STDs are infectious diseases passed from person to person through sexual contact. Millions of new cases happen every year in the U.S. Half of the new infections happen in people between the ages of 15 and 24 years.

How can you protect yourself from STDs?

The best way to prevent getting an STD is to not have any type of sexual activity, including oral, vaginal, and anal sex. But you can take several steps to lower your risk for an STD if you decide to become sexually active, or are currently sexually active. These include:

• Any sexual relationship should be with only one uninfected partner. That partner should also not have any other partners.

• Use a latex condom the correct way every time you have sex. Or use a female polyurethane condom plus medicine that kills sperm (topical microbicide).

• Use sterile needles if you inject IV medicines.

• Prevent and control other STDs. This will lower your risk for human papillomavirus (HPV).

• Delay having sexual relationships as long as you can. The younger you are when you start having sex, the more likely you are to get an STD.

• Have regular checkups for HIV and STDs.

• Learn the symptoms of STDs and seek medical help as soon as possible if any symptoms develop.

• Don't have sexual intercourse during your monthly period.

• Don't have anal intercourse. Or use a latex condom and medicine that kills sperm.

• Don't douche.

Some people may get help in preventing HIV infection by taking a special medicine (pre-exposure prophylaxis). Talk with your healthcare provider to see if it is right for you.

What to do when diagnosed with an STD?

• Begin treatment right away. Take the full course of medicines, and follow your healthcare provider's advice.

• Don't breastfeed a baby or use breastmilk to feed a baby if you are HIV positive.

• Tell your local health department or all recent sexual partners and urge them to get medical checkups.

• Don't have sexual activity while getting treatment for an STD.

• Have a follow-up test to be sure the STD has been successfully treated.

What are some common types of STDs?

Common STDs are listed below.

HIV

HIV is a virus that destroys the body's ability to fight off infection. People who have HIV may not look or feel sick for a long time after infection. But if you are not diagnosed early and treated, you will eventually become very likely to get many life-threatening diseases and certain forms of cancer. The virus is passed on most often during sexual activity. It can also be passed on by sharing needles used to inject IV drugs. HIV can be passed to your baby during pregnancy, labor, delivery, and through breastfeeding. If you know early in your pregnancy that you are HIV positive, you can get treatment that greatly lowers your chance of passing on the virus to your child, the CDC says.

Human papillomavirus (HPV)

HPV is a common sexually transmitted disease. Some types of HPV can cause genital warts (condylomas). These can happen on the inside or outside areas of the genitals. They may spread to the surrounding skin or to a sexual partner. Many other types of HPV cause no symptoms, so you may not know that you are infected. In most cases, the virus goes away and does not cause further health problems. But if the virus lasts, normal cells can change and become abnormal. Women with an HPV infection with high-risk types like HPV 16 and 18 have an increased risk of getting cervical cancer. Pap tests can detect HPV infection, as well as abnormal cervical cells. An HPV vaccine protects against the types of HPV that cause most cervical cancers. It also protects against most genital warts in both men and women, and against anal cancer in men. Even with treatment for genital warts, the virus remains in the body and warts can reappear. Certain types of HPV can also cause warts on other body parts such as the hands. These are called common warts. These don't generally cause health problems. If a pregnant woman has a large number of genital warts, the growths can complicate a vaginal delivery. If the warts block the birth canal, the woman may need a cesarean section.

Chlamydia

Chlamydia is the most commonly reported STD in the U.S. It can affect both men and women. This infection may cause an abnormal genital discharge and burning with urination. In women, untreated chlamydia may lead to pelvic inflammatory disease (PID). Chlamydia can be treated with antibiotics. Unfortunately, many people with chlamydia have few or no symptoms of infection. The most common and serious complications occur in women. In addition to PID, these include tubal (ectopic) pregnancy and infertility. Chlamydia can also be carried in and affect the rectum. If you are pregnant and have chlamydia, the infection can be passed to your baby at birth. This can cause eye infections or pneumonia in your baby. With chlamydia, you are also more likely to have your baby too early.

Gonorrhea

Gonorrhea causes a discharge from the vagina or penis and painful or difficult urination. The most common and serious complications happen in women. They include PID, tubal pregnancy, and infertility. Gonorrhea can be treated with antibiotics. Gonorrhea can also be carried in and affect the rectum. Gonorrhea at the time of childbirth can spread to the baby and cause severe eye infection.

Genital herpes

Genital herpes infections are caused by the herpes simplex virus (HSV). Symptoms may include painful blisters or open sores in the genital area. Tingling or burning sensation in the legs, buttocks, or genital area may happen just before the blisters show up. The herpes sores usually disappear within a few weeks. The virus stays in the body, and the sores may return from time to time. There is no cure for HSV, but medicine can shorten an outbreak and reduce symptoms. HSV can be passed on from the mouth to the genitals during oral sex. The virus can be passed on to sexual partners even if the person has no visible blisters. This is called asymptomatic shedding. HSV can also be spread to a baby at the time of childbirth. This causes a very severe infection in the infant.

Syphilis

The first symptom of syphilis is a painless open sore that usually shows up on the penis, in the vagina, or on the skin around either sexual organ. Untreated syphilis may go on to more advanced stages. These include a rash and over time problems with the heart and central nervous system. Syphilis can be treated with antibiotics. If a pregnant woman has untreated syphilis, the disease can cause dangerous, even fatal, problems for the baby. The way congenital syphilis affects the infant depends on how long the woman has had the disease and if or when she was treated for the infection. This form of syphilis can cause miscarriage, stillbirth, or death of the baby shortly after birth. According to the CDC, about 2 in 5 babies born to women with untreated syphilis may be stillborn or die from the infection in infancy.

Other diseases

Other diseases that may be sexually transmitted include:

• Bacterial vaginosis

• Chancroid

• Cytomegalovirus infections

• Granuloma inguinale (donovanosis)

• Lymphogranuloma venereum

• Molluscum contagiosum

• Pubic lice

• Scabies

• Trichomoniasis

• Vaginal yeast infections

What are the facts about STDs and teens?

STDs affect men and women of all backgrounds and economic levels. But nearly half of all STD cases in the U.S. happen in people younger than age 25.

STDs are on the rise. This may be because more sexually active people have multiple sex partners during their life.

Many STDs cause no symptoms at first. Also, many STD symptoms may look like those of other diseases not transmitted through sexual contact. This is especially true in women. Even STDs without symptoms can be spread to other people.

Women suffer more severe symptoms from STDs:

• Some STDs can spread into the womb (uterus) and fallopian tubes and cause PID. This can lead to both infertility and tubal pregnancy.

• STDs in women also may lead to cervical cancer.

• STDs can be passed from a mother to her baby before or during birth. Some infections of the newborn may be successfully treated. Others may cause a baby to be permanently disabled or even die.

Many STDs can be successfully treated when diagnosed early.