Sexually transmitted infections can show up in far more places than most people expect. While the genitals are the most obvious location, STIs regularly infect the throat, rectum, eyes, skin across the body, and internal organs like the liver and brain. Many of these infections produce no symptoms at all, meaning they can exist in these locations without you ever knowing.
Genital and Urinary Tract
The genitals and urinary tract are the most common sites for STIs, simply because they’re the primary point of contact during sex. In men, infections like chlamydia and gonorrhea typically settle in the urethra, causing burning during urination or discharge. In women, the same infections tend to colonize the cervix, where they often cause no noticeable symptoms at all.
Herpes and syphilis produce visible lesions on the genitals. Herpes appears as small fluid-filled blisters that break open and ulcerate, while a primary syphilis infection creates a single firm, painless sore called a chancre. HPV causes genital warts in some cases, though most HPV infections are invisible and clear on their own.
Throat and Mouth
Oral sex transmits gonorrhea, chlamydia, herpes, syphilis, and HPV to the throat and mouth. Pharyngeal (throat) gonorrhea is the most clinically significant of these. In one study of people screened at sexual health clinics, 9.5% tested positive for throat gonorrhea. Throat chlamydia is less common, found in about 1.4% of those screened.
The tricky part is that throat infections rarely cause symptoms. Most people with pharyngeal gonorrhea or chlamydia have no sore throat or any other sign of infection, which means these infections spread unknowingly through oral sex. HPV in the throat is a growing concern because it drives rising rates of oral and throat cancers, now accounting for about 5% of all cancers worldwide.
Rectum and Anal Area
Rectal STIs are common and frequently missed. Gonorrhea, chlamydia, herpes, HPV, and syphilis all infect the rectum and surrounding skin. In a study of men who have sex with men who underwent routine screening, 53.5% of chlamydial infections were found only in the rectum, not at any other site. Among women with gonorrhea of the cervix, 35 to 50% also carry the infection in the rectum, likely from bacteria spreading from nearby genital tissue rather than from anal sex specifically.
When rectal STIs do cause symptoms, they can include anal pain, discharge (sometimes bloody), itching, and a persistent feeling of needing to have a bowel movement. Herpes in this area tends to be especially uncomfortable, producing small ulcers on the perianal skin and inside the anal canal along with pain, constipation, and sometimes fever. HPV of the anus and rectum accounts for roughly one million visits to colorectal surgeons each year, making it the most common STI seen by those specialists.
Syphilis sores in the anal area behave differently than genital ones. While genital chancres are classically painless, anal syphilis sores are frequently painful, which can lead to misdiagnosis as a simple fissure or hemorrhoid.
Eyes
Gonorrhea and chlamydia can both infect the eyes, usually through direct contact with infected genital fluids on the hands. Gonococcal eye infection causes significant pain, light sensitivity, and heavy pus-like discharge. Left untreated, it can damage the cornea rapidly. Chlamydial eye infection tends to be milder but can become chronic, causing redness, tearing, and swelling of the eyelids. In newborns, gonorrhea most commonly affects the eyes, which is why hospitals routinely apply antibiotic ointment to babies’ eyes after birth.
Skin Across the Body
Secondary syphilis is the classic example of an STI that spreads well beyond the genitals. If the initial sore goes untreated, syphilis enters the bloodstream and produces a rash that can cover the entire body. The rash is pink or dusky red and has a distinctive tendency to appear on the palms of the hands and soles of the feet, locations that most other rashes avoid. This palm-and-sole pattern is one of the key clues doctors use to identify syphilis.
Parasitic STIs also have characteristic locations on the body. Pubic lice (“crabs”) attach primarily to pubic hair but can spread to any coarse body hair, including the armpits, chest, back, beard, eyebrows, and even eyelashes. They’re diagnosed by spotting the tiny lice or their eggs (nits) attached to hair shafts in these areas.
Internal Organs and the Nervous System
Several STIs travel deep into the body when left untreated. In women, chlamydia and gonorrhea can ascend from the cervix into the uterus, fallopian tubes, and surrounding pelvic tissue, causing pelvic inflammatory disease. This inflammatory cascade can lead to scarring of the fallopian tubes, chronic pelvic pain, and fertility problems. Delays in diagnosis and treatment increase the risk of this kind of upper reproductive tract damage.
Hepatitis B and C infect the liver, where they can cause chronic inflammation, scarring (cirrhosis), and eventually liver cancer. HIV targets immune cells throughout the body via the bloodstream, gradually weakening the immune system over years if untreated. Syphilis, if it progresses through its stages without treatment, can invade the brain and nervous system (a condition called neurosyphilis), causing vision loss, hearing problems, and cognitive decline. Herpes simplex virus is a leading global cause of viral brain inflammation and infectious blindness.
Why Many Infections Go Unnoticed
One of the most important things to understand about STI location is that infections at any of these sites can be completely silent. In a study tracking patients over time, 66% of all detected STIs were asymptomatic at the time of testing. The rates varied by infection: 72.5% of chlamydia cases had no symptoms, 70% of gonorrhea cases were symptom-free, and all detected hepatitis C cases were asymptomatic.
This is especially relevant for infections outside the genitals. If you’re only tested with a urine sample or genital swab, a throat or rectal infection will be missed entirely. Current CDC screening guidelines recommend that sexually active men who have sex with men be tested at least annually at all sites of sexual contact, including the urethra, rectum, and throat. For women, rectal and throat testing is recommended based on sexual history and a conversation with a provider. These site-specific tests use simple swabs and are the only way to catch infections hiding in locations that produce no symptoms.