Some sexually transmitted diseases (STIs) can cause serious health problems. These infections can lead to infertility, organ damage, certain types of cancer and death if left untreated.

Most STDs spread during vaginal, oral or anal sex. Some can also spread through skin-to-skin contact or sharing needles or syringes.

1. Painful Urination

Painful urination (dysuria) is a common symptom of urinary tract infections (UTIs). UTIs are caused by bacteria that enter the urethra, which is the tube that carries urine from your kidneys to your bladder.

Females are more likely to develop UTIs than males because their urethras are shorter, which makes it easier for bacteria to get into the bladder.

Women also have a greater risk of getting UTIs when they are pregnant or menopausal. They may need to take antibiotics to treat their UTIs.

Doctors use a patient’s medical history, physical exam and lab tests to determine what is causing painful urination. They ask questions about how often the pain happens and whether it hurts when you begin urinating or at the end of your urination.

2. Bumps or Sores

Bumps or sores in the genital area, anus, or mouth may be a sign of an STD. They can be caused by genital herpes, syphilis, and chancroid.

They may be itchy, red, or swollen. They may also ooze or drain clear fluid.

You can get syphilis from direct contact with an infected person, such as during sex or by sharing personal items like utensils or towels.

The infection starts with small, red, fluid-filled blisters that form on the lips, tongue, gums, or on the back of your throat. These sores can go away and you’ll develop antibodies that prevent further infections. But if left untreated, they can spread to other parts of your body and cause more serious health problems.

3. Bleeding

Bleeding can be a sign of several health problems, including an STI or blood disorder. It’s important to talk to your doctor about it.

STIs can be transmitted from person to person by contact with infected fluids, such as from sexual intercourse or genital touching. They can also spread from a person’s body to another through the use of infected needles or drug paraphernalia.

Chlamydia is a bacterial infection of the genital tract that can cause pain, discharge and bleeding. It’s also a common infection of the rectum–the last portion of your large intestine before the anus–and is mainly caused by anal sex, says Jennifer Svets, MD, an assistant professor in gynecology at the University of Miami Medical School.

Symptoms may be so mild that you’re not aware of them or they may come and go over time, according to the Centers for Disease Control and Prevention. It’s important to get tested and treated early, especially if you have many sexual partners or have had unprotected sex.

4. Vaginal Odor

While vaginal odor isn’t always a sign of an STD, it can be one. A strong odor that’s accompanied by other symptoms (like burning, itching, discharge, or irritation) may be a warning that you have an infection.

It’s normal for your vaginal odor to change during certain times of the menstrual cycle, pregnancy or menopause, and right after you have sex. But if your odor gets too intense or persists, it’s a good idea to see a gyno.

A fishy odor can be the sign of bacterial vaginosis, which is caused by an imbalance in bacteria in your vagina. The infection is treated with an antibiotic. Other STIs that can cause a fishy odor include trichomoniasis and pelvic inflammatory disease.

5. Changes in Your Period

The menstrual cycle is an ongoing series of hormone-triggered phases that are a part of your life for as long as you live. Some slight variations to your menstrual cycle are normal and do not cause any concerns, but it is helpful to note any changes in your periods or symptoms you may be experiencing.

For instance, you should seek medical attention if your period becomes longer than usual or if it seems unusually heavy or painful. Your provider might perform a pelvic exam and order blood tests to determine the cause of your symptoms.

You should also consider getting a test for STDs, which are infections that are passed through sexual contact. They include chlamydia, gonorrhea and syphilis. These infections are common and easy to get tested for and treat.