Lyme disease is a bacterial infection spread through the bites of infected ticks. It is the most common tick-borne illness in the United States, with an estimated 476,000 people diagnosed and treated for it each year. When caught early, most cases resolve with a short course of antibiotics, but untreated Lyme disease can spread to the joints, heart, and nervous system over weeks to months.
How Lyme Disease Spreads
Lyme disease is caused by a type of spiral-shaped bacteria. In the United States, two closely related species are responsible. The vast majority of cases come from one species, while a second, rarer species was identified more recently in the upper Midwest.
The bacteria travel to humans through infected blacklegged ticks (sometimes called deer ticks). In the eastern United States, one species of blacklegged tick is the primary carrier. In the far western states, a close relative, the western blacklegged tick, fills that role. Not every tick carries the bacteria, and not every bite from an infected tick leads to illness. The tick generally needs to be attached for a prolonged period before the bacteria transfer, which is why finding and removing ticks quickly is one of the best defenses.
Lyme disease is most common in the Northeast, mid-Atlantic, and upper Midwest, though its geographic range has expanded significantly since the mid-1990s. Over 89,000 cases were reported to the CDC in 2023 alone, and the true number is likely much higher because many cases go unreported.
The Earliest Sign: The Rash
The hallmark of early Lyme disease is a skin rash that appears at the site of the tick bite, typically between 3 and 30 days after the bite (about 7 days on average). This rash shows up in roughly 70 to 80 percent of infected people, which means a significant minority never develop one at all.
Most people picture a “bull’s-eye” pattern: a red ring with a clear center. In reality, that classic look is uncommon. One study of early Lyme rashes found only about 6 percent had the textbook bull’s-eye or ring-within-a-ring pattern. The majority (51 percent) were uniform in color without central clearing, and most were pink, oval-shaped, and had well-defined borders. Some rashes appear with a darker or more intensely red center, and in rare cases they can blister. The rash expands gradually over several days and can grow to 12 inches or more across. It may feel warm to the touch but is rarely itchy or painful.
Because the rash looks different from what many people expect, it’s easy to dismiss or mistake for a spider bite or skin irritation. Recognizing any expanding red rash after time spent in tick-prone areas is important, even if it doesn’t look like a target.
Symptoms Beyond the Rash
Lyme disease progresses through stages if left untreated. Early on, even without a visible rash, you may experience fever, chills, headache, fatigue, muscle and joint aches, and swollen lymph nodes. These symptoms overlap with many common illnesses, which is part of what makes Lyme tricky to identify without the rash.
Over the following days to months, the bacteria can spread throughout the body. At this point, symptoms become more serious and varied:
- Nervous system: Severe headaches, neck stiffness, facial palsy (a droop on one or both sides of the face), nerve pain, and shooting pains or tingling in the hands and feet. In some cases, the brain and spinal cord become inflamed.
- Joints: Arthritis with severe pain and swelling, particularly in the knees and other large joints. Pain may come and go, affecting tendons, muscles, and bones.
- Heart: A condition called Lyme carditis can develop, causing heart palpitations, an irregular heartbeat, dizziness, or shortness of breath.
Additional rashes can also appear on other parts of the body during this stage, separate from the original bite site. The later symptoms become harder to treat the longer the infection goes unaddressed.
How Lyme Disease Is Diagnosed
Diagnosis relies on a combination of symptoms, exposure history, and blood tests. If you have a classic expanding rash and recent tick exposure, your doctor may diagnose Lyme disease based on those signs alone, without waiting for lab results.
When blood tests are needed, the standard approach uses a two-step process. The first test screens for antibodies your immune system produces in response to the bacteria. If that test is positive or borderline, a second, more specific test confirms the result. This two-tier system helps reduce false positives.
Timing matters. If you’re tested within the first two weeks of infection, the results may come back negative because your body hasn’t produced enough antibodies yet. If recent infection is suspected despite a negative result, retesting with a new blood sample in 7 to 14 days is typically recommended. For people who have had symptoms for more than 30 days, only the longer-term antibody test is considered reliable, since the short-term antibody test can produce misleading results at that point.
Treatment and Recovery
Most cases of Lyme disease are treated with 10 to 14 days of oral antibiotics. The medications most commonly used are doxycycline, amoxicillin, or cefuroxime axetil. When treated early, the vast majority of people recover fully.
In some situations, a single dose of doxycycline given shortly after a tick bite in a high-risk area can lower the chance of developing Lyme disease in the first place. This preventive approach isn’t appropriate for every tick bite but may be offered when the risk is high enough.
More advanced cases involving the heart or nervous system may require longer or more intensive antibiotic treatment, but the principle is the same: the earlier treatment begins, the better the outcome.
Lingering Symptoms After Treatment
Some people continue to experience symptoms after completing antibiotic treatment. This is known as Post-Treatment Lyme Disease Syndrome. The most common lingering problems are fatigue, body aches, and difficulty with thinking and memory. The cause is not fully understood, and the experience varies from person to person.
For some, the dominant symptom is persistent exhaustion. For others, it’s cognitive fog, sometimes described as trouble concentrating or finding words. These symptoms can last for weeks to months and, in a smaller number of cases, longer. There is currently no proven treatment that speeds recovery from this syndrome, and additional rounds of antibiotics have not been shown to help.
Preventing Tick Bites
Prevention starts with reducing your exposure to ticks. When spending time in wooded or grassy areas, wearing long pants and sleeves and using insect repellent on exposed skin and clothing makes a real difference. After coming indoors, checking your entire body for ticks is one of the most effective steps you can take, since prompt removal can prevent transmission.
If you find an attached tick, use fine-tipped tweezers to grasp it as close to your skin as possible. Pull upward slowly and evenly without twisting or jerking, which can cause the mouthparts to break off in the skin. After removal, clean the bite area with soap and water or rubbing alcohol, and wash your hands. Save the tick in a sealed bag if you want to have it identified later.
Showering within two hours of coming indoors and tossing clothes in the dryer on high heat for 10 minutes can kill any ticks you might have missed. Pets can also carry ticks indoors, so checking them after outdoor time helps protect the whole household.