Lyme disease is an infection spread by tick bites, caused by a bacterium that enters your bloodstream and can affect your joints, heart, and nervous system

Lyme disease starts when an infected tick bites you and a spiral-shaped bacterium called Borrelia burgdorferi enters your skin. The tick must stay attached for roughly 24 to 48 hours to transmit the infection—a quick brush against your clothing usually does not transfer it. Once the bacterium enters your body, it spreads through your bloodstream and can settle in your joints, heart, nervous system, and other tissues. The infection is treatable with antibiotics in its early stages, but if left untreated, it can cause lasting problems.

Lyme disease is not contagious from person to person. You cannot catch it from someone who has it, and you cannot spread it to others. The only way to get infected is through a tick bite from a tick that carries the bacterium.

Key Takeaways

  • Lyme disease is caused by a bacterium transmitted through infected tick bites and can affect multiple body systems including joints, nerves, and the heart.
  • The characteristic rash called erythema migrans appears in about 70 to 80 percent of infected people, usually within 3 to 30 days of the tick bite.
  • Early-stage Lyme disease is treated with oral antibiotics like doxycycline or amoxicillin, which are most effective when started within the first few weeks of infection.
  • Without treatment, the infection can progress to late-stage Lyme disease, causing arthritis, neurological problems, and heart rhythm disturbances that may require longer treatment courses.
  • Ticks that carry Lyme disease are found across North America, Europe, and Asia, with highest concentrations in the northeastern and upper midwestern United States.

How the infection spreads through your body

When an infected tick bites you, the bacterium does not immediately flood your bloodstream. Instead, it multiplies at the bite site and gradually spreads outward in a circular pattern. This spreading infection is what creates the characteristic rash called erythema migrans—a red, expanding circle that often looks like a target or bullseye. The rash appears in roughly 70 to 80 percent of people infected with Lyme disease, typically within 3 to 30 days of the bite.

As the bacterium spreads, it can reach your joints, where it triggers inflammation and pain. It can also cross into your nervous system, affecting nerves and the brain, or reach your heart and disrupt its electrical signals. The longer the infection goes untreated, the more likely it is to settle into these tissues and cause problems that persist even after antibiotics kill the bacteria.

Early-stage symptoms and when they appear

Early Lyme disease often feels like the flu. You may experience fatigue, muscle aches, headache, fever, and chills within the first few weeks after infection. Some people have no symptoms at all during this stage, which is why the rash—if it appears—becomes the most reliable early warning sign. The rash does not itch or hurt; it simply expands outward from the bite site.

Not everyone develops a rash, and not everyone feels sick. Some people have only joint pain or only neurological symptoms. This variation makes early Lyme disease easy to miss, especially if you do not remember being bitten by a tick. Ticks are small—some are the size of a poppy seed—and their bites are usually painless.

Late-stage Lyme disease and untreated infection

If early Lyme disease is not treated, the infection can progress to late-stage disease weeks or months later. At this point, the bacterium has established itself in your joints, nervous system, or heart, and the problems it causes become harder to reverse.

Lyme arthritis is the most common late-stage complication. It typically affects large joints like the knees, causing swelling, pain, and stiffness that can last for months or years. Lyme neuroborreliosis affects the nervous system and can cause facial paralysis (Bell's palsy), shooting nerve pain, memory problems, or difficulty concentrating. Lyme carditis disrupts the heart's electrical system and can cause irregular heartbeats or fainting. Late-stage disease requires longer courses of antibiotics, sometimes given intravenously, and some damage may not fully resolve.

Geographic distribution and tick species

Lyme disease is found across the Northern Hemisphere. In North America, it is most common in the northeastern United States (from Maine to Virginia) and the upper Midwest (particularly Wisconsin and Minnesota), though cases have been reported in most states. In Europe, it occurs across much of the continent, and in Asia, it is found in parts of Russia, China, and Japan.

The infection is carried by hard ticks in the genus Ixodes. In North America, the primary vector is the blacklegged tick (also called the deer tick). These ticks are active in spring, summer, and fall, with peak activity in May and June. They live in wooded areas, tall grass, and leaf litter, and they attach to humans and animals that brush past vegetation.

How diagnosis works

Diagnosis of Lyme disease relies on a combination of symptoms, exposure history, and blood tests. If you have the characteristic rash and remember a tick bite or time spent in a tick-prone area, your doctor may start treatment based on clinical signs alone, without waiting for test results. This is important because early treatment is most effective.

Blood tests detect antibodies your immune system produces in response to the infection. However, these antibodies take time to develop—they may not show up in the first week or two of infection. A negative test early in the disease does not rule out Lyme disease. The standard approach is a two-step test: an initial screening test (ELISA), followed by a more specific confirmatory test (Western blot) if the first is positive. Testing is most reliable after the first few weeks of infection.

Treatment and antibiotic options

Early-stage Lyme disease is treated with oral antibiotics. Doxycycline is the first choice for adults and children over 8 years old, taken for 14 to 21 days. Amoxicillin or cefuroxime are alternatives for pregnant women and young children, who cannot take doxycycline. These antibiotics are effective at stopping the spread of the bacterium and preventing progression to late-stage disease.

Late-stage Lyme disease, particularly neurological or cardiac involvement, may require intravenous antibiotics like ceftriaxone, given in a hospital or outpatient clinic over 14 to 28 days. The longer treatment course reflects the fact that the bacterium has become established in tissues that are harder for antibiotics to reach. Even with appropriate treatment, some symptoms—particularly joint pain—may take months to fully resolve.

Post-treatment Lyme disease syndrome

Some people continue to experience fatigue, joint pain, or cognitive difficulties for months after completing antibiotic treatment. This condition is called post-treatment Lyme disease syndrome (PTLDS) or sometimes "chronic Lyme disease," though the latter term is not standard medical terminology. The cause is not fully understood—it may reflect lingering inflammation, incomplete bacterial clearance in certain tissues, or damage that occurred before treatment began.

PTLDS is not the same as active infection. Blood tests do not show ongoing bacterial activity, and additional antibiotics do not reliably improve symptoms. Treatment focuses on managing individual symptoms—pain management, physical therapy for joint problems, cognitive rehabilitation for memory or concentration issues. Research into PTLDS is ongoing, and the condition remains an area of active investigation.

Frequently Asked Questions

Can you get Lyme disease more than once?

Yes. Infection with Lyme disease does not create lasting immunity, so you can be infected again if bitten by another infected tick. This is why tick prevention remains important even if you have had Lyme disease before.

What should I do if I find a tick on my skin?

Remove it with fine-tipped tweezers by grasping it as close to the skin as possible and pulling straight out. Do not twist, crush, or squeeze the tick, as this can push bacteria into your skin. Clean the bite area with soap and water or rubbing alcohol. Save the tick in a sealed bag if possible—some areas offer tick testing to determine if it carried Lyme disease.

Is there a vaccine for Lyme disease?

A vaccine called LYMErix was available in the United States from 1998 to 2002 but was withdrawn from the market due to low demand following safety concerns that were later found to be unfounded. No Lyme disease vaccine is currently available in the United States, though vaccines exist in some European countries.

How can I reduce my risk of tick bites?

Wear long sleeves and pants when in wooded or grassy areas, tuck pants into socks, and use insect repellent containing DEET or permethrin on skin and clothing. Check your entire body for ticks after being outdoors, paying special attention to warm, moist areas like armpits and the groin. Shower within a few hours of coming indoors, as this can wash off unattached ticks.

Does everyone bitten by an infected tick develop Lyme disease?

No. Studies suggest that roughly 1 to 3 percent of tick bites in endemic areas result in Lyme disease. Factors that influence whether infection develops include how long the tick was attached, the bacterial load in the tick, and possibly individual immune response, though the exact reasons some people develop infection and others do not are not fully understood.