What causes Lyme disease?

Medically reviewed by Neka Miller, PhD on April 10, 2021. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.


Estimates from the CDC suggest that about 476,000 Americans are diagnosed with and treated for Lyme disease every year. That number can be slightly misleading since some doctors treat Lyme disease presumptively, but it still reflects how common the disease is.

Named after Lyme and Old Lyme, two towns in Connecticut, the disease presents some serious symptoms. In its most severe form, Lyme disease can be debilitating and potentially become a chronic issue. Understanding what causes Lyme disease is one of the best ways to prevent it. Read on to learn more about Lyme disease, its causes, and whether or not you should get a Lyme disease test.

What is Lyme disease?

Lyme disease is a bacterial infection that is most often associated with tick bites. Lyme disease symptoms can vary, and they often occur in stages that can overlap. Symptoms usually appear three to 30 days after the initial infected tick bite.

Following a tick bite, you will see a small, red bump at the site of the bite. The bump is similar to a mosquito bite, and it is a normal occurrence that doesn’t signal a Lyme disease infection. This bump should go away within a few days.

What causes Lyme disease?

Lyme disease is caused by four main bacterial species:

Borrelia burgdorferi Borrelia mayonii Borrelia afzelii Borrelia garinii

The latter two species are the leading causes of Lyme disease in Asia and Europe, while the former two species cause Lyme disease in the United States. These bacteria are mainly carried by black-legged ticks, also known as deer ticks. Lyme disease is most often reported in the Upper Midwestern and Northeastern states, where deer ticks are most common. However, some cases of Lyme disease have been reported in Washington, Oregon, and California.

Related: How Is Lyme Disease Transmitted?

Lyme disease is the most common tick-borne illness, though not all deer ticks necessarily have the bacteria that cause the disease. The bacteria is spread via the bite of the tick, and the infected deer tick must usually be attached for 36 to 48 hours in order to transmit the disease. This means that removing a tick as soon as possible may prevent infection. Usually, if a tick is swollen it has fed long enough to transmit the bacteria. Regardless, if you find a tick attached to you, you should get tested for Lyme disease.

Ticks can attach to any part of your body, but they will most commonly attach to folds of skin and other hard-to-see areas, including the armpits, scalp, and groin.

Early-stage symptoms of Lyme disease

Within a month of the initial infection, you will experience a rash called erythema migrans. Most (but not all) people with Lyme disease will experience this rash. It appears as a growing red area with a center that sometimes clears, creating a characteristic bull’s-eye pattern. The rash can potentially expand up to 12 inches in diameter, and while it typically isn’t painful or itchy, it can feel warm. Some people may even develop more than one of these rashes.

Along with the erythema migrans, you may experience flu-like symptoms, including:

Fever Fatigue Swollen lymph nodes Chills Headaches Body aches Neck stiffness

Later stage symptoms of Lyme disease

If you don’t receive any treatment for your infection, Lyme disease can progress to more severe symptoms. Erythema migrans may reappear on other parts of the body. You may also experience arthritis and severe joint pain. Joint pain and swelling will usually appear in the knees and other large joints, but the pain can shift to different joints. You may experience heart palpitations or an irregular heartbeat, known as Lyme carditis.

Lyme disease may also lead to neurological problems as the infection spreads to different parts of your nervous system. You may develop inflammation in the membranes surrounding the brain and spinal cord, a condition known as meningitis. The infection may cause temporary facial palsy, a paralysis in the facial muscles that can cause drooping in one or both sides of the face. Other neurological issues include:

Episodes of dizziness or shortness of breath General nerve pain Numbness or weakness in the extremities Impaired muscle movement Shooting pains in the limbs

Post-treatment Lyme disease syndrome

Most cases of Lyme disease are easily cured with a two- to four-week course of antibiotics. However, some patients may experience ongoing symptoms that last for over six months following treatment. This is known as post-treatment Lyme disease syndrome (PTLDS). Symptoms can include pain, fatigue, and difficulty thinking.

The exact mechanisms of PTLDS require further study. Some believe that the initial infection may trigger an autoimmune reaction that can continue even after the infection has been treated. Others suggest that PTLDS may come from a persistent infection that is difficult to detect. Still other experts believe that PTLDS is unrelated to Lyme disease at all.

There are currently no cures for PTLDS. Medication generally involves easing symptoms and discomfort. Most patients with PTLDS will get better on their own, but it can take several months.

Risk factors for Lyme disease

Anyone can get bitten by a tick, so everyone is at risk of Lyme disease. In the U.S., deer ticks are most common in heavily wooded, grassy areas with lots of brush and foliage. If you spend a lot of time outdoors in these types of areas, you may be at a higher risk of tick bites. This includes campers, hikers, and anyone who works in gardens, forests, and parks.

Deer ticks also tend to be more active in warmer weather, making them more plentiful in the summer. That also happens to be when people spend more time outside. You can also get bitten in the warmer months of early fall. You may even get bitten in the winter if the weather is unusually mild.

Preventing Lyme disease

The best way to prevent Lyme disease is to prevent your potential exposure to tick bites. Avoid wooded, grassy areas. If you do venture into these areas, make sure you cover up as best you can. Wear covered shoes, long pants, long-sleeved shirts, gloves, and a hat. Do your best to stick to paved or dirt trails instead of walking through tall grass, low bushes, or shrubbery.

Insect repellant can also help prevent this tick-borne illness. Applying a repellant with at least a 20 percent concentration of DEET can effectively prevent deer ticks from attaching to your skin.

If you have a yard, do your best to tick-proof it. Mow the lawn regularly, and get rid of any excess brush or leaves, which provide hiding spots for ticks. Stack your wood in dry areas that get plenty of sunlight. This discourages rodents from making nests in your wood, and rodents are frequent tick carriers.

After any time spent outside in a wooded area, make sure to check yourself, your clothing, your kids, and your pets for any ticks. Younger ticks can be tiny, no bigger than a poppy seed or the head of a pin, so be careful and diligent in your search. Taking a shower can also be a big help. Many ticks don’t immediately attach to you, but they can crawl around undetected on your skin for hours. A shower or even a thorough wipe down with a washcloth can help to knock away any ticks that haven’t yet attached.

In the event that you do find an attached tick, don’t panic, but remove it as soon as possible. All you need is a set of tweezers. Grasp the tick as close to your skin’s surface (as close to the tick’s head) as possible. Pull upward with even, steady pressure, avoiding any twisting or sudden jerking movements. This can result in the head or mouthparts breaking off and staying in the embedded skin. Should this happen, do your best to remove the mouthparts from your skin with your tweezers. If this isn’t possible, leave the parts alone and allow your skin to heal. Dispose of the tick properly (place it in alcohol, flush it down the toilet, wrap it tightly in tape), and thoroughly clean and disinfect the bite area.

Regardless of how long the tick has been attached, it’s a good idea to play it safe and get tested for Lyme disease. Everlywell offers a convenient and accurate at-home Lyme disease test that uses a simple finger prick sample collection process. If your results come back positive, our team can connect you with a care coordinator to discuss next steps for Lyme disease diagnosis and treatment.

Check out our blog for more answers to questions around Lyme disease, including “How to know if you have Lyme disease” and “Is Lyme disease contagious?”

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