What is Lyme disease? A plain-language guide

Quick answer

Lyme disease is a bacterial infection spread to people by the bite of an infected blacklegged (deer) tick. In the United States it is caused by Borrelia burgdorferi and, rarely, Borrelia mayonii. Early signs include fever, fatigue and an expanding rash. Most people recover fully with a few weeks of antibiotics.

Lyme disease facts at a glance

Want to separate fact from fiction? Read Lyme disease myths, or learn how the disease was discovered in the history of Lyme disease.

What causes Lyme disease?

Lyme disease is caused by spiral-shaped bacteria. In the United States, CDC names two species: Borrelia burgdorferi, which causes almost all cases, and Borrelia mayonii, which is rare. These germs live in small wild animals, mostly rodents. Young ticks pick up the bacteria when they feed on an infected animal, then can pass it to a person at their next meal.

Deer matter because adult ticks feed on them, which helps tick numbers grow. But deer themselves are not infected and do not infect ticks, according to CDC. For a deeper look, read what causes Lyme disease.

How do people get Lyme disease?

Almost always from a tick bite. Two ticks spread Lyme disease in the U.S.:

• Blacklegged tick (deer tick) in the Northeast, mid-Atlantic and north-central states.
• Western blacklegged tick along the Pacific coast.

The highest-risk stage is the nymph, a young tick about the size of a poppy seed that is easy to miss. Nymphs are most active from April through July. CDC says an infected tick generally has to stay attached for more than 24 hours to pass on the infection, so finding and removing ticks quickly really helps. See our guides to ticks that carry Lyme disease and how long a tick needs to be attached.

Lyme disease is not spread by touching, kissing or sex, and there is no credible evidence that mosquitoes, fleas, food, air or water spread it (CDC). More on that in how Lyme disease is transmitted and is Lyme disease contagious?

What does Lyme disease do to the body?

The infection starts in the skin around the bite. If it is not treated, the bacteria can travel through the body to the joints, heart and nervous system. Doctors often describe it in stages (see stages of Lyme disease):

• Early (about 3 to 30 days after the bite): fever, chills, headache, tiredness, muscle and joint aches, swollen lymph nodes, and often a rash called erythema migrans. CDC says the rash shows up in about 70 to 80 percent of infected people. It grows over several days, may feel warm, and is rarely itchy or painful. Only some rashes look like a bull’s-eye. See Lyme disease rash.
• Later (days to months after the bite): more rashes on other parts of the body, severe headaches and neck stiffness, facial drooping (facial palsy), nerve pain, numbness or tingling, an irregular heartbeat, and arthritis with painful, swollen joints, especially the knees.

Read the full Lyme disease symptoms guide, or the focused guides on neurological Lyme disease, Lyme arthritis and Lyme carditis.

Where is it found, and how common is it?

Lyme disease is most common in the Northeast, mid-Atlantic and upper Midwest. CDC estimates that about 476,000 people may be diagnosed and treated for it each year, based on insurance data, and notes this may be an overestimate. States reported 89,468 cases in 2023. Explore the risk map, Lyme disease by state, or how common Lyme disease is.

How is Lyme disease diagnosed?

There is no single quick test. A provider looks at your symptoms, checks for the rash, and asks whether you could have been near infected ticks. CDC recommends FDA-cleared antibody blood tests when testing is needed. Antibodies can take a few weeks to show up, so early tests may be negative. Learn more in our Lyme disease test guide.

Treatment and recovery

Lyme disease is treated with antibiotics. CDC says the drugs most often used are doxycycline, amoxicillin or cefuroxime axetil, usually for 10 days to 4 weeks. Your provider chooses the medicine and length based on your symptoms, age, allergies and whether you are pregnant. People treated early usually recover quickly and completely. See Lyme disease treatment and is Lyme disease curable?

When symptoms linger

Some people still have tiredness, body aches or trouble thinking after treatment. CDC calls this post-treatment Lyme disease syndrome (PTLDS). The cause is unknown. Most people improve over time, though it can take many months. CDC says studies found long-term antibiotics were no better than placebo for these symptoms and can cause serious harm.

Many patients and advocacy groups use the term “chronic Lyme disease” and believe ongoing infection plays a role. CDC discourages that term because ongoing infection has not been shown to cause these symptoms. We explain both views in chronic Lyme disease.

How to prevent Lyme disease

The best protection is avoiding tick bites. That also lowers your risk of other diseases ticks carry. Use repellent, check your body and your pets after time outdoors, and remove attached ticks as soon as you can. Our prevention guide and tick bite guide walk you through it. For the latest on vaccines, see our Lyme disease vaccine page, and for pets, the Lyme vaccine for dogs.

More answers about Lyme disease

Have a specific question? Our Lyme disease questions hub answers the most common ones, including can Lyme disease kill you, how long it lasts, whether you can get it twice and whether it is permanent. Or browse all guides.

Frequently asked questions