Chlamydia

About it: chlamydia is a bacterial infection and the most common STD in the U.S. It is contracted through sexual contact with an infected person.

Signs and symptoms: many people with chlamydia experience no symptoms at all. The ones who have symptoms report feeling a burning sensation during urination, genital discharge, tenderness of the testes in men and painful intercourse.{relatedarticles}

Treatment: if left untreated, chlamydia can cause serious health issues, often developing into pelvic inflammatory disease, or PID, in women. Chlamydia can be treated and cured with a regimen of antibiotics.

HIV/AIDS

About it: HIV, or human immunodeficiency virus, is a deadly virus that attacks a person's immune system. Eventually, HIV develops into AIDS (acquired immunodeficiency syndrome) in which the body's immune system no longer can fight off bacteria or viruses.

HIV cannot be passed through simple contact. It can only be passed on through the exchange of fluids, such as blood, semen or vaginal secretions, through needle sharing, or in the case of an infant, through childbirth or breast milk.

Signs and symptoms: often, there are no early symptoms of HIV. When there are, they usually include diarrhea, night sweats, weight loss, swollen glands, fever and other flu-like symptoms.