Gonorrhea is caused by a bacterium called Neisseria gonorrhoeae, which spreads almost exclusively through sexual contact. It passes from person to person during vaginal, anal, or oral sex without a condom when one partner carries the infection. A pregnant person with gonorrhea can also pass it to their baby during delivery. Beyond these routes, transmission is extremely rare because the bacterium is fragile and dies quickly outside the human body.
The Bacterium Behind Gonorrhea
Neisseria gonorrhoeae is a tiny, kidney bean-shaped bacterium that typically appears in pairs under a microscope. It cannot form protective spores, cannot move on its own, and requires oxygen to survive. These characteristics make it poorly suited to life outside a human host, which is why gonorrhea doesn’t spread through toilet seats, swimming pools, or casual contact like handshakes or hugging.
What the bacterium lacks in environmental toughness, it makes up for in its ability to exploit the warm, moist surfaces of the human body. It targets the mucous membranes lining the reproductive tract, rectum, throat, and eyes. These tissues provide exactly the conditions the bacterium needs: warmth, moisture, and a rich supply of cells it can latch onto and invade.
How the Infection Spreads
Gonorrhea spreads through direct contact with infected mucous membranes or the fluids they produce. The three main routes are vaginal sex, anal sex, and oral sex. During any of these, the bacterium transfers from the infected tissue of one person to the susceptible tissue of another. Ejaculation does not need to occur for transmission to happen.
The infection can also pass from a mother to her newborn during vaginal delivery. As the baby moves through the birth canal, the bacterium can infect the baby’s eyes, potentially causing a serious condition that can lead to blindness if untreated. This is one reason newborns routinely receive antibiotic eye drops shortly after birth.
People who have sex without condoms, have multiple partners, or have had gonorrhea before face a higher likelihood of infection. Notably, a previous infection provides no lasting immunity. You can catch gonorrhea repeatedly throughout your life.
What Happens Inside the Body
Once the bacterium reaches a mucous membrane, it uses hair-like filaments on its surface called pili to make initial contact with human cells. Think of these as tiny grappling hooks that anchor the bacterium in place before it can be swept away by natural body fluids. After this first grip, the bacterium deploys a second set of surface proteins that lock it tightly to specific receptors on human cells, triggering the cell to essentially pull the bacterium inside.
In the cervix, for example, the bacterium preferentially colonizes the outer portion, where the lining cells are flat and layered. It uses signals from its surface proteins to reorganize the cell’s internal scaffolding, causing the cell membrane to reach out and engulf the bacterium. Once inside, the bacterium can cross through the cell layer and reach deeper tissue, where it triggers the intense inflammation that produces gonorrhea’s characteristic symptoms.
The bacterium can infect several sites depending on the type of sexual contact. Vaginal sex can lead to infection of the cervix, uterus, and fallopian tubes. Anal sex can infect the rectum. Oral sex can infect the throat. In all cases, the process is the same: the bacterium attaches, invades, and provokes an immune response that causes swelling, pain, and discharge.
Why Your Immune System Struggles to Stop It
One of the most important reasons gonorrhea remains so common is the bacterium’s remarkable ability to disguise itself from the immune system. It does this through a process called antigenic variation, constantly reshuffling the genetic code for its surface proteins so that the version your immune system learns to recognize is quickly replaced by a new one.
Specifically, the bacterium keeps a library of silent, unused gene segments for its pili. Through a form of internal genetic recombination, it swaps portions of its active pili gene with segments from this silent library, producing pili with a different molecular appearance. By the time your immune cells have built antibodies against one version, the bacterium is already wearing a different disguise. This is also why having gonorrhea once doesn’t protect you from getting it again. Your immune system essentially has to start from scratch each time.
The bacterium’s outer membrane also carries proteins that interfere with the immune cells trying to engulf and destroy it. These proteins block the normal process by which white blood cells consume bacteria, giving the infection more time to establish itself and spread to new cells.
How Quickly Symptoms Appear
Symptoms typically begin 1 to 14 days after exposure, though many people never develop noticeable symptoms at all. This silent period is a major driver of transmission because people who feel fine continue having sex without knowing they’re infected.
When symptoms do appear, they differ by site. A genital infection commonly causes painful urination and unusual discharge. A rectal infection may cause itching, soreness, or discharge. A throat infection often produces no symptoms or may feel like a mild sore throat that’s easy to dismiss. The wide variation in symptoms, combined with the possibility of no symptoms at all, means many infections go undetected without testing.
Scale of the Problem
Gonorrhea remains one of the most commonly reported bacterial infections worldwide. In the United States, it is part of the more than 2.2 million combined cases of chlamydia, gonorrhea, and syphilis reported in 2024. There is some encouraging news: gonorrhea cases have declined for three consecutive years, dropping 10% from 2023 to 2024. Still, the numbers remain substantial, and antibiotic resistance in gonorrhea is a growing concern that makes each infection harder to treat than it would have been a decade ago.
The combination of easy transmission, frequent lack of symptoms, and the bacterium’s talent for evading immunity makes gonorrhea a persistent public health challenge. Consistent condom use and regular STI testing, particularly for people with new or multiple partners, remain the most effective ways to prevent infection and catch it early when it does occur.