Sexually transmitted infections (STIs) usually pass from one person to another through sexual contact. Examples include chlamydia, crabs, and genital herpes. Treatment depends on the type of STI.

HIV has other routes of transmission. For example, it can spread through the use of unsterilized drug needles as well as sexual contact.

STIs can affect anyone. Many STIs can spread through nonpenetrative sexual activity.

This article looks at some common STIs, how to prevent them, and when to seek help.

condoms help prevent sexually transmitted infectionsShare on Pinterest
pederk/Getty Images

Chlamydia results from an infection with Chlamydia trachomatis. It is a common infection that can spread through anal, vaginal, and oral sex. It can also spread to an infant during childbirth.

Chlamydia does not usually cause any symptoms, but it can cause infertility and other complications if a person does not seek treatment.

If symptoms occur, they may include a change in vaginal discharge and burning pain during urination.e

Chlamydia can also affect the rectum if it occurs due to anal sex or spreads from another body area. This can lead to:

If symptoms occur, they will usually appear around 2 to 6 weeks after exposure.

Crabs, or pubic lice, usually attach to pubic hair. However, they can also affect the hair in the:

  • armpits
  • mustache
  • beard
  • eyelashes
  • eyebrows

They are very small and difficult to see, but a person may notice itching in affected areas.

After hatching, pubic lice look like tiny crabs. They can transmit during close physical contact, including sexual contact. They can also spread via shared towels or bed linen. However, they cannot spread via toilet seats.

To remove pubic lice in the genital area, a person can apply an over-the-counter medicated cream or shampoo from most drugstores and pharmacies. Speak with a pharmacist for advice on suitable products.

If pubic lice affect the hair near the eyes, a person may need a prescription medication.

The herpes simplex virus (HSV) is a common virus that can affect various parts of the body. It causes genital herpes.

HSV-1 usually affects the mouth. It can spread through saliva or if there is a sore around another person’s mouth. It can pass to the genital area during oral sex.

HSV-2 usually affects the genital area, the anal area, and the mouth. It transmits through vaginal, oral, and anal sex. Wearing a condom will not completely prevent transmission.

Both types of HSV can transmit from person to person when the skin has no visible sores.

HSV-1 and HSV-2 can both cause genital herpes.

Herpes cannot spread via utensils, toilet seats, swimming pools, soaps, or bedding. However, if a person touches a body part with herpes and then touches another part of their body, the herpes can spread to that area.

Once present, herpes stays in the body. However, it may remain dormant, and many people will never develop symptoms. Similarly, a person may have asymptomatic herpes and shed active virus without any symptoms.

The main symptoms are blisters around the mouth, anus, or genital area. These blisters can break, causing a painful sore that takes a week or longer to heal. Symptoms may also include pain when urinating and unusual discharge.

Some people never have symptoms, some have only an initial outbreak, and some have repeated outbreaks.

The first bout is usually the most severe, but people with weak immune systems have a higher risk of severe symptoms. Herpes can also increase the chance of contracting or transmitting HIV.

There is currently no cure, but medication can help relieve any symptoms. Daily or episodic antiviral medications can help prevent the spread of herpes.

Hepatitis B can cause a long-term infection and result in liver damage. Once a person has the virus, it can remain in their semen, blood, and other bodily fluids.

Transmission is possible through:

  • sexual contact
  • using nonsterile equipment for injections, tattoos, or piercing
  • unscreened or infected blood transfusions

This infection can pass to a baby during pregnancy or delivery. However, a doctor can advise on ways to prevent this. As long as the nipples have no cracks, the risk of transmitting the virus through breast milk is negligible.

Safe and effective hepatitis B vaccinations are available, and healthcare professionals recommend them for everyone.

If someone is unaware of their vaccination status and is at risk for hepatitis B, they should speak with a healthcare professional.

Trichomoniasis, or trich, can affect anyone, but it is more common in people assigned female at birth. Trichomonas vaginalis causes this infection.

In females, it is most likely to affect the vagina. In people assigned male at birth, the infection can develop in the urethra. Transmission can occur through penetrative sex and vulva-to-vulva contact.

Many people do not experience any symptoms. If symptoms do occur, they may include:

Trich can also lead to pregnancy complications and increase the chance of contracting and transmitting HIV.

A healthcare professional can prescribe medications to resolve trich, but both partners will likely need treatment, or the infection may return.

HIV is a virus that attacks the immune system. It can transmit through sexual contact and some other means.

HIV makes a person more prone to certain other infections. Without treatment, this susceptibility to opportunistic infection worsens and may lead to life threatening complications.

Once someone has HIV, the virus will be present in their bodily fluids, including semen, blood, breast milk, and vaginal and rectal fluids. If these fluids enter another person’s body, that person can also contract HIV.

This can happen through sexual contact, sharing needles, contact with broken skin, giving birth, and nursing.

Treatment can reduce the amount of the virus present in the body to an undetectable level. This means that the amount of the virus within the blood is so small that blood tests cannot detect it. It also means that it cannot spread to other people.

Someone with undetectable HIV must continue to follow their treatment plan exactly as the doctor prescribes to keep virus levels low.

Some other ways to reduce the risk of transmission include:

  • using a condom or other barrier method of contraception during vaginal or anal sex
  • taking preexposure prophylaxis, a drug that can help prevent HIV in people with exposure to the virus
  • not sharing needles
  • using gloves and disposing of sharps carefully, such as when working in a healthcare setting

In emergency situations, people can also take postexposure prophylaxis within 3 days of possible exposure to HIV.

Human papillomavirus (HPV) is a group of viruses that affect the skin and mucous membranes, such as the:

  • throat
  • cervix
  • anus
  • mouth

There are various types, and some pose a higher risk of cancer than others.

HPV is common. Many people experience no symptoms, but some types of HPV can cause genital warts.

Having HPV can also increase the risk of cervical cancer and throat cancer. This means that it is important to contact a doctor as soon as a person has concerns about HPV.

HPV can spread through:

  • vaginal and anal sex
  • oral sex
  • genital-to-genital contact

Vaccination, such as with the Gardasil 9 vaccine, can help prevent the transmission of HPV. Speak with a doctor for more information about vaccinations against HPV. It is generally best to receive the vaccination before any expososure to HPV, often from around the age of 11 years.

The doctor can also advise on HPV screenings. For example, they may recommend routine screening for people at high risk of cancer due to HPV, as well as regular screenings for cervical cancer in females.

Vaccines and screenings can help lower the risk of HPV and related cancer. Other preventive measures include:

  • using condoms or other barrier methods, though this will not fully protect against HPV
  • stop having sex as soon as the person notices genital warts
  • having sex with only one partner

Molluscum contagiosum is a viral skin infection that is usually benign. Some healthcare professionals do not consider it an STI because it can occur commonly without sexual contact.

It can affect adults and children. Among adults, transmission tends to occur through skin-to-skin contact or lesions, such as during sexual activity.

Symptoms include small, round bumps with indents on the skin. The bumps usually disappear without treatment, but this can take time, and it remains transmissible while the bumps are present.

Some ways of removing the bumps include:

  • applying certain prescription medications
  • applying chemicals or an electrical current
  • freezing them

Using a barrier method of contraception can help prevent the transmission of the virus. Anyone with the virus should wash their hands carefully after touching an affected area of skin to prevent the spread of the virus to another body part or person.

They should also avoid shaving in areas with visible lesions to prevent further spread.

Scabies is a skin condition that develops due to Sarcoptes scabiei, a mite. Like molluscum contagiosum, some healthcare professionals may not consider scabies an STI.

This condition can cause a very itchy, pimple-like rash to appear anywhere on the body. Symptoms may appear within 4 to 8 weeks of infection. However, people can transmit scabies before developing symptoms.

Transmission usually occurs through skin-to-skin contact and due to sharing items such as towels and bedding. In many cases, transmission is not through sexual contact.

A doctor can prescribe topical creams that kill the mites. When a person has scabies, they should avoid skin-to-skin contact with others. Once it clears up, they should decontaminate any personal items, including all bedding and clothes.

If someone has scabies, everyone in their household, partners, or any other close contacts will also need treatment to break the reinfestation cycle.

Syphilis stems from an infection with the bacterium Treponema pallidum. It is a potentially serious infection, and early treatment is necessary to prevent permanent damage and long-term complications.

There are usually four stages:

  • Primary: People may notice a painless sore or sores at the site of infection, such as around the genitals, anus, rectum, or mouth. The sores tend to last for 3 to 6 weeks, and people often do not notice them.
  • Secondary: People may have a rash on the hands and feet or other body parts. Other symptoms may include swollen lymph nodes, headaches, fatigue, and more.
  • Latent: Symptoms disappear, but the bacteria remain in the body and can continue to cause damage.
  • Tertiary: Life threatening complications can affect the brain, nervous system, eyes, and other organs. Symptoms at this stage will depend on which part of the body the syphilis affects.

The bacterium can spread at any point during the infection. Syphilis can also pass to a baby during pregnancy.

People can test to see if they have syphilis. If the result is positive, the person should inform their sexual partner or partners, and they should also seek medical advice.

Healthcare professionals will typically treat syphilis with antibiotics.

Gonorrhea is an infection that develops due to the bacterium Neisseria gonorrhoeae. Without treatment, it can lead to severe complications.

Gonorrhea can transmit during oral, vaginal, or anal sex. It can pass to an infant during childbirth. If a person touches an affected area of the body and then touches their eye, gonorrhea can also lead to pink eye.

Neisseria gonorrhoeae thrive in warm, moist parts of the body, such as the:

  • vagina
  • penis
  • mouth
  • rectum
  • eye

There are often no symptoms. If they do occur, they may vary depending on the potential body part. Symptoms may include:

In females, the infection can lead to pelvic inflammatory disease. Males may experience inflammation of the epididymis, which is the tube that stores sperm.

Both conditions can affect fertility.

Treatment with antibiotics can usually resolve the infection.

Chancroid is a bacterial infection that develops due to Haemophilus ducreyi. It can only spread through sexual contact. It is rare in the United States.

It causes painful sores on the genitals. Chancroid can also increase the chance of HIV.

Treatment is with antibiotics. Anyone who receives a diagnosis of chancroid should inform any partners they have had sexual contact with within the past 10 days.

Using a condom, dental dam, or other barrier method of contraception can help lower the risk of getting many STIs, though this will not prevent the transmission of infections that spread as a result of skin-to-skin contact.

Some other ways to reduce the risk of transmitting or contracting an STI include:

  • talking with new partners about protected sex and any past infections
  • ensuring that both partners undergo testing before starting a new sexual relationship
  • receiving vaccinations to protect against some infections
  • getting regular testing for STIs and seeking appropriate treatment if any are present
  • reducing the number of sexual partners

People should seek medical advice if they think that they have had exposure to an STI. Many STIs will not cause symptoms, so a person should not wait until symptoms appear before seeing a healthcare professional.

Home testing kits for various STIs are also available online, though a person should seek confirmation of the result from a doctor.

People may find it hard to talk about STIs due to concerns about stigma. However, STIs are a common health concern, and treatments are available that can either cure the infection or help a person manage it.

Seeking early treatment will also reduce the risk of complications.

A primary care doctor or a specialist clinic can help. For anonymous advice, a person can call the CDC-INFO national hotline (800-232-4636).

Examples of sexually transmitted infections (STIs) include chlamydia, public lice, hepatitis B, herpes simplex virus (HSV), trichomoniasis, HIV, molluscum contagiosum, scabies, human papillomavirus (HPV), syphilis, gonorrhea, and chancroid.

Many STIs do not cause symptoms. If symptoms occur, they may differ depending on the type of STI a person has.

People should speak with a healthcare professional if they think they may have an STI. Treatment will vary depending on the type of STI, but may involve antibiotics or topical creams.

Getting vaccinations may help prevent STIs. People can also reduce their risk by using barrier method contraception and speaking with new partners about STIs and testing before any sexual contact.