STIs are some of the most difficult diseases to catch. You have to be up close and personal to spread them. So why are STIs so common? The answer may be that people don’t know how to recognize, treat, or prevent them. Or when they do, they often don’t do so effectively.

This article explores some of the most common sexually transmitted infections in the United States. It also discusses their causes and symptoms.

Not all diseases that affect the sex organs are considered STIs. In fact, some are not related to sex at all. Others aren’t transmitted during sex but occur as a result of it.

Here are some common STIs and diseases associated with sex, along with their symptoms.

Many women remain asymptomatic. When there are symptoms, they include pain during sex and discharge from the penis or vagina.

The Centers for Disease Control and Prevention (CDC) recommends that you be screened for chlamydia and other sexually transmitted infections if you are under 25 years old and sexually active. The CDC also recommends screening if you have any of these risk factors:

You have a new sex partner. You have a sex partner with an STI. You have more than one sex partner. You have a sex partner who is having sex with other people.

Chlamydia can do a lot of damage to your body in the long run. It can cause infertility by blocking the reproductive tract in men and women. Latex condoms can prevent the spread of this disease.

If you have gonorrhea, you may experience a burning sensation when you urinate. The disease can also cause white, yellow, or green discharge from the penis or vagina. It’s important to know that many people, especially women, with gonorrhea don’t have symptoms.

Be aware, too, that gonorrhea can also infect your throat if you get it by having oral sex.

Gonorrhea does not always go away when it’s treated by antibiotics. There is a growing problem of antibiotic-resistant gonorrhea, which means it no longer dies off with antibiotic drugs that used to kill it.

Syphilis is transmitted when you come into direct contact with syphilis sores, which are usually found on the outside or inside of sex organs. They can also appear on your mouth or rectum.

That means it can be transmitted by oral, vaginal, or anal sex. In fact, some scientists think that oral sex is responsible for the rise of syphilis in men who have sex with men.

At first, syphilis sores (ulcers called chancres) are small and painless. They may heal by themselves, but that doesn’t mean the disease is gone. It’s just become harder to spot and treat.

MG can cause the same kinds of symptoms as gonorrhea and chlamydia. In 2007, a well-known study of U.S. teens found that MG infected more people than gonorrhea.

Why did it take so long to recognize MG’s importance? Because most cases don’t cause symptoms. It was hard to identify until new technology became available. Microbiologic testing is the diagnostic tool of choice for detection of M. genitalium. These are called NAATs (Nucleic Acid Amplification Tests). In the United States, two NAATs have been cleared by the Food and Drug Administration (FDA) for this purpose.

Frothy discharge Strong vaginal odor Pain during intercourse Irritation Itching

Men with trichomoniasis don’t usually have symptoms. If you have been diagnosed with the disease, make sure your partner gets treated. Even if trichomoniasis does not seem to be affecting your partner much, they can still give it back to you, no matter what their sex.

HPV is sometimes called “the cervical cancer virus,” but only a few types of HPV can cause cancer. There are other cancers linked to HPV, including penile and anal cancer. Other HPV types cause genital warts, other warts, or no symptoms at all.

There is no cure for HPV, but its symptoms can be treated. Infections can sometimes resolve on their own. It is recommended that 11- to 12-year-olds get the HPV vaccine to protect them from the most common strains of the virus.

Herpes cannot be cured. But its symptoms can be treated with antiviral drugs. You can pass the virus to someone else even if you do not have any sores or other symptoms.

Using a condom lowers the risk of spreading herpes. You can still get herpes even if you use a condom, though.

SemenVaginal fluidsBreast milkBlood

HIV cannot be passed by casual contact.

Today, most people with HIV are treated with a combination of drugs known as highly active antiretroviral therapy (HAART), or combined antiretroviral therapy (cART). These therapies cannot cure the disease, but they can reduce the chances of HIV leading to AIDS.

Over time, hepatitis B and C can lead to scarring of the liver, cirrhosis, and liver cancer. Fortunately, there is a vaccine that can protect you from hepatitis B. The hepatitis B vaccine is recommended for all infants and children and many groups of adults—however, anyone who wants to be protected can get it. While there isn’t a vaccine for hepatitis C, there are very effective treatments that can cure the infection.

Some people question whether BV is an STD, but there is a link between BV and having a new sex partner or multiple sex partners. You can take antibiotics to get rid of BV, but it can show up again.

The ulcers caused by chancroid are often larger than those caused by syphilis. They can be more painful, too. Early on, it can be hard to tell these two infections apart.

In 2003, an LGV outbreak happened among men who have sex with men (MSM) in the Netherlands. Since then, it has been found in some groups of MSM across western Europe, North America, and Australia.