<meta http-equiv="refresh" content="1; url=/nojavascript/"> Sexually Transmitted Infections | CK-12 Foundation
Skip Navigation
You are reading an older version of this FlexBook® textbook: CK-12 Life Science Concepts For Middle School Go to the latest version.

11.77: Sexually Transmitted Infections

Difficulty Level: At Grade Created by: CK-12
 0  0  0
Best Score
Practice Sexually Transmitted Infections
Best Score
Practice Now

What is safe sex?

Safe sex is sexual activity engaged in by people who have taken precautions to protect themselves against sexually transmitted diseases. Abstaining from sexual activity, however, is the only way to be absolutely sure that you won't get a sexually transmitted disease.

Sexually Transmitted Diseases

A sexually transmitted disease (STD) is a disease that spreads through sexual contact. STDs are caused by pathogens , a living thing or virus that causes disease. The pathogens enter the body through the reproductive organs. Many STDs also spread through body fluids, such as blood. For example, a shared tattoo needle is one way an STD could spread. Some STDs can also spread from a mother to her baby during childbirth.

STDs are more common in teens and young adults than in older people. One reason is that young people are more likely to take risks. They also may not know how STDs spread. They are likely to believe myths about STDs, like the myths in Table below .

Myth Fact
If you are sexually active with just one person, you can’t get STDs. The only way to avoid the risk of STDs is to practice abstinence from sexual activity.
If you don’t have any symptoms, then you don’t have an STD. Many STDs do not cause symptoms, especially in females.
Getting STDs is no big deal, because STDs can be cured with medicine. Only some STDs can be cured with medicine; other STDs cannot be cured.

Most STDs are caused by bacteria or viruses. STDs caused by bacteria usually can be cured with drugs called antibiotics. But antibiotics are not effective against viruses. Therefore, STDs caused by viruses are not treated with antibiotics. Other drugs may be used to help control the symptoms of viral STDs, but they cannot be cured. Once you have a viral STD, you are usually infected for life.

Bacterial STDs

In the U.S., chlamydia is the most common STD caused by bacteria. Females are more likely than males to develop the disease. Rates of chlamydia among U.S. females in 2006 is given in Figure below . Rates were much higher in teens and young women than in other age groups.

Chlamydia may cause a burning feeling during urination. It may also cause a discharge (leaking of fluids) from the vagina or penis. But in many cases it causes no symptoms. As a result, people do not know they are infected, so they don’t go to the doctor for help. If chlamydia goes untreated, it may cause more serious problems in females. It may cause infections of the uterus, Fallopian tubes, or ovaries. These infections may leave a woman unable to have children.

This graph shows data on the number of cases of chlamydia in U.S. males and females in 2009. Which two age groups had the highest rates of chlamydia? Why do you think rates were highest in these age groups?

Gonorrhea is another common STD. Gonorrhea may cause pain during urination. It may also cause a discharge from the vagina or penis. On the other hand, some people with gonorrhea have no symptoms. As a result, they don’t seek treatment. Without treatment, gonorrhea may lead to infection of other reproductive organs. This can happen in males as well as females.

Syphilis is a very serious STD. Luckily, it is less common than chlamydia or gonorrhea. Syphilis usually begins with a small sore on the genitals. This is followed a few months later by a rash and flu-like symptoms. If syphilis is not treated, it may damage the heart, brain, and other organs. It can even cause death.

Viral STDs

Genital warts are an STD caused by human papilloma virus, or HPV . They are one of the most common STDs in teens. HPV infections cannot be cured. But a new vaccine called Gardasil® can prevent most HPV infections in females. Many doctors recommend that females between the ages of 9 and 26 years receive the vaccine. Preventing HPV infections in females is important because HPV can also cause cancer of the cervix.

A related herpes virus causes cold sores on the lips ( Figure below ). Both viruses cause painful blisters. In the case of genital herpes , the blisters are on the penis or around the vaginal opening. The blisters go away on their own, but the virus remains in the body. The blisters may come back repeatedly, especially when a person is under stress. There is no cure for genital herpes. But drugs can help prevent or shorten outbreaks. Researchers are trying to find a vaccine to prevent genital herpes.

This lip blister, or cold sore, is caused by a herpes virus. The virus is closely related to the virus that causes genital herpes. The genital herpes virus causes similar blisters on the genitals. If you’ve ever had a cold sore, you know how painful they can be. Genital herpes blisters are also painful.

Hepatitis B is a disease of the liver. It is caused by a virus called hepatitis B, which can be passed through sexual activity. Hepatitis B causes vomiting. It also causes yellowing of the skin and eyes. The disease goes away on its own in some people. Other people are sick for the rest of their lives. In these people, the virus usually damages the liver. It may also lead to liver cancer. Medicines can help prevent liver damage in these people. There is also a vaccine to protect against hepatitis B.

HIV stands for "human immunodeficiency virus." It is the virus that causes AIDS. HIV and AIDS are described in a previous lesson. HIV can spread through sexual contact. It can also spread through body fluids such as blood. There is no cure for HIV infection, and AIDS can cause death, although AIDS can be delayed for several years with medication. Researchers are trying to find a vaccine to prevent HIV infection.


  • chlamydia : Sexually transmitted bacterial infection; the most common STD caused by a bacteria.
  • genital herpes : Sexually transmitted infection caused by a herpes virus; characterized by periodic outbreaks of blisters on the genitals.
  • gonorrhea : Common sexually transmitted infection caused by bacteria.
  • hepatitis B : Inflammation of the liver caused by infection with hepatitis B virus; often transmitted through sexual contact.
  • HIV : Human immunodeficiency virus; virus that causes AIDS.
  • HPV : Sexually transmitted virus that causes genital warts and cervical cancer.
  • pathogen : A living thing or virus that causes disease.
  • sexually transmitted disease (STD) : Infection caused by a pathogen that spreads mainly through sexual contact.
  • syphilis : Sexually transmitted infection caused by bacteria that may eventually be fatal if untreated.


  • Sexually transmitted diseases (STDs) are caused by pathogens. They spread through sexual contact or other exchanges of body fluids.
  • Examples of STDs caused by bacteria include chlamydia, gonorrhea, and syphilis.
  • Examples of STDs caused by viruses include HPV, genital herpes, hepatitis B, and AIDS.


Use the resource below to answer the questions that follow.

  1. How many cases of sexually transmitted diseases occur in the United States every year?
  2. What can untreated chlamydial and gonococcal infection lead to? How can this have long term effects on people?
  3. What does HPV cause?
  4. Why might living in an urban area increase a person's chance of contracting a sexually transmitted disease? Do you think this situation is different for non-sexually transmitted disease? Explain your reasoning fully.
  5. What are some ways to minimize the risk of contracting a sexually transmitted disease?


  1. It is especially important for females to be protected from HPV infections. Why is this the case?
  2. Explain why bacterial STDs are treated differently than viral STDs.

Image Attributions


Difficulty Level:

At Grade


7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Oct 04, 2014
Files can only be attached to the latest version of Modality


Please wait...
Please wait...
Image Detail
Sizes: Medium | Original
ShareThis Copy and Paste

Original text