Sexually transmitted infections (STIs) are also called sexually transmitted diseases (STDs). Aside from colds and the flu, STDs are some of the most widespread infections both in the United States and the world. STDs affect both men and women, and almost half of all STDs occur in people younger than 25 years old. Exposure to an STD can occur any time you have sexual contact with anyone that involves the genitalscamera, the mouth (oral), or the rectum (anal). Exposure is more likely if you have more than one sex partner or do not use condoms. Some STDs can be passed by nonsexual contact, such as by sharing needles or during the delivery of a baby or during breast-feeding.

STDs are a worldwide public health concern because there is more opportunity for STDs to be spread as more people travel and engage in sexual activities. Some STDs have been linked to an increased risk of certain cancers and infection with human immunodeficiency virus (HIV). Pregnant women can spread STDs to their babies. Many people may not have symptoms of an STD but are still able to spread an infection. STD testing can help find problems early on so that treatment can begin if needed. It is important to practice safe sex with all partners, especially if you or they have high-risk sexual behaviors. See the Prevention section of this topic.

If you think you may have symptoms of an STD:

Do not have sexual contact or activity while waiting for your appointment. This will prevent the spread of the infection. Women should not douche. Douching changes the normal balance of bacteria in the vagina. Douching may flush an infection up into your uterus or fallopian tubes and cause pelvic inflammatory disease (PID).

Common sexually transmitted infections
There are at least 20 different STDs. They can be caused by viruses, bacteria, and protozoa. Some of the most common STDs in the U.S. are:

• Chlamydia.
• Genital herpes.
• Genital warts or human papillomavirus (HPV). Certain high-risk types of HPV can cause cervical cancer in women.
• Gonorrhea.
• Hepatitis B.
• Syphilis.
• Trichomoniasis.
• Human immunodeficiency virus (HIV), which causes AIDS. Having other STDs, such as genital herpes, can increase your risk of HIV.
• Other infections that may be sexually transmitted. These include hepatitis A, cytomegalovirus, molluscum contagiosum, Mycoplasma genitalium, hepatitis C, and possibly bacterial vaginosis.
• Scabies and pubic lice, which can be spread by sexual contact.

Bacterial STDs can be treated and cured, but STDs caused by viruses usually cannot be cured. You can get a bacterial STD over and over again, even if it is one that you were treated for and cured of in the past.
Sexually active teens and young adults Sexually active teenagers and young adults are at high risk for STDs because they have biological changes during the teen years that increase their risk for getting an STD and they may be more likely to:

• Have unprotected sex.
• Engage in high-risk sexual behaviors.
• Have partners who have high-risk sexual behaviors.

Studies show:
Sexually active teens and young adults:

• Ages 15 to 24 years old get almost half of all new STDs each year.
• Have the highest rates of chlamydia and gonorrhea.
• About 1 out of 5 women and 1 out of 9 men get genital herpes, and it is more common in women than in men.
•  As many as half of all sexually active men and women have been infected with genital types of human papillomavirus (HPV) at some time in their lives.
• Syphilis rates have increased.
• New HIV infections have increased in people ages 13 to 29.

It is important to seek treatment if you think you may have an STD or have been exposed to an STD. Most health departments, family planning clinics, and STD clinics provide confidential services for the diagnosis and treatment of STDs. Early treatment can cure a bacterial STD and prevent complications.

If you are a parent of a teenager, there are many resources available, such as your health professional or family planning clinics, to help you talk with your teen about safe sex, preventing STIs, and being evaluated and treated for STDs.
Risks specific to women with sexually transmitted infections

In women, STDs can cause a serious infection of the uterus and fallopian tubes (reproductive organscamera) called pelvic inflammatory disease (PID). PID may cause scar tissue that blocks the fallopian tubes, leading to infertility, ectopic pregnancy, pelvic abscess, or chronic pelvic pain.

STDs in pregnant women may cause problems such as:

• Miscarriage.
• Low birth weight.
• Premature delivery.
• Infections in their newborn baby, such as pneumonia, eye infections, or nervous system problems.
• Risks specific to men with sexually transmitted infections.
• Infection and inflammation of the epididymis, urethra, anus, and prostate

Any child or vulnerable adult with symptoms of an STD needs to be evaluated by a health professional to determine the cause and to assess for possible sexual abuse. If you have symptoms of an STD or have been exposed to an STD whether by oral, anal, or vaginal sexual activity, use the Check Your Symptoms section to decide if and when you should see a doctor.