A tick on clothing for an article on Lyme disease

Lyme disease is the most common insect-borne disease in the U.S., by far. The Centers for Disease Control and Prevention logs 30,000 cases every year, and the agency believes that tenfold more go unreported.

Given how common the disease is, you’d think that doctors and scientists would agree on the basics,  such as how best to diagnose and treat it, and whether it can turn into a chronic condition.

But it turns out that when it comes to Lyme, there are still a lot of unknowns and plenty of debate.

“There is definitely some confusion and also some misinformation out there,” says Amy Schwartz, an epidemiologist at the CDC. “And it’s important to correct that, because without proper treatment, the condition can be devastating.”

Here’s a breakdown of what scientists do and don’t know about this dangerous and increasingly common illness.

How Lyme Disease Spreads

Lyme disease is spread by a bacteria known as Borrelia burgdorferi, which is transmitted to humans, household pets, and forest critters (including mice and deer) via the blacklegged tick (sometimes referred to as the deer tick). The CDC and the Infectious Disease Society of America (IDSA) both agree that the tick has to remain attached for 24 to 48 hours in order to transmit the Lyme-causing bacteria.

The disease is most common in late spring and early summer, when young (poppy-seed-size) ticks are active, and when people tend to spend more time outdoors.

Schwartz says both the tick and the diseases it carries are still most common in the Northeast, Mid-Atlantic, and North Central U.S.  “About 95 percent of Lyme cases still come from 14 states, all located within those regions,” she says. “But the number of counties within those states that we consider high risk for Lyme disease has gone up by more than 300 percent.”

Despite what you might read online, the vast majority of scientists agree that getting bitten by a blacklegged tick is really the only way to contract Lyme disease: You can’t catch it from sex, from eating deer meat, or from any tick except the blacklegged kind. You also can’t catch it directly from your pets or any other forest creatures; only ticks can transmit the disease to humans.

How to Protect Yourself

The good news is that you can take several steps to reduce your risk of being bitten by an infected tick in the first place. Here's how:  

  • If you can, avoid areas with ticks, particularly during peak tick season (late spring to early fall). These include wooded and brushy areas with high grasses and leaf litter.

  • When spending time in a tick-infested area, dress carefully. Wear long sleeves, long pants, and long socks. Light colors are best because you can spot ticks more easily. To be extra safe, tuck your pants into your socks and your shirt into your pants.

  • Apply an effective insect repellent to your clothes and exposed skin. You can also try clothing treated with the insecticide permethrin, but don’t spray this chemical on your skin.

  • After being outdoors, check for ticks, especially in skin folds such as in the armpits, groin, and behind the ears. Remember that young ticks are tiny—about the size of a poppy seed—so they can be difficult to spot. (See these tips for removing any ticks you do find.)  

  • If you can’t do a full tick-check, pop your clothes in the dryer for 15 minutes on high, to kill any ticks that may be hiding. (See these tips for tick-proofing your yard.)

How to Tell If You've Been Infected

The most obvious way to tell if you’ve been infected with Lyme disease is to check for the telltale bull’s-eye rash (called erythema migrans), which develops in some 75 percent of cases. If you know you’ve been bitten by a blacklegged tick, you’ll want to keep a close eye out for this rash around the site of the bite.

If no such rash emerges—or if you never even found a tick on your body—but you develop symptoms of Lyme disease (fever, chills, joint pain) after being in a tick-infected area during tick season, you should ask your doctor to do a blood test.

That test has two tiers (or components) to it, and it’s important to make sure your doctor performs both. “It’s a common misconception among doctors that you can skip the first part,” says IDSA president, Paul Auwaerter, M.D. “A lot of doctors do that and they end up misinterpreting the results and misdiagnosing people.”

The timing of the tests is also important, he says. It can take weeks for the body to mount an immune response to Lyme-causing bacteria and to produce the antibodies that the blood tests are designed to measure. So if you test negative in the first month after being bitten (or after symptoms emerge), you may want to get retested a few weeks later. “The test really can’t pick up infection reliably in the first few weeks,” says Auwaerter. “But if people have had symptoms for longer than that, it’s highly accurate.”

When to Seek Treatment

If you test positive for Lyme, (or if you have a tick bite plus the telltale rash) your doctor will most likely prescribe the antibiotic doxycycline: A one- to four-week course of the drug (depending on how you respond) will almost always wipe out the infection.

But you don't necessarily have to wait for symptoms or a blood test to get treated for possible Lyme infection. In fact, many doctors say that you shouldn't wait at all. “The sooner you get treatment the better, especially for the elderly or those with weak immune systems,” says Orly Avitzur, M.D., Consumer Reports' medical director.  “Without antibiotics, the bacteria that causes Lyme can spread to your muscles, joints, heart, and brain.” 

According to the CDC and IDSA, a single dose of doxycycline taken within 72 hours of a tick bite can prevent the disease from emerging altogether.

That drug does come with side effects: It can make your skin more sensitive to sunlight, and it causes nausea or vomiting in about 20 percent of people taking it.

Some doctors may prescribe a different antibiotic, such as amoxicillin; but that approach has not been scientifically tested, and it’s unclear if or how well it works.

Another option (especially for people heading off on a sun-filled vacation) is to skip doxycycline until it’s absolutely needed. Avitzur says this watch-and-wait approach should be done in consultation with your doctor: Have a blood test to check for antibodies after a few weeks have passed, and take doxycycline if the blood test is positive or as soon as any symptoms emerge.

What Is Chronic Lyme

According to the CDC and IDSA, most people who test positive for Lyme respond well to antibiotics, even if they don’t get diagnosed or treated until months or years after the initial infection. But some patients continue to suffer, long after the standard antibiotic course.

Researchers have some ideas about the causes of this more difficult condition. It’s possible that the bacteria, or some of the toxins it produces, are sometimes able to survive the treatment. It’s also possible that the body suffers some sort of autoimmune response to the bacteria or the treatment itself. Or, it could be that these illnesses are the result of multiple simultaneous infections—not just with Borrelia burgdorferi, but with several other pathogens that the black-legged tick is known to transmit.

But ultimately, doctors are divided over several basic questions: How common is this condition? Can it be treated with antibiotics? And what should it be called?

The CDC and IDSA refer to this as post-treatment-Lyme-disease syndrome—a condition for which no proven cause or treatment options exist: According to both, there is no evidence that prolonged antibiotic therapy works against Lyme disease.

But other groups, including the International Lyme and Associated Diseases Society (ILADS) call it chronic Lyme disease. They believe that it may stem  from a failure to diagnose Lyme disease early on (often because the tell-tale rash does not emerge, and the person is not aware of being bitten by a tick). They also believe that long-term antibiotic therapy can work, though they say relapses are common and the road to recovery is bumpy.

Most doctors still reject the term chronic Lyme, in part because many people who say they have this condition have not been infected with the Borrelia bacteria. “We don’t use the term chronic Lyme because it can be confusing,” says Schwartz of the CDC. “Sometimes it is used to describe people who have tested positive for Borrelia, and who have clearly had Lyme disease. But sometimes it refers to people with no such history.”

One thing everyone agrees on is that it will take time and much more research to sort out the mystery. 

Guide to Mosquito and Tick Diseases

Where Most Cases Occur

Serious Side Effects

Symptoms appear


Common Symptoms

How to Keep Ticks out of Your Yard

Ticks love tall grass and cool, damp areas. On the "Consumer 101" TV show, Consumer Reports expert Catherine Roberts explains how to make your yard less inviting to these pests.