Many sexually transmitted infections produce no symptoms at all, which is why they spread so easily. When signs do appear, the most common ones include unusual discharge from the penis or vagina, sores or blisters on or around the genitals, painful urination, and itching or redness in the genital area. But symptoms vary widely depending on the specific infection, and some look nothing like what you’d expect.
Why Many STIs Cause No Symptoms
It’s possible to carry and transmit an STI without ever feeling sick or noticing anything unusual. Women are especially likely to have silent infections. Chlamydia and gonorrhea, two of the most common STIs, frequently produce no symptoms in women. When they do cause discharge or burning, women often mistake the signs for a yeast infection. Men tend to notice symptoms like unusual penile discharge more readily because it’s clearly out of the ordinary for them.
Anatomy plays a role in this difference. The vaginal lining is thinner and more delicate than the skin on a penis, making it easier for bacteria and viruses to take hold. Genital sores from herpes or syphilis can also develop inside the vagina where they aren’t easily visible, while men are more likely to spot sores on the penis.
Discharge, Burning, and Pelvic Pain
Chlamydia, gonorrhea, and trichomoniasis are the STIs most likely to cause discharge and urinary symptoms. They share overlapping signs, which makes it hard to tell them apart without testing.
Chlamydia typically shows up one to three weeks after exposure. When it does cause symptoms, you might notice painful or burning urination, discharge from the penis or vagina, lower abdominal pain, lower back pain, or pain during sex. Gonorrhea tends to appear faster, usually within 2 to 8 days but sometimes up to two weeks. Its hallmark is a thick, cloudy, or bloody discharge from the penis or vagina, along with burning urination and pelvic pain.
Trichomoniasis, caused by a parasite rather than bacteria, produces distinctive vaginal discharge that can be clear, white, greenish, or yellowish, often with a noticeable odor. It can also cause vaginal itching, burning, soreness, and pain during sex. Men with trichomoniasis sometimes have penile discharge or painful urination, but most men carry it without symptoms.
Sores, Blisters, and Ulcers
Genital herpes and syphilis both cause sores, but they look and feel quite different from each other.
Herpes sores typically start as small red bumps that develop into fluid-filled blisters, then break open into painful ulcers. They usually appear on or around the genitals, buttocks, or inner thighs, and they can make urination painful if the ulcers are near the urethra. The first outbreak is often the worst, sometimes causing severe ulcerations that last for weeks. Recurrent outbreaks are common with HSV-2 (the type most associated with genital herpes), though they tend to be less severe over time. HSV-1, better known for causing cold sores, can also infect the genitals but recurs less frequently.
Syphilis sores are a different story. In its primary stage, syphilis produces one or more sores called chancres at the site where the infection entered the body, usually on the genitals, rectum, tongue, or lips. These sores are firm, round, and painless, which means they’re easy to miss entirely. They heal on their own within three to six weeks, but the infection doesn’t go away. The incubation period ranges from 10 to 90 days, with an average of about 21 days.
Syphilis Has Multiple Stages
If syphilis goes untreated, it progresses to a secondary stage marked by skin rashes and sometimes sores in the mouth, vagina, or anus. The rash often appears on the palms of the hands or soles of the feet, looking rough, red, or reddish-brown. It usually doesn’t itch, and it can be faint enough to overlook. After this stage, syphilis enters a latent phase with no visible symptoms at all, but the infection remains in the body for years and can eventually cause serious damage to organs.
Warts and Growths
Human papillomavirus (HPV) is the STI behind genital warts. These appear as a small bump or cluster of bumps in the genital area. When several warts grow close together, they can take on a cauliflower-like shape. They may cause itching, discomfort, or bleeding during sex. Most HPV strains cause no symptoms at all, and the immune system clears many infections on its own. Certain high-risk HPV strains don’t cause warts but can lead to cervical, anal, or throat cancers years later, which is why screening matters even without visible signs.
Flu-Like Symptoms and HIV
About two-thirds of people newly infected with HIV develop flu-like symptoms within two to four weeks of exposure. These can include fever, chills, night sweats, muscle aches, sore throat, fatigue, swollen lymph nodes, mouth ulcers, and a rash. Symptoms can last anywhere from a few days to several weeks, then disappear. After this acute phase, HIV can remain in the body for years without causing noticeable illness, silently damaging the immune system.
Because these early symptoms look identical to a common flu or viral infection, most people don’t connect them to HIV exposure. Testing is the only reliable way to know.
Signs in the Throat and Rectum
STIs don’t only affect the genitals. Chlamydia and gonorrhea can infect the throat through oral sex and the rectum through anal sex, often without obvious symptoms. When rectal symptoms do appear, they include soreness, discharge, and bleeding. Syphilis chancres can form on the tongue, lips, or rectum. Herpes blisters can develop in or around the mouth.
These extragenital infections are easy to miss because people aren’t looking for STI signs in those locations, and standard urine-based tests won’t catch infections in the throat or rectum. If you’ve had oral or anal sex, testing at those specific sites is necessary for accurate results.
Who Should Get Tested and How Often
Because so many STIs are silent, routine screening is the most reliable way to catch infections early. The CDC’s screening guidelines recommend annual chlamydia and gonorrhea testing for all sexually active women under 25 and for women 25 and older with risk factors like new or multiple partners. Men who have sex with men should be tested for chlamydia, gonorrhea, and syphilis at least once a year, and every three to six months if they have multiple partners or are on PrEP.
All adults between ages 13 and 64 should be tested for HIV at least once. All adults over 18 should be screened for hepatitis C at least once. People living with HIV are recommended to screen for chlamydia, gonorrhea, syphilis, and trichomoniasis at their initial evaluation and at least annually after that.
Trichomoniasis screening is recommended for women in high-prevalence settings or those with risk factors like multiple partners or a history of other STIs. There’s no routine screening recommendation for herpes in people without symptoms, and HPV screening for women is handled through cervical cancer screening (Pap tests and HPV tests) rather than STI panels.
If you’re sexually active with more than one partner, or your partner has other partners, regular testing catches what symptoms alone never will.