Why Are So Many People Getting Lyme Disease?

Lyme disease risk is changing
Ticks are expanding into new areas
Environment, exposure, and surveillance all matter

Why are so many people getting Lyme disease? There is no single explanation. Blacklegged ticks have expanded into new geographic areas, environmental conditions can influence tick survival and activity, changing landscapes affect ticks and their animal hosts, and people increasingly live and spend time where infected ticks are present.

At the same time, increases in reported Lyme disease cases do not always mean infections increased by exactly the same amount. Changes in surveillance definitions, reporting practices, awareness, and diagnosis can also affect the numbers.

The Centers for Disease Control and Prevention reports more than 80,000 Lyme disease cases through national surveillance each year. A separate estimate based on insurance claims suggests that approximately 476,000 people may be diagnosed and treated for Lyme disease annually in the United States, although the CDC cautions that this estimate may include some people treated on clinical suspicion who do not actually have Lyme disease.

The larger picture is therefore more complicated than simply saying there are “more ticks.” Lyme disease risk reflects an interaction among ticks, Borrelia, animal hosts, habitat, weather and climate, human behavior, and how cases are detected and counted.

Is Lyme Disease Really Becoming More Common?

There is evidence that Lyme disease risk has expanded geographically in parts of the United States, particularly as populations of the blacklegged tick, Ixodes scapularis, have become established in additional areas.

Eisen and Eisen reviewed the historical distribution of the blacklegged tick and found documented expansion in the Northeast, Upper Midwest, and Ohio Valley. In areas where expanding tick populations were accompanied by Borrelia burgdorferi in host-seeking ticks, increases in human Lyme disease cases followed.

However, surveillance has also improved substantially. Researchers therefore have to distinguish between a tick population truly moving into a new area and a population that was already present but had not previously been recognized or systematically documented.

This distinction matters. Rising case counts can reflect a combination of genuine changes in disease risk and changes in how well that risk is measured.

Are Ticks Spreading Into New Areas?

Yes. The geographic range of the blacklegged tick has changed substantially over time.

Ixodes scapularis is now widely distributed across the eastern United States. Researchers have documented expansion of established populations in parts of the Northeast, Upper Midwest, Ohio Valley, and portions of the Southeast.

This does not mean that every tick in these areas carries Borrelia burgdorferi or that every tick bite leads to Lyme disease. Risk depends on whether the tick species can transmit Lyme disease, whether the tick is infected, and whether transmission occurs during feeding.

Geography also remains important. The CDC identifies the Northeast, mid-Atlantic, and upper Midwest as the major U.S. regions for Lyme disease.

Patients may not realize they were exposed. Nymphal blacklegged ticks are extremely small and their bites can go unnoticed. This is why a patient can develop Lyme disease without remembering a tick bite.

Why Is Lyme Disease More Common in the Northeast?

Lyme disease risk is not determined simply by whether blacklegged ticks are present. The ecology and behavior of ticks, the animals they feed on, the prevalence of Borrelia in host-seeking ticks, the landscape, and human exposure all influence risk.

In northern areas of the eastern United States, nymphal blacklegged ticks commonly seek hosts in ways that bring them into contact with people. Nymphs are particularly important because they are small, can be difficult to detect, and are responsible for many human exposures.

Forest environments and the edges between wooded and residential areas can also provide suitable habitat for ticks and their hosts. As a result, exposure does not require a wilderness hike. It can occur while gardening, walking a dog, playing outside, working around a property, or spending time near wooded edges.

Do Deer and Mice Explain the Increase in Lyme Disease?

Animal hosts are an important part of Lyme disease ecology, but the familiar explanation that Lyme disease is simply caused by “too many deer” is incomplete.

Adult blacklegged ticks frequently feed on white-tailed deer, which are important reproductive hosts for the tick. Immature ticks feed on many different vertebrates, including small mammals and birds. Some of these animals can also serve as reservoirs for Borrelia burgdorferi.

Changes in deer populations, small-mammal communities, predators, vegetation, and habitat can therefore alter the ecological system that supports ticks and Borrelia.

Researchers continue to debate the relative importance of individual hosts. A major review of Lyme disease ecology identified the precise relationship between deer abundance, tick abundance, host communities, and infection risk as an area where important uncertainty remains.

Does Climate Change Increase Lyme Disease Risk?

Climate can influence ticks, but climate alone does not explain Lyme disease trends.

Ticks are affected by temperature, humidity, precipitation, and seasonal conditions. Warmer conditions can influence tick survival, development, geographic suitability, and the length of time during which ticks can be active.

A systematic review of 84 U.S. studies found that climate, seasonality, land use, and other environmental factors all influence the epidemiology of major tick-borne diseases. The authors emphasized that these relationships vary by region and that more localized research is needed.

Historical research on blacklegged ticks also suggests that reforestation, recovery of deer populations, and more recent climate warming have all contributed to the proliferation and geographic spread of Ixodes scapularis.

It is therefore more accurate to view climate as one part of a larger ecological system rather than as the sole explanation for rising Lyme disease risk.

Does Land Use Affect Lyme Disease Risk?

Yes. The way people alter and use landscapes can affect where ticks and their animal hosts thrive and where humans encounter them.

Historical deforestation dramatically changed wildlife and tick habitat in the eastern United States. Later reforestation, changes in wildlife populations, suburban development, and fragmented wooded landscapes created a different ecological setting.

Today, many people live where lawns, yards, trails, parks, and neighborhoods meet wooded habitat. That creates opportunities for contact between people and ticks without requiring prolonged travel into remote forests.

Reviews of Lyme disease ecology have identified land use, land cover, forest fragmentation, vegetation, host communities, climate, and human behavior as interacting influences on Lyme disease risk.

Are People Getting Lyme Disease Around Their Homes?

Tick exposure can occur close to home. Blacklegged ticks may be found in wooded, brushy, grassy, and leaf-litter environments, including the edges of residential properties.

Routine activities such as gardening, yard work, walking pets, playing outside, and moving between lawns and wooded areas can create opportunities for exposure.

This is one reason prevention cannot focus only on hiking and camping. A broader Lyme disease prevention strategy includes environmental awareness, protective clothing, repellents when appropriate, tick checks, prompt tick removal, and recognition of early symptoms.

Are More Lyme Disease Cases Being Diagnosed Because Awareness Is Better?

Greater awareness and surveillance can contribute to increases in reported Lyme disease cases, but they do not fully explain the geographic expansion of risk.

Lyme disease has been nationally notifiable in the United States since 1991. Public health surveillance depends on case definitions and reporting systems, and those systems change over time.

A major change occurred with the 2022 surveillance case definition. The CDC notes that changes in how cases are classified and reported must be considered when comparing case counts over time.

This produced a particularly visible jump in reported cases. Mayo Clinic reported that U.S. Lyme disease case counts rose 68.5% after the revised surveillance definition took effect.

That increase should not be interpreted as evidence that Lyme infections suddenly rose 68.5% in a single year. Part of the increase reflected how cases were counted.

At the same time, improved reporting cannot explain away the documented expansion of blacklegged tick populations and Lyme disease risk into new geographic areas.

Why Can Lyme Disease Still Be Missed If It Is So Common?

A disease can be common in an endemic area and still be difficult to recognize in an individual patient.

Patients may never notice the tick. An erythema migrans rash may not be recognized. Early antibody testing can be negative before a detectable immune response develops. Symptoms such as fatigue, headache, joint pain, dizziness, facial weakness, numbness, or cognitive difficulties may initially suggest other conditions.

Geography can also complicate recognition when clinicians or patients underestimate exposure risk in an area where ticks have recently become established.

The expanding geographic range of ticks therefore has a clinical implication: physicians may encounter Lyme disease in locations where it was considered uncommon in the past.

Does More Lyme Disease Mean Everyone Outdoors Is at High Risk?

No. Lyme disease risk varies substantially by location, season, habitat, tick abundance, infection prevalence, and individual exposure.

Spending time outdoors does not mean someone will develop Lyme disease. Likewise, living outside a traditionally recognized Lyme disease hotspot does not guarantee that exposure cannot occur.

The practical goal is not to avoid outdoor activity. It is to understand local risk and reduce opportunities for tick attachment.

Preventive measures can reduce exposure, although no strategy eliminates every tick bite. If an attached tick is found, the next question becomes what can stop Lyme disease before or after infection develops.

Frequently Asked Questions

Why are so many people getting Lyme disease?

There is no single cause. Blacklegged ticks have expanded into new areas, while climate, land use, animal hosts, suburban and recreational exposure, human behavior, awareness, and surveillance all influence the number of Lyme disease cases that occur or are reported.

Why is Lyme disease so common now?

Lyme disease risk has expanded geographically in parts of the United States as blacklegged ticks have become established in additional areas. Environmental conditions, changing landscapes, host populations, human exposure, improved recognition, and changes in surveillance also contribute to the numbers being reported.

Are Lyme disease cases actually increasing?

Lyme disease risk has genuinely expanded in some geographic areas, but reported case counts are also affected by surveillance and reporting changes. The 2022 U.S. surveillance definition substantially changed how cases were counted, so increases in reported cases should not automatically be interpreted as equivalent increases in new infections.

Are ticks spreading into new areas?

Yes. Research has documented expansion of established blacklegged tick populations in the Northeast, Upper Midwest, Ohio Valley, and other areas. In several locations, establishment of infected tick populations has been followed by increases in human Lyme disease cases.

Does climate change cause more Lyme disease?

Climate can affect tick survival, activity, development, and geographic suitability, but it is not the only factor influencing Lyme disease. Land use, habitat, animal hosts, tick behavior, human exposure, and surveillance also matter, and their relative importance varies by region.

Why is Lyme disease more common in the Northeast?

The Northeast has ecological conditions that support blacklegged ticks, animal hosts, and transmission of Borrelia burgdorferi. Nymphal ticks in northern populations also commonly seek hosts in ways that increase opportunities for human contact. Lyme disease risk nevertheless varies considerably even within the Northeast.

Can you get Lyme disease in your own yard?

Yes. Tick exposure can occur around homes, particularly near wooded edges, brush, leaf litter, and other suitable tick habitat. Gardening, yard work, playing outdoors, and walking pets can all create opportunities for exposure.

How many people get Lyme disease each year?

The CDC reports more than 80,000 Lyme disease cases through national surveillance each year. A separate estimate based on insurance claims suggests that approximately 476,000 people may be diagnosed and treated for Lyme disease annually in the United States, although that estimate may include some people treated on clinical suspicion who do not actually have Lyme disease.

Clinical Takeaway

More people appear to be getting Lyme disease because several forces are operating at the same time. Blacklegged ticks have expanded geographically, landscapes and animal populations have changed, environmental conditions affect tick survival and activity, and people frequently encounter ticks around homes and during ordinary outdoor activities.

At the same time, surveillance and reporting have changed. Rising reported case counts therefore should not be interpreted as a perfect measure of how much infection itself has increased.

The most useful clinical perspective is to recognize that Lyme disease risk is dynamic. A location considered low risk years ago may not carry the same risk today, and the absence of a remembered tick bite does not exclude exposure.

Lyme disease is becoming a concern in more places because the ecology of ticks, hosts, habitat, climate, and human exposure is changing—and our ability to recognize and count cases is changing with it.

Related Articles

These articles explore tick exposure, prevention, and what to do when a tick bite occurs:

Should You Save the Tick After a Tick Bite?
What to Do After a Tick Bite: Wait or Treat?
Can Lyme Disease Go Away on Its Own?
Can One Dose of Doxycycline Prevent Lyme Disease?

References

1. Centers for Disease Control and Prevention. Lyme Disease Surveillance and Data. Lyme Disease. Updated September 9, 2026.
2. Centers for Disease Control and Prevention. Preventing Lyme Disease. Lyme Disease. Updated May 21, 2026.
3. Eisen L, Eisen RJ. Changes in the geographic distribution of the blacklegged tick, Ixodes scapularis, in the United States. Ticks Tick Borne Dis. 2023;14(6):102233. doi:10.1016/j.ttbdis.2023.102233.
4. Deshpande G, Beetch JE, Heller JG, Naqvi OH, Kuhn KG. Assessing the Influence of Climate Change and Environmental Factors on the Top Tick-Borne Diseases in the United States: A Systematic Review. Microorganisms. 2024;12(1):50. doi:10.3390/microorganisms12010050.
5. Kilpatrick AM, Dobson ADM, Levi T, et al. Lyme disease ecology in a changing world: consensus, uncertainty and critical gaps for improving control. Philos Trans R Soc Lond B Biol Sci. 2017;372(1722):20160117. doi:10.1098/rstb.2016.0117.

Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention