STDs (Sexually Transmitted Diseases)

How are STDs caused and how to avoid them

Sexually transmitted diseases (STDs) — or sexually transmitted infections (STIs) — are generally acquired by sexual contact. The bacteria, viruses, or parasites that cause sexually transmitted diseases may pass from person to person in blood, semen, or vaginal and other bodily fluids.

Sometimes these infections can be transmitted nonsexually, such as from mothers to their infants during pregnancy.  It can be transmitted through even shared needles or blood transfusion.


STDs or STIs can be caused by:

  • Bacteria. Gonorrhea, syphilis, and chlamydia are examples of STIs that are caused by bacteria.
  • Parasites. Trichomoniasis is an STI caused by a parasite.
  • Viruses. STIs caused by viruses include HPV, genital herpes, and HIV.

Other kinds of infections — hepatitis A, B, and C viruses, shigella infection, and giardia infection — can be spread through sexual activity, but it’s possible to be infected without sexual contact.

Risk factors

Factors that may increase that risk includes:

  • Having unprotected sex
  • Having sexual contact with multiple partners
  • Having a history of STIs
  • Misuse of alcohol or use of recreational drugs
  • Injecting drugs


Signs and symptoms may appear a few days after exposure. However, it may take years before you have any noticeable problems, depending on the organism causing the STI.

Signs and symptoms that might indicate an STI include:

  • Sores or bumps on the genitals/in the oral/rectal area
  • Painful or burning urination
  • Discharge from the penis
  • Unusual or odorous vaginal discharge
  • Unusual vaginal bleeding
  • Pain during sex
  • Sore, swollen lymph nodes, particularly in the groin
  • Lower abdominal pain
  • Fever
  • A rash over the trunk, hands, or feet

See a doctor immediately if:

  • You are sexually active and may have been exposed to an STI
  • You have signs and symptoms of an STI

Make an appointment with a doctor:

  • When you’re considering becoming sexually active or when you’re 21 — whichever comes first
  • Before you start having sex with a new partner
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