Sexually transmitted diseases (STDs) are infections acquired by sexual contact. You can catch sexually transmitted diseases any time you have unprotected sex with a partner who is already infected.

What is it?

Sexually transmitted diseases (STDs) are infections acquired by sexual contact. You can catch sexually transmitted diseases any time you have unprotected sex with a partner who is already infected. The organisms that cause sexually transmitted diseases may pass from person to person in blood, semen or vaginal fluids.

It's possible to contract sexually transmitted diseases from people who seem perfectly healthy — people who, in fact, aren't even aware of being infected. That's because many sexually transmitted diseases cause no symptoms, at least at first. The symptoms of several sexually transmitted diseases are also easy to mistake for those of other conditions, so the correct diagnosis may be delayed.


Sexually transmitted diseases have a wide range of symptoms. The signs and symptoms listed here are the most common, but they occur in different combinations with different infections. The timelines from infection to symptoms — and from initial infection to advanced disease — also vary from disease to disease.

The first signs and symptoms of some STDs, occurring shortly after you're exposed to a sexually transmissible agent, are known as primary or acute infection.

Primary infection symptoms

  • May go unnoticed
  • A sore or a cluster of sores or bumps, with or without pain, on the genitals or in the oral or rectal area
  • Painful or burning urination
  • Discharge from the penis
  • Vaginal discharge
  • Unusual vaginal bleeding
  • Sore, swollen lymph nodes, particularly in the groin but sometimes more widespread
  • Fever and other flu-like symptoms
  • Appear a few days to three months after exposure, depending on the organism
  • May be attributed to a noninfectious cause, such as a cold, fatigue or skin irritation
  • May resolve in a few weeks, even without treatment, but progression with later complications — or recurrence — usually occurs (Transmission of some STDs may still be possible during this period.)

Advanced disease: Months to years after primary infection

  • Sores or bumps anywhere on the body
  • Recurrent genital sores
  • Generalized skin rash
  • Pain during intercourse
  • Scrotal pain, redness and swelling
  • Pelvic pain
  • Groin abscess
  • Infections associated with human immunodeficiency virus (HIV)
  • Infertility
  • For some infections, neurological or cardiovascular problems
  • Cancer


More than 30 viruses, bacteria and parasites cause STDs. Many of these organisms rely almost completely on sexual transmission to survive. In other words, if you have one of these infections, you most likely got it from sexual contact. The microbes include:

  • Bacteria that cause gonorrhea (Neisseria gonorrhea)
  • Bacteria that cause syphilis (Treponema pallidum)
  • Bacteria that cause urethritis, cervicitis and pelvic inflammatory disease (Chlamydia trachomatis)
  • Bacteria and intestinal parasites that cause rectal and anal pain, sometimes with severe diarrhoea
  • Single-celled organisms that cause urethritis, vaginitis, cervicitis and pelvic inflammatory disease (Trichomonas vaginalis)
  • Viruses that cause cervical and anal cancer (human papillomavirus, also known as HPV, types 16, 18, 31, 33, 45, 52 and 58)
  • Viruses that cause genital herpes (herpes simplex virus, also known as HSV, usually type 2 but sometimes type 1)

Sexual activity plays a role in spreading many other infectious agents, although it's possible to catch these infections without sexual contact. Viruses capable of spreading both sexually and through close nonsexual contact include the Epstein-Barr virus — responsible for mononucleosis — and a related virus called cytomegalovirus. Hepatitis A, a viral infection usually contracted from contaminated food and water, sometimes passes between sex partners, mainly men who have sex with men. The same pattern of transmission occurs with several common food- and water-borne bacteria and parasites, including shigella, cryptosporidium and Giardia lamblia.

Intravenous drugs abusers have a high risk of HIV and hepatitis B, which spread through needle sharing as well as sex.

Risk factors

Even between faithful and committed partners, STDs can happen. It's possible to be infected with herpes, for example, and never realize it, then pass the infection to your long-term partner. More often, though, people get sexually transmitted infections from casual or new partners.

Your risk of catching any STD depends on your sex, age and sexual practices, as well as on the sexual practices and lifestyles of your potential partners. The same factors determine which STDs you're most likely to be exposed to.

General risk factors include:

  • Being sexually active. Some activities carry a high risk of transmitting infection. The riskiest activities are anal and vaginal intercourse.
  • Starting sexual activity at an early age. The possibility of catching an STD or becoming pregnant doesn't seem real to many adolescents. If they worry about risk at all, they do so after having sex. Also, the younger you start, the more partners you may have.
  • Having high-risk sex. Vaginal or anal penetration by an infected partner who is not wearing a latex condom transmits some diseases with frightening efficiency. Without a condom, a man who has gonorrhea has a 70 to 80 percent chance of infecting his female partner in a single act of vaginal intercourse. Oral sex is less risky but still too dangerous to chance without a latex condom or dental dam.
  • Currently having an STD. Being infected with one STD makes it much easier for another STD to take hold. If you're infected with herpes, syphilis, gonorrhea or chlamydia and you have unprotected sex with an HIV-positive partner, you're more likely to contract the virus.
  • Having a history of an STD. If you've had one STD, you're at increased risk of catching another one, partly because you and your potential sex partners often belong to social networks made up of people of similar age, location and background. Within these overlapping networks, couples regularly form, split up and find new partners. If one STD is making its way through such a network, there's a good chance that others are, too.
  • Having multiple sex partners, not just concurrently but over time. Every time you break up with one partner and move on to another, even if each relationship is monogamous, your STD risk is increased.
  • Using alcohol or recreational drugs. These habits lower your inhibitions and impair your judgment, so you're more likely to take sexual risks.
  • Injecting drugs. Needle-sharing spreads many dangerous infections, including HIV and hepatitis B. If you acquire HIV by injecting drugs, you can transmit it sexually.
  • Being young. Almost half of the new cases of STDs each year are in people between the ages of 15 and 24 years.
  • Being female. At all ages, women are more likely to have severe STD complications, such as infertility, than are men. In teenage girls and young adult women, the cervix is made up of constantly changing cells. These unstable cells make the cervix more vulnerable to certain sexually transmitted organisms, so vaginal intercourse poses added risks.
  • Being African-American. STDs, particularly gonorrhea and syphilis, are reported in a disproportionate number of African-Americans. This may be partly because African-Americans are more likely to receive care at clinics that report STD statistics, including breakdowns of cases by age, sex and race.
  • Having sex with men. Whether you're male or female, male sex partners are riskier. For women, having vaginal intercourse or performing oral sex on a man without a latex condom is a high-risk activity. Homosexual men are also at increased risk of STDs, as are male and female sex workers and their customers. Some men who have heterosexual relationships also engage in clandestine sex with other men, posing risks to themselves and their partners of both sexes.
  • Meeting people in public places or online for sex. Casual, anonymous sex promotes the spread of STDs across social networks and different demographic groups.


Prompt treatment prevents the complications of some STDs. Unfortunately, you may not notice the symptoms of primary infection, which is the easiest to treat. Possible complications include:

  • Arthritis
  • Eye inflammation
  • Pelvic inflammatory disease
  • Infertility
  • Cervical cancer
  • Other cancers, including HIV-associated lymphoma and HPV-associated rectal and anal cancers
  • Opportunistic infections occurring in advanced HIV
  • Heart disease
  • Difficulty walking or maintaining balance
  • Personality change
  • Memory loss
  • Maternal-fetal transmission, which causes severe birth defects


If your sexual history and current signs and symptoms suggest that you have an STD, laboratory tests can identify the cause and detect co-infections you might also have contracted.

Blood tests confirm the diagnosis of most viral STDs. If you have active herpes sores, however, testing fluid and scrapings from the sores is simpler and less expensive than is testing blood.

Laboratory tests of material from a genital sore or discharge are used to diagnose the most common bacterial STDs at an early stage. Chlamydia may go unnoticed at this stage in both men and women, though, delaying the diagnosis until complications such as pelvic inflammatory disease (PID) occur. Women can easily miss the symptoms or signs of gonorrhea as well.