What Is Lyme Disease? Symptoms, Causes, Diagnosis, and Treatment

What is Lyme disease?

Lyme disease is an infection caused by bacteria. In the United States, the usual cause is a germ called Borrelia burgdorferi. A related germ, Borrelia mayonii, causes it rarely. ^[1]

The bacteria live in ticks. When an infected tick bites you and stays attached long enough, the bacteria can pass into your skin and then spread through your body. From there they can affect the skin, joints, nerves, and heart.

Lyme disease is named after Lyme, Connecticut, where a cluster of cases was identified in the 1970s. It is now the most common tick-borne illness in the United States.

The CDC estimates that around 476,000 people are diagnosed and treated for Lyme disease each year. This is much higher than the number of cases officially reported. ^[7]

How do you get Lyme disease?

You get Lyme disease from the bite of an infected blacklegged tick. In the Northeast, mid-Atlantic, and upper Midwest, this is commonly called the deer tick. On the Pacific Coast, the western blacklegged tick can spread the infection. ^[1]

Not every tick carries the bacteria, and not every bite from an infected tick leads to Lyme disease.

In most cases, the tick must remain attached for about 36 to 48 hours or longer before the bacteria can pass to you. ^[9] That is why checking for ticks and removing them quickly matters.

Young ticks, called nymphs, are about the size of a poppy seed. They cause many infections because they are easy to miss. You may never notice the tick that bit you.

Where and when is Lyme disease most common?

Lyme disease is most common in the Northeast, mid-Atlantic, and upper Midwest of the United States. ^[1] It also occurs along the Pacific Coast and in parts of Canada and Europe.

Most infections happen during late spring and summer, with a peak in June and July. However, ticks may remain active during mild weather in other seasons.

Wooded areas, tall grass, brush, and leaf litter are common environments where people encounter ticks.

What are the symptoms of Lyme disease?

Symptoms depend on how long the infection has been in the body. ^[2]

Many Lyme disease symptoms resemble other illnesses, including the flu. That is one reason the infection can be missed, especially when there is no obvious rash or known tick bite.

For more information about how Lyme disease can affect the joints and contribute to lasting symptoms, read our guide to chronic inflammation and Lyme disease .

You can also explore our Lyme disease symptoms hub.

Does everyone get the bull’s-eye rash?

No. The typical Lyme disease rash, called erythema migrans, appears in roughly 70 to 80 percent of infected people. It usually expands gradually over several days. ^[2]

The classic bull’s-eye appearance is only one possible pattern. Many Lyme rashes appear as a solid red patch rather than a ring. On darker skin, the rash may appear bruised or blue-red.

A rash that continues expanding after possible tick exposure deserves medical attention, even if it does not resemble a bull’s-eye.

How is Lyme disease diagnosed?

Doctors diagnose Lyme disease using your symptoms, a physical examination, and the possibility of exposure to infected ticks.

When someone has a typical expanding Lyme rash in an area where the disease is common, treatment can begin without waiting for blood tests. ^[6]

When blood tests are used, they usually look for antibodies made by the immune system in response to the bacteria. Standard testing is performed in two steps. ^[3]

Two important limitations are worth understanding:

• Early tests can be negative. Antibodies may take several weeks to develop.
• Tests may remain positive after treatment. Antibodies can stay in the bloodstream for months or years, so a positive test does not necessarily indicate an active infection.

Testing people without symptoms typical of Lyme disease is generally not recommended. Testing a removed tick is also not normally used to decide whether treatment is needed.

How is Lyme disease treated?

Lyme disease is treated with antibiotics. Common choices include doxycycline, amoxicillin, and cefuroxime axetil.

The medication and length of treatment depend on your symptoms, age, allergies, pregnancy status, and which parts of the body are affected. Most cases are treated with antibiotic courses lasting from 10 days to about four weeks. ^[4]

People treated early usually recover quickly and completely. ^[1] Infections affecting the nervous system, heart, or joints may require different treatment approaches.

Antibiotics are not recommended automatically after every tick bite. In certain high-risk situations, a single dose of doxycycline soon after a bite may reduce the chance of developing Lyme disease. ^[6]

Contact a healthcare professional promptly after a possible high-risk tick bite to discuss whether preventive treatment is appropriate.

What if symptoms continue after treatment?

Some people continue experiencing fatigue, body aches, or difficulty thinking after completing recommended antibiotic treatment.

When the symptoms meet certain criteria, this is called post-treatment Lyme disease syndrome, or PTLDS. Researchers are still investigating why these symptoms continue in some people. ^[5]

You may also encounter the term “chronic Lyme disease.” This phrase is used in different ways and does not have one universally accepted medical definition.

Persistent symptoms deserve medical attention even when their cause remains unclear.

Our guide to chronic inflammation and Lyme disease explains what researchers know about inflammation and symptoms that continue after treatment.

What happens if Lyme disease is not treated?

Without treatment, Lyme disease can spread beyond the initial bite area and affect the joints, heart, and nervous system.

Possible complications include arthritis, facial weakness, nerve pain, and heart rhythm abnormalities. ^[2]

These complications can often be treated, but identifying and treating Lyme disease early generally makes recovery easier.

Is Lyme disease contagious?

No. Lyme disease does not spread between people through touching, coughing, sharing food, or ordinary contact.

In the United States, Lyme disease is primarily spread through bites from infected blacklegged ticks. The CDC has found no evidence that it spreads through sexual contact or breast milk. ^[9]

Dogs and other pets can also develop Lyme disease after infected tick bites. Pets do not transmit the infection directly to people, but they may carry ticks indoors.

Can you get Lyme disease more than once?

Yes. Having Lyme disease once does not provide lasting immunity against another infection.

A person can become infected again after another bite from an infected tick.

New symptoms or an expanding rash following another possible tick exposure should be evaluated, even if you have previously received treatment for Lyme disease.

How can you prevent Lyme disease?

Preventing tick bites is the most effective way to reduce the risk of Lyme disease. ^[1]

Important prevention steps include:

• Use EPA-registered insect repellents according to their instructions.
• Wear long sleeves and pants when walking through wooded or grassy areas.
• Stay on cleared trails and avoid brushing against tall vegetation.
• Check your body for ticks after spending time outdoors, including behind the knees, underarms, scalp, and groin.
• Check children and pets for ticks.
• Shower after outdoor activities and dry clothing using high heat when appropriate.
• Remove attached ticks promptly using fine-tipped tweezers.

Visit our Lyme disease prevention hub for more information about tick checks, removal, and what to do after a bite.

Is there a Lyme disease vaccine?

As of October 2026, no Lyme disease vaccine is approved for human use in the United States.

An earlier Lyme disease vaccine was withdrawn from the market in 2002. ^[8]

Pfizer and Valneva have developed a new candidate vaccine. In a large phase 3 trial, it reduced confirmed Lyme disease cases by approximately 73 percent.

However, fewer participants developed Lyme disease than expected, and the trial did not meet its primary statistical objective.

The companies are pursuing regulatory approval, and decisions remain pending. ^[8]

Until an effective vaccine becomes available, preventing tick bites remains the primary way to reduce the risk of Lyme disease.

When should I see a doctor?

Contact a healthcare professional if you develop symptoms after possible exposure to infected ticks.

Important warning signs include:

• An expanding rash, fever, headache, or body aches after possible tick exposure.
• A tick that may have remained attached for a day or longer.
• New joint swelling or weakness on one side of the face.
• Numbness, tingling, or severe headache with neck stiffness.
• Heart palpitations, dizziness, or fainting.

Tell your healthcare provider where you were, when the possible bite occurred, and how long the tick may have been attached.

The takeaway

Lyme disease is a bacterial infection spread through infected tick bites. It is common in several regions of the United States and can affect the skin, joints, nervous system, and heart.

Most people recover fully when the infection is identified and treated early with antibiotics.

Preventing tick bites, checking for ticks, and seeking medical attention when symptoms develop are important ways to protect your health.

If symptoms continue after treatment, a medical evaluation can help identify possible causes and determine appropriate next steps.