Sexually transmitted diseases are infections spread mainly by contact with genitals or bodily fluids. Also called STDs, STIs or venereal disease, sexually transmitted infections are caused by bacteria, viruses or parasites.

Sexual activity includes genital touching or sexual intercourse. Anyone who is sexually active can get an STI. You can lower the risk of an STI, and one of the best ways is to talk about STIs with a new partner before sexual activity.

Some STIs cause no symptoms or only mild symptoms. But even with no symptoms, STIs can spread to others. Testing is the only way to be sure if you have an STI.

Some STIs are easy to treat and cure. Others are more complicated. Treatment is important so you don't spread the disease. Treatment also can help prevent fertility trouble, organ damage or some cancers.

Chlamydia is an infection of the genital tract. Germs called bacteria cause it. Early on, chlamydia infections often cause few or no symptoms. If you get symptoms, they usually start 5 to 14 days after you've been exposed to chlamydia germs. The symptoms may be mild.

Signs and symptoms may include:

• Painful urination, which may feel like burning.
• Pain in the lower part of the stomach area, also called the abdomen.
• Lower back pain.
• Fever.
• Vaginal discharge.
• Discharge from the penis.
• Vaginal pain during sex.
• Bleeding between periods.
• Testicle pain or swelling.
• Rectal pain, discharge or bleeding.

Gonorrhea is an infection of the genital tract. Germs called bacteria cause it. Symptoms of infection in the female genital tract tend to appear within 10 days of exposure to the germs. Symptoms of infection in the male genital tract often start within five days after exposure.

Gonorrhea symptoms can include:

• Thick, cloudy or bloody discharge from the penis or vagina.
• Pain or burning sensation when urinating.
• Heavy menstrual bleeding or bleeding between periods.
• Painful, swollen testicles.
• Painful bowel movements.
• Pain in the pelvis or stomach area.
• Anal itching.
• Rectal discharge, soreness or bleeding.
• Painful bowel movements.

Gonorrhea germs also can grow in the mouth, throat, eyes and joints such as the knee. Gonorrhea symptoms in body parts beyond the genitals can include:

• Eye pain, itching, sensitivity to light and discharge.
• Throat soreness or swollen glands in the neck.
• Joint warmth, swelling or pain when moving.

Trichomoniasis is a common sexually transmitted infection caused by a parasite that is too tiny to see with the eyes. The parasite is called Trichomonas vaginalis. This organism spreads during sex with someone who already has the infection. It often infects the vagina, vulva or cervix. It also tends to infect the tube through which urine leaves the penis or vagina, called the urethra.

When trichomoniasis causes symptoms, they may appear within 5 to 28 days after being exposed to the parasite. The symptoms range from mild irritation to serious swelling called inflammation.

Trichomoniasis symptoms can include:

• Clear, white, greenish or yellowish vaginal discharge.
• Discharge from the penis.
• Strong vaginal odor that may smell fishy.
• Vaginal itching, burning, soreness or irritation.
• Itching or irritation inside the penis.
• Pain during sex.
• Painful urination.
• Rarely, pain in the lower stomach area.

HIV is an infection with the human immunodeficiency virus. HIV interferes with the body's ability to fight off viruses, bacteria and fungi that cause illness. Without treatment, it also can lead to AIDS, a chronic, life-threatening disease.

The symptoms of HIV vary by how long you've had the disease and whether you get treatment for it.

Most often, HIV causes flu-like symptoms about 2 to 4 weeks after being infected. These symptoms may last for a few days or for weeks. During this time, the virus makes copies of itself fast. The risk of passing the disease to sexual partners is high.

Early HIV symptoms can include:

• Fever.
• Chills.
• Headache or muscle aches.
• Sore throat.
• Swollen lymph glands.
• Rash.
• Fatigue.
• Night sweats.
• Mouth ulcers.

The only way you know if you have HIV is to be tested.

Over time, the HIV virus keeps making copies of itself, but at lower levels. This is called the chronic stage of infection. You might not have any symptoms during this time. If you take HIV medicines called antiretroviral therapy exactly as prescribed, you might stay in this stage for life.

• Swollen lymph nodes, which are often one of the first signs of HIV infection.
• Diarrhea.
• Weight loss.
• Fever.
• Cough and shortness of breath.

Without HIV treatment, the chronic stage of HIV infection may progress to AIDS in about 10 years. AIDS is life-threatening. Symptoms of AIDS can include:

• Fever.
• Weakness.
• Fast weight loss.
• Extreme tiredness.
• Soaking night sweats.
• Fever that keeps coming back.
• Ongoing swelling of lymph nodes in the armpits, groin and neck.
• Diarrhea that lasts longer than a week.
• Sores in the mouth, anus or on the genitals. Discolored blotches on or under the skin, or inside the eyelids, nose or mouth.
• Memory loss.
• Depression.
• Infections such as pneumonia.

Genital herpes is a sexually transmitted infection that spreads easily. It's caused by a type of the herpes simplex virus (HSV). The virus enters the body through small breaks in the skin or mucous membranes. Most people with HSV never know they have it. That's because they have no symptoms or symptoms are too mild to be noticed. If there are symptoms, they tend to appear within 12 days of being exposed to HSV.

If you notice herpes symptoms, the first time you get them tends to be the worst. Some people never get symptoms again. For others the symptoms come and go over many years.

Genital herpes symptoms can include:

• Small red bumps, blisters called vesicles or open sores called ulcers. These symptoms often show up around the genitals, rectum and mouth. They may take a week or longer to heal.
• Pain or itching around the genital area, buttocks and inner thighs.
• A feeling of pressure in the stomach area.
• Vaginal discharge.

Ulcers can make urination painful. People may have pain and tenderness in the genital area until the infection clears. During a first bout of symptoms, you may have flu-like symptoms as well. Those symptoms can include a headache, muscle aches and fever, as well as swollen lymph nodes in the groin.

Sometimes, the infection can be spread even when sores aren't present.

HPV infection is one of the most common types of sexually transmitted infections. Some forms of HPV greatly raise the risk of cervical cancer. Other forms cause genital warts. Most often, HPV has no symptoms.

Symptoms of genital warts include:

• A small bump or group of bumps in the genital area. These can be large or small, and raised or flat.
• Several warts close together that take on a cauliflower shape.
• Itching or discomfort in the genital area.
• Bleeding with sex.

Rarely, warts can also grow in the mouth or throat of a person who has had oral sex with an infected person.

Hepatitis A, hepatitis B and hepatitis C are all contagious infections that affect the liver. They each are caused by a different virus. Hepatitis B and C are more serious than hepatitis A. But each can inflame the liver.

Some people never get hepatitis symptoms. For those who do, the symptoms may happen weeks after exposure to one of the hepatitis viruses.

Hepatitis symptoms can include:

• Fatigue.
• Upset stomach and vomiting.
• Pain or discomfort in the stomach area, especially in the area of the liver on the right side beneath the lower ribs.
• Loss of appetite.
• Fever.
• Dark urine.
• Stool that's the color of clay.
• Muscle or joint pain.
• Itching.
• Yellowing of your skin and the whites of your eyes, also called jaundice. Yellowing may be harder to notice on brown or Black skin.

Syphilis is an infection caused by germs called bacteria. The disease affects the genitals, skin, mouth and anus. It also can involve many other parts of the body, including the brain and heart.

The symptoms of syphilis may happen in three stages — primary, secondary and tertiary. Some people also have syphilis without symptoms, but syphilis germs are still found in the blood. This is called latent or inactive syphilis.

During the first stage of syphilis, one or more small, painless sores called chancres form where the germs entered the body. Usually they form in the genitals, rectum, tongue or lips. Often, a chancre is painless, firm and round.

As syphilis becomes worse, the symptoms can include:

• Rash marked by rough discolored spots over any area of the body, including the palms and soles. The rash often doesn't itch.
• Fever.
• Swollen lymph nodes.
• Fatigue and a vague feeling of discomfort.
• Headaches or muscle aches.
• Loss of patches of hair.
• Weight loss.
• Sore throat.

Without treatment, syphilis bacteria can spread. This can lead to serious internal organ damage and death years after the original infection.

Some of the symptoms of late-stage syphilis include:

• Lack of coordination or loss of feeling from nerve damage.
• Paralysis.
• Blindness.
• Dementia.
• Deafness.

If a pregnant person with syphilis passes the germs to the unborn infant, it's called congenital syphilis. This condition can be disabling or even life-threatening. So, it's important for pregnant people with syphilis to be treated.

At any stage, syphilis can spread and affect:

• The brain and spinal cord, also called neurosyphilis.
• The eyes, called ocular syphilis.
• The ears, called otosyphilis.

Neurosyphilis symptoms can include:

• Serious headaches.
• Muscle weakness and trouble with muscle movements.
• Confusion, trouble focusing or behavior changes.

Neurosyphilis also is linked with a group of symptoms called dementia that affect memory, thinking and social skills.

Ocular syphilis symptoms can include eye pain and changes in vision, including blindness.

Otosyphilis symptoms can include:

• Hearing loss.
• Ringing, buzzing or hissing in the ears, also called tinnitus.
• Dizziness.
• Feeling like you or the room around you is spinning.

You can help prevent sexually transmitted infections (STIs). Steps that lower the risk of getting or spreading STIs are to:

• Get key vaccines. Vaccines can help prevent hepatitis B and human papillomavirus infections passed through sexual activity.
• Limit your number of sexual partners. You can lower your risk of STIs by having sex with just one partner who only has sex with you.
• Get tested for STIs. Both you and your partner should get tested by your healthcare professionals before you have sex for the first time. Talk with each other about your test results.
• Use medicine to help prevent HIV if needed. If you might be at risk of HIV, talk with your healthcare professional. You may be prescribed medicine called pre-exposure prophylaxis (PrEP), which lowers your risk.
• Use condoms. Make sure that you or your partner puts on a new condom every time you have sex.
• Don't drink too much alcohol or use street drugs. Having lots of alcohol or using illegal drugs can cloud judgment. Both raise the chances of risky sexual behavior that could lead to an STI.
• Consider not having sex. This is the surest way to prevent STIs. The choice not to have sex is called abstinence.

See your healthcare professional if you think you might have a sexually transmitted infection or if you may have been exposed to one. Timely testing and treatment are needed to prevent or delay health problems that could be serious or life-threatening. Treatment also may be needed to prevent infecting others.