Common Sexually Transmitted Infections

Each of the most common STIs has particular distinguishing characteristics. A clinician will keep these characteristics in mind when formulating a diagnosis. Here is a breakdown of the signs, symptoms, and risks of specific STIs.

Human papillomavirus (HPV)

Human papillomavirus infections (also known as “HPV”) are the most common STIs in the United States, affecting 42 million Americans. When a person becomes infected with HPV, their immune system is typically able to clear the virus on its own after a few months. When the virus does not go away on its own, it can cause larger health problems.

Certain strains of the HPV virus have been associated with cancer development (most commonly cervical cancer), so it is important to detect and treat HPV infections that do not clear on their own.

HPV usually does not cause any symptoms in its host. If a person does have symptoms of HPV, they usually present as genital warts. These warts can look like various-sized single bumps, a collection of bumps, or classically, like a cauliflower. A clinician can usually identify HPV genital warts during a physical exam.

Herpes simplex virus

Genital herpes infections represent the second most common STI in the United States. These infections are caused by one of two types of the herpes virus; type 1 (HSV-1) or type 2 (HSV-2).

Genital herpes often does not cause any symptoms. It can be so easily spread from one person to another during sexual activity. When symptoms are present, they can range from an itching sensation to a cluster of painful or burning ulcers.

Risks of a genital herpes infection include recurrence (often a first outbreak is followed by subsequent flares, as the virus lives in the body’s nerves cells forever), rashes on other parts of the body, serious brain infections, or transmission of the virus to a fetus during pregnancy or to a baby during childbirth.


Chlamydia is a bacterial infection that is spread from vaginal, anal, or oral sex. Many people may not know that they have chlamydia because it does not always cause symptoms. If symptoms do occur, they may include abnormal vaginal or penile discharge, burning with urination, pelvic pain, testicular pain, or rectal pain.

Risks of untreated chlamydia include developing a condition known as a pelvic inflammatory disease (PID). Chlamydia can also impair a women’s ability to get pregnant in the future, and it can lead to ectopic pregnancies (pregnancies that occur outside of the uterus and can be fatal). Women who are pregnant can transmit chlamydia to a baby during childbirth, potentially causing infection.


Gonorrhea is a bacterial infection that can be spread during vaginal, anal, or oral sex. In women, gonorrhea generally does not cause symptoms. If they have symptoms, women may experience burning with urination, abnormal vaginal discharge, or abnormal vaginal bleeding. Men with gonorrhea infections may experience burning with urination, as well as penile discharge or testicular pain or swelling.

If gonorrhea is left untreated, it can cause pelvic inflammatory disease (PID), fertility problems, ectopic pregnancies, chronic pain, or infections in other places in the body, such as the joints. Women who are pregnant can transmit gonorrhea to a baby during childbirth, potentially causing a serious infection.


Trichomoniasis is a sexually transmitted infection caused by a parasite known as Trichomonas vaginalis, and it is the most common curable STI in the United States, according to the US Centers for Disease Control and Prevention (CDC). Trichomoniasis is transmitted during vaginal-penile or vaginal-vaginal sexual activity.

Like chlamydia and gonorrhea, many people who have trichomoniasis have no symptoms, so they are unaware that they have an infection. If symptoms are present, they may include burning with irritation, genital burning or irritation, itching, odor, or abnormal vaginal or penile discharge.

A trichomoniasis infection can make it easier for a person to contract other STIs. In pregnant women, it can increase the risk of having a preterm or low birth weight baby.


Syphilis is a bacterial infection that can be spread during vaginal, anal, or oral sex. Some people may not notice the first symptom of syphilis, a flat, painless sore that occurs in the place of infection (genitals, anus, or mouth) and goes away on its own after a few weeks. If syphilis is not treated during this first stage, it can advance to a second stage, including a rash, lymph node enlargement, tiredness, or fever.

This stage can also be mild and, because it resolves on its own, it may also go unnoticed and untreated. However, the last stage of syphilis (“tertiary syphilis”), which can occur after many years of asymptomatic disease, can cause severe brain, eyes, heart, blood vessels, and other places in the body. Syphilis can also cause problems when it is spread from a mother to a fetus during pregnancy or a baby during childbirth.


HIV, also known as the human immunodeficiency virus, is spread from vaginal or anal sex and blood contact. When HIV progresses to a certain stage, it causes the acquired immunodeficiency syndrome (AIDS). Pregnant women can spread AIDS to a baby during pregnancy, childbirth, or breastfeeding.

The symptoms of HIV can be very subtle and may not be noticed by a person infected with the virus. When people do have signs of an initial HIV infection, they can include flu-like symptoms such as fever, chills, sore throat, night sweats, rashes, muscle pain, tiredness, or lymph node enlargement.

The major risk posed by HIV is its effect on the immune system. If left untreated, HIV can progress to a stage where the body’s immune cells are very suppressed, leaving a person vulnerable to “opportunistic infections.” An opportunistic infection is one that a healthy immune system can easily combat. Still, a suppressed immune system cannot fight effectively. Untreated, AIDS can be fatal. However, because of the effective medications available for HIV treatment, many people with HIV will never develop AIDS.