You catch Lyme disease from the bite of an infected black-legged tick, commonly called a deer tick. There is no other known way to get it. The bacterium that causes the infection lives inside the tick’s gut and only reaches you after the tick has been attached and feeding for a prolonged period, typically more than 24 hours.
What Happens During a Tick Bite
The bacteria responsible for Lyme disease, called Borrelia burgdorferi, live in a dormant state inside a tick’s midgut between feedings. When the tick latches onto your skin and begins drawing blood, the influx of warm mammalian blood triggers the bacteria to “wake up.” They start multiplying, push through the wall of the tick’s gut, and migrate into the tick’s salivary glands. From there, the bacteria flow into your skin through the tick’s saliva as it feeds.
This biological process takes time, which is why the duration of attachment matters so much. In most cases, a tick must be feeding for more than 24 hours before enough bacteria reach the salivary glands to cause infection. CDC guidance for clinicians sets the higher-risk threshold at 36 hours or more of attachment. That window gives you a real opportunity: if you find and remove a tick within 24 hours, you can greatly reduce your chances of getting Lyme disease.
Which Ticks Carry Lyme Disease
Only black-legged ticks transmit Lyme disease. In the eastern United States, the species is Ixodes scapularis, found throughout the Northeast, Mid-Atlantic, and upper Midwest. On the West Coast, the western black-legged tick (Ixodes pacificus) is the carrier. Other common ticks, like the American dog tick or the lone star tick, do not transmit Lyme disease.
Black-legged ticks are smaller than you might expect. Adults are roughly 3 millimeters long, about the size of a sesame seed. Nymphs, the immature stage, are under 2 millimeters, closer to a poppy seed. They have a dark brown to black shield on their backs with no white markings, and noticeably long mouthparts compared to other tick species. Those long mouthparts help them anchor firmly into the skin, which is part of why their bites often go unnoticed.
Why Nymphs Are the Biggest Threat
Nymphal ticks are responsible for a large share of Lyme infections. Their tiny size makes them extremely difficult to spot on your body, so they’re more likely to feed undetected long enough to transmit bacteria. Nymphs are most active in late spring and summer, roughly May through July, which lines up with the peak season for Lyme disease cases. Adult ticks are easier to find because of their larger size, and they’re most active in the cooler months of fall and early spring.
Where Lyme Disease Is Most Common
Lyme disease is heavily concentrated in specific parts of the United States. Over 89,000 cases were reported to the CDC in 2023 alone. The highest-incidence states cluster in the Northeast (Maine, Massachusetts, Connecticut, New York, New Jersey, Pennsylvania), the upper Midwest (Wisconsin, Minnesota), and parts of the Mid-Atlantic region. Cases do occur on the West Coast and in other states, but at much lower rates.
If you live in or travel to these high-incidence areas and spend time outdoors in wooded or grassy environments, your risk of encountering an infected tick is significantly higher. Ticks thrive in leaf litter, tall grass, and the brushy edges where lawns meet forests.
You Can’t Catch It From Other People or Insects
Lyme disease does not spread from person to person. You cannot catch it through touching, kissing, or sexual contact with someone who has Lyme disease. It does not spread through mosquito bites, flea bites, or any other insect. The only established route of transmission is the bite of an infected Ixodes tick.
The question of whether a pregnant person can pass the infection to their fetus is more nuanced. A systematic review of the available evidence found that vertical transmission is biologically plausible but appears to be rare, with very limited documented cases. However, untreated Lyme disease during pregnancy was associated with adverse birth outcomes in roughly 50% of cases in pooled data, compared to about 11% when the infection was treated. Prompt treatment during pregnancy significantly lowers that risk.
What to Do After a Tick Bite
If you find a tick attached to your skin, remove it as soon as possible using fine-tipped tweezers. Grasp the tick as close to the skin surface as you can and pull upward with steady, even pressure. Don’t twist or jerk, which can cause the mouthparts to break off in your skin. After removal, clean the bite area with rubbing alcohol or soap and water.
A single preventive dose of doxycycline may be appropriate when specific conditions are met: the bite happened in a high-incidence area, the tick is identified as a black-legged tick (adult or nymph), the estimated attachment time was 36 hours or more, and the medication can be started within 72 hours of removing the tick. If you’re unsure whether these criteria apply to you, bring the tick to your healthcare provider or take a clear photo of it.
The First Sign of Infection
The most recognizable early sign of Lyme disease is a spreading rash called erythema migrans, which appears in over 70% of infected people. It typically develops 3 to 30 days after the bite and gradually expands over several days. The rash can reach 12 inches or more across and sometimes develops a “bull’s-eye” pattern with a clear center, though many Lyme rashes are uniformly red without that classic ring shape. It usually feels warm to the touch but is rarely itchy or painful.
Not everyone develops a rash, and not everyone notices it. When the rash appears on the scalp, behind a knee, or on the back, it can easily be missed. Early symptoms that accompany or replace the rash include fever, fatigue, headache, and muscle or joint aches. These can feel like a summer flu. If you develop any of these symptoms within a few weeks of spending time in tick habitat, especially if you found a tick on your body, it’s worth getting evaluated promptly. Early treatment is highly effective at clearing the infection before it progresses.