The Tick-ing Time Bomb: Repellents, Regulation, and a Growing Public Health Challenge

Ticks have long been an unwelcome consequence of spending time outdoors, but the public health significance of tick exposure is becoming difficult to ignore. Changes in the geographic distribution of tick species, longer periods of seasonal activity in some regions, changing land-use patterns, movement of wildlife hosts, and increased human exposure to tick habitats make the risk of tick-borne disease an increasingly important public health issue in the United States and elsewhere.

In the United States, Lyme disease, an illness caused by borrelia bacteria, remains the most commonly reported insect vector-borne disease. More than 89,000 cases were reported to the U.S. Centers for Disease Control and Prevention (CDC) in 2023, although CDC estimates that approximately 476,000 people may be diagnosed and treated for Lyme disease annually. The national surveillance case definition for Lyme disease was modified in 1996, 2008, 2011, 2017, and again in 2022. Some of these changes impacted surveillance data and must be considered when attempting to interpret trends, as there is no way to compare directly Lyme disease rates prior to 2022. The available data nonetheless demonstrate that there is an overall increase in cases since 2008. Lyme disease is only one component of the problem. Ticks in the United States can transmit pathogens responsible for anaplasmosis, babesiosis, ehrlichiosis, Rocky Mountain spotted fever (RMSF) and other spotted-fever rickettsioses, Powassan virus disease, and other illnesses. CDC reports that the number of people in the United States affected by Alpha-gal syndrome (AGS), a potentially life-threatening allergy from a tick bite, may be as high as 450,000.

Not every tick poses the same risk, however. Of the many tick species found worldwide, relatively few routinely bite humans and transmit human pathogens. In the United States, species of particular public health significance include the blacklegged tick (Ixodes scapularis), western blacklegged tick (Ixodes pacificus), lone star tick (Amblyomma americanum), American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni), Gulf Coast tick (Amblyomma maculatum), and brown dog tick (Rhipicephalus sanguineus). The public health concern extends well beyond any single tick species, disease, or region.

Climate, Ecology, and Human Exposure

Climate change is one important component of this changing risk landscape, although the relationship between climate and tick-borne disease is complex. Temperature and moisture affect tick survival, development, activity, and geographic suitability. Warmer conditions can extend the periods during which ticks are active and allow some species to survive in areas that historically were less suitable. Canadian authorities, for example, expressly identify climate change as contributing to increases in tick abundance, longer periods of tick activity, expansion of suitable habitat, and longer seasons during which people may be exposed.

Climate, however, does not operate in isolation. Tick distribution and disease incidence also depend on land use, vegetation, populations and movement of host species such as deer, rodents, and birds, pathogen prevalence within those hosts, and human behavior. Changes in outdoor recreation and residential development near wooded or brushy habitat can increase opportunities for human-tick encounters even without a corresponding change in tick abundance. Increased tick surveillance and awareness of tick-borne diseases also contribute to higher reported disease numbers. The result is better understood as a convergence of environmental, ecological, and behavioral factors than as a simple climate-driven expansion. That distinction matters for public health policy because no single intervention can eliminate tick exposure.

Ticks on the Move

In the United States, tick-borne disease risk varies considerably by region and species. Lyme disease risk remains particularly concentrated in the Northeast, mid-Atlantic, and upper Midwest, with a separate western focus associated with the western blacklegged tick. Other medically important ticks occupy different and sometimes overlapping ranges.

Tick distributions are not static. The lone star tick, for example, has historically been associated with the southeastern and south-central United States but is now encountered farther north, while the brown dog tick occurs worldwide. The blacklegged tick is now broadly distributed across the eastern United States, while other species historically associated with particular regions have been documented outside their traditional ranges. An additional concern is the arrival of non-native species. The Asian longhorned tick (Haemaphysalis longicornis), first reported in the United States in 2017, has now been found in numerous eastern and midwestern states. Although it currently appears less attracted to humans than several native species, establishment of the Asian longhorned tick in the United States illustrates how quickly the vector landscape can change.

Canada’s blacklegged tick risk areas have expanded across portions of Manitoba, Ontario, Quebec, and the Maritime provinces, while western blacklegged ticks occur in British Columbia. Canadian public health authorities report expanding blacklegged tick habitat and an increasing incidence of Lyme disease. Canada reported an incidence rate of 14.1 Lyme disease cases per 100,000 people in 2024, compared with 11.9 per 100,000 in 2023.

This is not solely a North American phenomenon; similar geographic shifts are being observed elsewhere. European authorities continue to monitor changes in tick distribution, including Ixodes ricinus, an important vector of Lyme borreliosis and tick-borne encephalitis whose distribution has shifted toward higher latitudes and elevations in portions of Europe. I. ricinus occurs across a vast area extending from the Mediterranean region into Scandinavia, and European public health authorities continue to update vector-distribution maps as surveillance identifies changes in tick populations.

The practical implication is that historical assumptions about where tick precautions are necessary are becoming less reliable. Consumers, public health agencies, pesticide regulators, and product manufacturers increasingly must account for changing patterns of exposure.

Layers of Protection

There is no single method of preventing tick bites. Public health authorities instead recommend layered protection. Behavioral measures include avoiding high grass and brush where possible, staying toward the center of trails, and checking people, pets, clothing, and gear after potential exposure. Physical barriers such as long trousers, long sleeves, closed footwear, and clothing arrangements that limit access to skin can provide another layer of protection.

Once an attached tick is discovered, CDC recommends removing it as soon as possible. Using clean, fine-tipped tweezers, the tick should be grasped as close to the skin’s surface as possible and pulled away with steady, even pressure. Avoid squeezing the tick to avoid or reduce transfer of any pathogenic material from the tick. Tick removal itself falls largely outside the pesticide regulatory questions addressed in this memorandum, but it underscores an important point: effective protection against tick-borne disease involves a continuum of interventions. Avoidance, protective clothing, post-exposure tick checks, and prompt removal each play a role.

Chemical repellents and insecticides add another important layer in the larger public health strategy. CDC recommends U.S. Environmental Protection Agency (EPA)-registered skin-applied repellents containing active ingredients such as DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanone and recommends products containing 0.5 percent permethrin for treating clothing and gear. Permethrin products intended for clothing should not be applied directly to skin. Anyone using these products should note that permethrin is toxic to cats and some white-footed dogs. Pesticidal products should always be used according to their labels, and users should note that not all insect repellents are equally effective.

These distinctions illustrate an important feature of the repellent marketplace: products that consumers may colloquially group together as “tick repellents” can operate differently, contain different active ingredients, target different organisms, and may be subject to different regulatory requirements. As discussed below, whether and how a product is regulated under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) can therefore have significant consequences for the evidence supporting the claims consumers see on the label.

Pesticide Regulation in the United States

Under FIFRA, EPA has primary authority to register pesticides in the United States. A pesticide, except in limited circumstances, must be registered before it can be sold or distributed in the United States. The EPA definition of a “pesticide” is much broader than the average consumer may be aware; in general, a pesticide is any product that prevents, destroys, repels, or mitigates a pest. The term “pest” also has a broad meaning, encompassing any living organism (e.g., rodents, insects, bacteria, or viruses) that are unwanted and may cause damage to human health, crops, or animals.

The process of pesticide registration can be lengthy and costly. EPA must first approve all the ingredients in a pesticide product, not only those that provide the pesticidal action but also the other, or “inert,” ingredients (e.g., solvents, carriers, propellants). It is the responsibility of the registrant to provide proof to EPA that when the product is used as directed, it will not pose a risk to humans or the environment — this typically comes in the form of laboratory data and sometimes elaborate field studies.

Pesticides that are registered by EPA for application to human skin, such as insect repellents (e.g., lotions, sprays, wipes), require a significant amount of data. EPA also requires product chemistry, safety, and efficacy data for outdoor spatial insect repellents (e.g., lanterns, torches, candles) or clip-on products that are for use near human bodies. Interestingly, EPA does not require registration for pest control devices (e.g., ultrasonic or sound wave repellers, light traps). The efficacy of such devices may be uncertain, but if there is a question regarding the validity of a device’s label claims, EPA can, under FIFRA, require that the device producer provide proof of efficacy.

Pesticide label claims must be approved by EPA; in fact, the approved label is the culmination of the registration process. It is a violation of federal law to use the product in a manner not consistent with its approved label. When a product label includes claims that it may in some way protect human health, then product performance data are required to ensure its efficacy. Mosquitoes and ticks are designated as public health pests and therefore product label claims to protect against, or repel, mosquitoes and ticks are considered public health claims.

An issue surrounding mosquito and tick repellents for many years is the inherently reduced requirements for those products that meet the criteria of Minimum Risk Pesticides, known as 25(b) products. Under Section 25(b) of FIFRA, certain “minimum risk” pesticides are exempt from federal registration requirements because EPA has determined that their ingredients pose little to no hazard to humans or the environment. Although these products do not require federal registration, they are required to be registered in most states. Conditions of registration vary greatly state-to-state — from application costs to data requirements.

A 25(b) product, as defined under FIFRA, cannot make public health claims that link the target pests with any specific disease (e.g., RMSF), but when registered by the states, the product labels may include general repellency claims (i.e., repels ticks). The longstanding concern, and basis for the Consumer Specialty Products Association’s (CSPA) petition to EPA in 2006, is that consumers will not appreciate this nuanced distinction and therefore will expect the same level of efficacy, and safety, from the 25(b) products. Although there is some alignment across states that require efficacy data for 25(b) repellent products, the test standards are far below what is required by EPA for federal registrations. It is noteworthy that CDC’s recommendations regarding topical insect repellents include only products containing EPA-registered active ingredients.

Testing Requirements

While consumers may consider such factors as cost and aesthetics (smell and feel) in their selection of a skin-applied insect repellent product, their decision may be biased by uninformed assumptions about toxicity and effectiveness. Registration of skin-applied repellent products in the United States under FIFRA is predicated on EPA’s evaluation and approval for human safety and effectiveness when used according to instructions on the label, and assures that the product does not pose risks to vulnerable populations, including children and pregnant women. This rigorous regulatory evaluation is based on comprehensive data developed for the product as formulated for use and its active ingredients according to harmonized test guidelines and Good Laboratory Practice (GLP) Standards. Core data requirements include basic product chemistry, human health hazard (dermal irritation, sensitization, and other toxicity endpoints following acute, prolonged, and/or repeated exposure), and product performance (efficacy). Data from acute toxicity studies serve as a basis for classification and precautionary labeling to limit exposure and/or potential adverse effects.

When an insect repellent label includes “public health claims” — claims of protection against certain diseases — EPA requires that in addition to the baseline testing, efficacy must be demonstrated on the vector species that is known to carry that disease. Each applicant must demonstrate through testing that their skin-applied insect repellent product is efficacious when used in accordance with label directions to support the pest-specific claims listed therein. For instance, to support a label claim to “protect against ticks that transmit Rocky Mountain spotted fever),” a registrant would need to submit efficacy data on the Rocky Mountain wood tick in addition to the Blacklegged tick and the Lone Star tick as required for general repellency claims against ticks (note, there are other tick species that carry the bacterium Rickettsia rickettsii that causes RMSF that could be used for testing).

The effectiveness of insect repellents is determined by a calculated Complete Protection Time (CPT), i.e., the time from application of a skin-applied insect repellent until efficacy failure, which is described in Product Performance Test Guideline 810.3700. For skin-applied insect repellent labeling claims, the performance standard under FIFRA Data Requirements at 40 C.F.R. Part 158 is a CPT of greater than or equal to two hours without reapplication. Claims of longer protection times must be supported with data.

Failure of repellency, from which CPT is derived, is not based on the number of bites. In a controlled, laboratory tick efficacy study, for example, the key endpoint is tick crossings — the act of passage by a tick from an area of untreated skin to an area of treated skin on a human arm; for mosquito efficacy testing in the field or laboratory, the key endpoint is landings. The human subjects involved in the testing nonetheless must consent to being exposed voluntarily to the biting pest(s) for which a repellency claim will be made, as there remains an inherent risk of bite during testing. A representative population of animals involved in the efficacy testing for skin-applied insect repellents therefore must be pre-screened for vector diseases to assess and mitigate the potential risk of the human subjects and personnel in the study being exposed to pathogens, regardless of whether the exposures will occur in the field or laboratory. Tick efficacy studies are conducted using disease-free laboratory colonies at the appropriate life stage of the species that the product label claims to repel; two species may be tested concurrently in one study. Tick species commonly tested in the United States include the blacklegged tick (deer tick, Ixodes scapularis), western blacklegged tick (deer tick, Ixodes pacificus), lone star tick (Amblyomma americanum), American dog tick (Dermacentor variabilis), brown dog tick (Rhipicephalus sanguineous), and relapsing fever tick (softbacked tick, Ornithodoros turicata).

Unlike observational exposure monitoring studies in human populations (occupational or consumer), efficacy testing for skin-applied insect repellents also involves intentional exposure of human subjects to the product subject to FIFRA registration. The administered dose of the product in these studies is informed by a risk determination based on the toxicity of the product components and established standard consumer application rates for the type of product tested.

Efficacy studies involving human subjects conducted in the United States must meet the requirements under 40 C.F.R. Part 26, Subparts K, L, and M, including comprehensive technical (scientific and statistics) and ethics reviews and approval of testing protocols by EPA, EPA’s Human Studies Review Board (HSRB), Institutional Review Board (IRB), and, if applicable, the state regulatory authority where testing will be performed, prior to study initiation. The proposed protocol and supporting documentation are submitted to EPA under Pesticide Registration Improvement Act of 2022 (PRIA 5; Table 19, Code M001) for EPA/HSRB review. Upon study completion, EPA and HSRB also must review the final study report and all supporting documentation (e.g., consent materials, data, and internal IRB records), which are submitted under PRIA 5 (Table 19, Code M002).

Registration of insect repellents in the United States is not for the faint of heart. While EPA is currently reassessing and taking measures to streamline the regulatory review process, factors external to EPA’s process can add to protracted timelines — the registrant’s capital funding, laboratory capabilities and capacity, and discordance between testing and review cycles. Registrants can expect just the product performance evaluation to add as much as two to five years to the regulatory approval timeline (longer if there are additional claims or there is disagreement in CPT) and an additional $25,000 in regulatory (PRIA) fees for each efficacy study submitted. Contrary to EPA estimates, tick efficacy testing costs can exceed $300,000 depending on the number of pest-specific claims and, thus, the number and complexity of efficacy studies that must be performed; by comparison, field efficacy testing for mosquito repellent claims can reach $1 million. There are few testing facilities throughout the United States that have not only the technical expertise for study conduct according to Test Guideline 810.3700, but also compliance with GLP Standards and the experience and fortitude to navigate a multi-year review and consent process.

Though laboratory-performed tick repellency studies are not constrained by the geographic and seasonal limitations of field testing required for mosquito and biting fly repellency claims, they are beholden to the EPA-HSRB review cycle. There are a limited number of studies, of which skin-applied insect repellents studies are a small fraction, that the HSRB can practicably review during each quarterly meeting. It is noteworthy that the 25(b) repellent products, even those registered in states that require efficacy data, do not have to meet any GLP testing requirements or undergo the rigorous EPA, HSRB, and IRB review and approval processes. The unique and arduous process to assess efficacy and register a skin-applied insect repellent can stifle innovation and delay products getting to market. Many repellent product formulators therefore may be reluctant to attempt to enter into the U.S. market unless they meet the criteria for a 25(b) exemption from federal regulation under FIFRA Section 25(b).

To ensure the product efficacy aligns with the expected performance and label use conditions, consumers should consider whether they need protection from ticks and/or other biting insects, the expected period of exposure, and the potential need for reapplication. A product’s CPT may vary by taxa or species and, based on available human health risk information, product labels may specify a maximum number or reapplications in a day. Application rates of registered products are informed by margins of exposure that are derived during the registration process based on toxicity data; dose and/or frequency of product use may be restricted to balance potential risk with efficacy. If conditions of outdoor activities result in anticipated removal of the product from the skin and/or diminished efficacy (e.g., physical activity/perspiration, water exposure, or air temperature), reapplication may be required at a frequency different from other protective skincare (e.g., sunscreen) products that may also be in use. CDC therefore advises against combined products and recommends instead separate application of sunscreen and then insect repellent.

Global Strategies — Repellents beyond FIFRA

The expanding public health importance of ticks is not unique to the United States, nor is the regulatory challenge of ensuring that products marketed to prevent bites are both safe and effective. Other jurisdictions have developed regulatory frameworks that, like FIFRA, treat claims of disease vector repellency as more than ordinary consumer product claims.

European Union

In the European Union (EU), insect and tick repellents are generally regulated under the Biocidal Products Regulation (BPR). Repellents and attractants fall within Product Type 19 (PT19), which includes products used to repel harmful organisms and those used expressly for human or veterinary hygiene, either directly on the skin or indirectly in the surrounding environment.

The BPR employs a two-stage structure under which active substances are evaluated and approved, and biocidal products containing those substances must generally be authorized before being placed on the market. Depending upon the intended market, applicants may pursue national authorization, mutual recognition across member states, or, for qualifying products, Union authorization. PT19 products are eligible for Union authorization.

Efficacy is part of the authorization inquiry, and the resulting authorization can be highly specific as to target organism, application rate, frequency, user population, and claimed duration of protection. Authorized PT19 products, for example, may distinguish between the duration of protection against mosquitoes and protection against ticks rather than allowing a generalized “insect repellent” claim. That structure shares a fundamental premise with FIFRA: a product’s claimed ability to repel a public-health pest is a claim that regulators expect to be supported rather than simply accepted as marketing language.

Canada

Canada likewise regulates personal insect repellents as pest control products. Health Canada’s Pest Management Regulatory Agency (PMRA) evaluates products for safety and effectiveness before they may be sold for pesticidal uses. Health Canada expressly advises consumers that only government-approved products may be sold with claims that they protect against biting insects.

Approved Canadian personal repellents include products containing DEET, icaridin (known as picaridin in the United States), permethrin, soybean oil, metofluthrin, and p-menthane-3,8-diol/oil of lemon eucalyptus, among other ingredients. Permitted uses and restrictions vary by active ingredient, concentration, and population. Canada also regulates insecticide-treated clothing, including clothing treated with permethrin for protection against mosquitoes and ticks.

Canada provides an especially useful example of the intersection between regulation and changing vector risk. Canadian public health authorities specifically identify climate change as one contributor to the expansion of blacklegged tick habitat and increasing human exposure to ticks and tick-borne pathogens. As the geographic areas in which consumers may need effective tick protection expands, the availability and performance of regulated repellent products takes on corresponding public health significance.

United Kingdom

Great Britain regulates repellents under the Great Britain Biocidal Products Regulation (GB BPR), while Northern Ireland remains subject to the EU BPR. Like the EU framework, the GB BPR classifies repellents and attractants as PT19 biocidal products. Products that control organisms solely through physical means generally fall outside the biocides framework, while products relying upon a chemical or biological mode of action may require authorization.

The British framework also illustrates the close connection between efficacy claims and regulatory status. The Health and Safety Executive (HSE) maintains efficacy guidance specifically addressing PT19 products and requires applicants to provide data supporting relevant product claims. Advertising requirements further prohibit misleading descriptions of biocidal products.

Different Regulatory Frameworks, Similar Questions

The legislative and enforcement details differ substantially among FIFRA, EU BPR, GB BPR, and Canada’s pest-control frameworks, authorization procedures, labeling requirements, data requirements, the time, expense, and approval process associated with bringing products to market, and the penalties for not meeting the minimum standards or making false or unsupported claims. The systems nevertheless confront remarkably similar questions: What organism(s) does the product repel? How long does the claimed protection last? Under what conditions was that protection demonstrated? Is the product safe for its intended users and manner of application? does the label accurately communicate those limitations?

These questions are becoming more consequential as tick populations and human exposure change. A repellent is ultimately a public health tool for which its value depends not simply on whether and where it can be purchased, but on whether consumers understand what it does, how long it works, and how it must be used to provide the protection claimed. In the United States, FIFRA provides the principal regulatory framework for answering these questions.

Bergeson & Campbell, P.C. (B&C^®) publishes blogs and memoranda on key issues facing the chemical regulated industry. Later in September, B&C will publish further insight on products exempted under FIFRA Section 25(b) in B&C’s FIFRA Blog®. Subscribe here.