Common Sexually Transmitted Infections (STIs)

Sexually transmitted infections (STIs) are infections that are spread by sexual contact. These infections are usually passed from person to person through vaginal intercourse. They can also be passed through anal sex, oral sex, or skin-to-skin contact. STIs can be caused by viruses, bacteria, or parasites. Many people get STIs but don’t know it because they don’t have any symptoms. Other people have symptoms that can be mild or more bothersome.

Path to improved health

There are many different kinds of STIs. Here is information on some of the most common ones, their symptoms, and their treatments.


What is it: Chlamydia is a bacterial infection that is easily cured. Left untreated it can cause infertility in women.

Symptoms:  Women may have pain when urinating, itching around the vagina, yellow fluid (discharge) from the vagina, bleeding between periods, or pain in the lower abdomen. Men may have a burning sensation when urinating and a milky colored discharge from the penis. It can also cause painful swelling of the scrotum in men.

Treatment: Antibiotics. Both partners should be treated.


What is it: Gonorrhea is a bacterial infection. Left untreated, it can cause serious health problems. But it is easily cured.

Symptoms:  Women may have white, green, yellow or bloody discharge from the vagina, pain when urinating, bleeding between periods, heavy bleeding during a period, or a fever. Both women and men can get sore throats if they’ve had oral contact with an infected person. Men may have thick, yellow discharge from the penis and pain when urinating. The opening of the penis may be sore. Gonorrhea can cause serious complications if it’s not treated.

Treatment: Antibiotics. Both partners should be treated.


What is it: Herpes is a viral infection that causes painful sores in the genital area. It is spread through skin-to-skin contact. Once you are infected, you have the virus for the rest of your life.

Symptoms: Women and men may have tingling, pain, or itching around the vagina or penis. They also may develop oral lesions (blisters) through sexual contact. Small blisters can form in these areas and then break open. When they break open, the sores can cause a burning feeling. It may hurt to urinate. Some people have swollen glands, fever, and body aches. The sores and other symptoms go away, but this does not mean that the virus is gone. The sores and blisters can come back periodically. This is called an “outbreak.”

Treatment: Medicine can treat symptoms but can’t cure herpes. If one partner is infected, the other should by checked by a doctor.


What is it: HIV (human immunodeficiency virus) is the virus that causes AIDS (acquired immunodeficiency syndrome). HIV attacks the body’s immune system, making you more likely to get sick from other viruses or bacteria.

Symptoms: HIV makes the body’s immune system weak so it can’t fight disease. Symptoms may take years to develop. When symptoms do appear, they can include swollen lymph nodes, diarrhea, fever, cough, shortness of breath, or unexplained weight loss. Symptoms are often similar to those of other illnesses, such as the flu.

Treatment: Medicines can treat symptoms but can’t cure HIV or AIDS. If one partner is infected, the other should be checked by a doctor.

HPV/Genital Warts

What is it: HPV (human papillomavirus) is a family of more than 100 types of viruses. Some don’t cause any symptoms. Some types cause genital warts. More aggressive types can cause cancer.

Symptoms: HPV can cause warts in or around the vagina, penis, or rectum. In women, the warts can be on the cervix or in the vagina where you can’t see them. Or they may be on the outside of the body, but may be too small to see. The warts can be small or large, flat or raised. They can appear singly or in groups. They usually don’t hurt. Most types of HPV, including those that cause cancer, do not have any symptoms.

Treatment: No medicine cures HPV. A doctor can remove external warts. Warts on the cervix or in the vagina can cause changes that may lead to cervical cancer. Doctors will watch for these changes. If one partner is infected with HPV, the other should be checked by a doctor.

Some types of HPV can be prevented, including those that cause cancer. There is a vaccine that can prevent some types of HPV in young men and women. The Centers for Disease Control and Prevention (CDC) recommends that girls and boys between the ages of 11 and 12 receive the vaccine, before they become sexually active. The vaccine is approved for men and women between the ages of 9 years and 26 years.

Pubic lice (crabs)

What is it: Public lice (also called crabs) are tiny insects that live in the pubic hair and lay eggs. They spread through direct contact but do not cause many problems.

Symptoms: Women and men may have redness and itching around the genitals. You may be able to see the lice or their eggs on the shaft of the pubic hair.

Treatment: Medicine, such as over-the-counter lotions or shampoos (some brand names: Nix, Rid), can kill the lice. Prescription shampoos, lotions, or pills are also available if over-the-counter medicine doesn’t work. Clothes, sheets, and towels must be washed in hot water to kill remaining bugs, or your lice can come back. Usually both partners need to be treated for pubic lice.


What is it: Syphilis is a serious bacterial infection that causes sores in the genital area. It is passed by touching the blood or sores of an infected person.

Symptoms: An early symptom is a red, painless sore, called a chancre. The sore can be on the penis, vagina, rectum, tongue, or throat. The glands near the sore may be swollen. Without treatment, the infection can spread into your blood. Then you may experience a fever, sore throat, headache, or pain in your joints. Another symptom is a scaly rash on the palms of the hands or the bottom of the feet. The sores and other symptoms go away, but this does not mean that the infection is gone. It could come back many years later and cause problems in the brain and spinal cord, heart, or other organs.

Treatment: Syphilis can cause serious health problems if it’s not treated. Antibiotics should be taken as early as possible after infection. If one partner is infected, the other should be tested.


What is it: Trichomoniasis is an infection caused by a parasite. The parasite spreads through skin-to-skin contact.

Symptoms: Women can have a heavy, greenish-yellow frothy discharge and pain when urinating or while having sex. It can also cause redness, itching, and a burning feeling in the genital area. Men may have burning with urination or ejaculation, itching or irritation inside the penis, or discharge from the penis. Left untreated, the infection can last for months or years.

Treatment: Antibiotics. Usually both partners need to be treated.

Things to consider

It’s common to feel guilty or ashamed when you are diagnosed with an STI. You may feel that someone you thought you could trust has hurt you. You may feel sad or upset. Talk to your family doctor about how you’re feeling. In many cases, the STI can be cured.

Remember that you can take steps to prevent getting an STI. The only sure way to prevent them is by not having sex. But if you do have sex, you can lower your risk.

  • Limit your number of sex partners.
  • Avoid sex with people who have had many sex partners.
  • Use condoms consistently and correctly.
  • Ask your partner if he or she has, or has had, an STI. Tell your partner if you have had one. Talk about whether you’ve both been tested for STIs and whether you should be tested.
  • Look for signs of an STI in your sex partner. But remember that STIs don’t always cause symptoms. Don’t have sex if you or your partner are being treated for an STI.
  • Wash your genitals with soap and water and urinate soon after you have sex. This may help clean away some germs before they have a chance to infect you.

Questions to ask your doctor

  • Do I have an STI? Can it be cured?
  • What kind of treatment will I need?
  • Can I have sex with my partner without passing on my STI?
  • Can I spread an STI if I don’t have symptoms and don’t even know I have it?
  • What can I do to prevent getting an STI?
  • If I am pregnant, can I pass my STI onto my baby?
  • Are there any STI support groups in my area?


U.S. National Library of Medicine, Sexually Transmitted Diseases

Centers for Disease Control and Prevention, Sexually Transmitted Diseases