicity to aquatic organisms and some non-target insects.
https://www.epa.gov/pesticides/epa-addresses-human-health-and-ecological-risks-posed-13-pyrethroids 
 
California Office of Environmental Health Hazard Assessment (OEHHA). Metofluthrin Toxicological Review. 
Summary: Review prepared for California regulatory agencies evaluating potential consumer exposures from metofluthrin-containing products and available toxicology data.
https://oehha.ca.gov/media/downloads/crnr/101211metofluthrin.pdf 
 
University of Hertfordshire Pesticide Properties Database (PPDB). Metofluthrin Monograph. 
Summary: Independent pesticide database summarizing environmental fate, ecotoxicology, neurotoxicity concerns, persistence, and regulatory classifications.
https://sitem.herts.ac.uk/aeru/ppdb/en/Reports/1235.htm 
 
National Library of Medicine. PubChem Compound Summary: Metofluthrin. 
Summary: Chemical profile including structure, CAS number (240494-70-6), physicochemical properties, classification as a synthetic pyrethroid, and toxicological information.
https://pubchem.ncbi.nlm.nih.gov/compound/Metofluthrin 
 
Thermacell. Metofluthrin Ingredient Overview. 
Summary: Manufacturer description of metofluthrin technology, mechanism of action, and EP
https://www.thermacell.com/blog/metofluthrin-mosquito-repellent-ingredient 
 
Additional Clinical Perspective 
Bradman A, Castorina R, Boyd Barr D, et al. Determinants of Organophosphorus Pesticide Urinary Metabolite Levels in Young Children Living in an Agricultural Community. 
Summary: While not specific to metofluthrin, this and related pyrethroid biomonitoring literature provide context regarding human pesticide exposure and the growing interest in long-term neurodevelopmental effects of chronic pyrethroid exposure.
https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.5724 

Why "Thick Blood" Isn't the Whole Story

By Dr. Kristie Gering • February 16, 2026
Many people with chronic symptoms are told their labs are “normal,” yet they still feel unwell. One overlooked reason is excess fibrin , a sticky structural protein your body naturally makes to heal injuries. It’s what happens when too much fibrin builds up over time and/or when your body can't break it down fast enough. Think of fibrin like scaffolding In small amounts, fibrin helps healing In excess, it can: Form protective shells (biofilms) around bacteria or viruses Hide infections from antibiotics and the immune system Stiffen blood vessels Interfere with circulation and healing This can help explain why some infections or symptoms never fully go away . Why does fibrin build up? There are two main reasons: 1. Some people make too much fibrin This can be genetic or driven by chronic inflammation (infections, mold exposure, autoimmune conditions). 2. Some people don’t break fibrin down well Their bodies don’t activate the enzymes needed to dissolve excess fibrin. Many people have both problems at once. How this can affect health Excess fibrin has been linked to: Chronic or recurrent infections Long COVID symptoms Brain inflammation (PANS/PANDAS) Fatigue and pain syndromes Pregnancy loss Heart and blood vessel disease Importantly, standard clotting tests often don’t detect this because they’re designed for emergencies, not slow buildup over years. Why treatment must be gentle and personalized Breaking down fibrin too quickly can: Release trapped toxins or microbes Increase inflammation temporarily Make symptoms flare That’s why the goal is balance , not “thinning the blood.” When done correctly, fibrin support: Helps the immune system see hidden infections Improves response to other treatments Supports long-term healing rather than short-term suppression Key Takeaway If you’ve tried “everything” and still feel stuck, the issue may not be what you’re treating - rather w hat’s been blocking your body from clearing it. Excess fibrin may be that missing piece. Action Plan If you think this may apply to you: Request the Hypercoag Reflexive3 Panel (Labcorp Test Code: 505443) Set up an appointment with your provider to discuss the results. Resources for Further Information: https://www.betterhealthguy.com/episode207 https://canadarna.com/products/boluoke-lumbrokinase Episode #207: Hypercoagulation with Ruth Kriz, MSN, APRN - BetterHealthGuy.com After nearly thirty years since the start of a serious chronic illness, BetterHealthGuy.com chronicles my journey through and recovery from Lyme Disease, mold illness, and the myriad of issues chro...
NAD Drip, Chippewa Falls

Feeling tired? Try an NAD Infusion

December 1, 2023
Want help to get ready for the holidays? Having difficulty adjusting to the time change? Consider an NAD Infusion. What are the benefits? NAD+ (nicotinamide adenine dinucleotide) is a coenzyme that powers metabolic processes and impacts a wide variety of systems including digestion, cognition, mental clarity, aging, and overall energy levels. ​ NAD+ increases our body’s levels of serotonin, a neurotransmitter associated with mood regulation, and can improve symptoms of depression and anxiety. NAD+ plays a role in cell health and in hundreds of cell functions such as DNA repair, circadian rhythm, metabolism, muscle function, tissue repair and cognitive function. Basically, our cells require NAD+ to quickly shuttle around electrons - keeping the cells buzzing with the electricity of life! ​ Who is it for? NAD+ is the premier IV drip for clients who want to see major improvements in brain function, energy level, overcome anxiety and depression, handle acute and chronic stress more effectively, and cope better with PTSD. ​ What's inside? We administer 250mg or 500 mg of NAD+ in an IV drip. (We always start with 250mg the very first time you try it.) ​ How often? For best results, NAD+ may need several sessions depending on personal needs. The number of sessions will be discussed during an initial encounter. The NAD+ IV drip does take longer to receive than any other IV drip. Each session may last from 2.5 to 4 hours, depending on the tolerance. During the infusion, an individual might feel a bit of discomfort compared to standard vitamin drips - described as a bit of a rush through the body, but this is completely normal and can be controlled by how fast the IV is set to drip and stops within a minute or two after the drip ends. ​ Our NAD+ drip can be followed by Glutathione -"Master Antioxidant " - for best results. Fall 2023 Special - 250mg is $250 and 500mg is $350. Glutathione 1g added on after the infusion is $35.00.
DIM Evail

BRCA Gene & DIM Supplementation

October 30, 2023
Unfortunately, most of us know someone who has been affected by breast cancer. As of January 2022, here are some key facts about the prevalence of breast cancer in the United States: Common Cancer in Women: Breast cancer is the most common cancer among American women, aside from skin cancer. Incidence: In 2021, it was estimated that there would be over 281,000 new cases of invasive breast cancer in the United States. Additionally, there would be around 49,290 new cases of non-invasive breast cancer. Lifetime Risk: The American Cancer Society estimates that the lifetime risk of a woman developing breast cancer is about 13%, or 1 in 8. Mortality: In 2021, it was projected that approximately 43,600 women in the United States would die from breast cancer. Age and Breast Cancer: The risk of developing breast cancer increases with age. Most breast cancer cases are diagnosed in women aged 55 and older. Race and Ethnicity: Breast cancer incidence and mortality rates vary by race and ethnicity. White and African American women have the highest incidence rates, while African American women have a higher mortality rate. Screening and Early Detection: Mammography, thermography and regular breast self-exams are important tools for early detection. The earlier breast cancer is detected, the more treatment options are available, and the better the chances of survival. Survival Rates: Survival rates for breast cancer have been improving over the years, in part due to early detection and advances in treatment. The 5-year relative survival rate for localized breast cancer is close to 100%. Genetic Factors: Some individuals, particularly those with a family history of breast cancer or certain genetic mutations (e.g., BRCA1 and BRCA2), have a higher risk of developing breast cancer. Preventive Measures: Lifestyle factors such as maintaining a healthy weight, regular physical activity, limited alcohol consumption, and avoiding smoking are associated with a reduced risk of developing breast cancer. As mentioned above, the BRCA gene mutation is associated with a significantly increased risk of developing breast and ovarian cancer. For those who carry this genetic mutation, the need for effective preventive measures and early detection strategies is of paramount importance. Recent research has shed light on the potential role of DIM, a natural compound found in cruciferous vegetables, in this context. ​ Diindolylmethane is a bioactive compound that has garnered attention for its health-promoting properties, particularly in cancer prevention. Our growing understanding of DIM's mechanisms and its impact on individuals with the BRCA gene mutation has opened new avenues of exploration. Here are some key aspects of how DIM could potentially benefit healthy BRCA gene carriers: Modulation of Estrogen Metabolism: DIM has been shown to influence the metabolism of estrogen, a hormone that plays a crucial role in breast cancer development. By favoring the production of a less potent and potentially less harmful form of estrogen, DIM may help reduce the cancer-promoting effects of this hormone. Regulation of BRCA Gene Expression: Emerging research suggests that DIM might influence the expression of the BRCA genes themselves. This could have a significant impact on the way these genes function and interact with cancer development pathways. Reduction of Breast Density: High breast density is associated with an increased risk of breast cancer and can also make it more challenging to detect tumors via traditional screening methods. Preliminary studies indicate that DIM may contribute to a decrease in breast density, potentially improving the effectiveness of breast cancer screening for BRCA gene carriers. There's a study that utilized DFH's DIM-Evail formula at the time. It has since been reformulated to be even more bioavailable! Pretty cool information and definitely a step in the right direction! ​ This study investigated the effect of DIM supplementation on breast density, a recognized predictive factor of breast cancer risk. Participants were 23 healthy female BRCA carriers, with the majority being post-menopausal. They were treated with oral DIM 100 mg × 1/day for 1 year. The amount of fibroglandular tissue (FGT) and background parenchymal enhancement (BPE) on magnetic resonance imaging (MRI) performed before and after the intervention was scored by two independent expert radiologists using the Breast Imaging and Reporting Data System. The results showed a decrease in the average score for FGT with no significant change in BPE. A group of DIM-untreated (age and menopausal status matched women) from the BRCA clinic did not show a significant change in FGT amount in a parallel year. . In conclusion, 1 year’s supplementation with DIM 100 mg × 1/day in BRCA carriers was associated with a significant decline in FGT amount on MRI. Interestingly, besides certain gene mutations, there are many other variables that have been shown to increase the risk for breast cancer. These include: · Mold Toxicity/Exposure · Radiation Exposure · Breast Implants · Heavy Metals (Including Amalgam Fillings) · Dental Infections · Toxins such as BPA, PFAS/PFOAs · Phthalates