8 symptoms of the most common STDs explained

• There are millions of new sexually transmitted infection diagnoses every day.
• If left untreated, STIs can lead to infertility, pelvic inflammatory disease, and sight or hearing loss, among other chronic conditions.

As sexually transmitted infection (STI) cases continue to rise, knowing how they're spread and the symptoms can protect your health.

There are dozens of sexually transmitted infections, which primarily spread through sexual contact, according to the CDC. The four most common STIs are chlamydia, gonorrhea, syphilis and trichomoniasis, and there are an estimated 374 million new infections each year, according to WHO.

If left untreated, STIs can lead to conditions like infertility, hearing or sight loss, ectopic pregnancy, and pelvic inflammatory disease. Some STIs can also increase a person's risk of cervical, vulvar, vaginal, penile, or anal cancer.

To prevent STIs, use condoms during sex and have one sexual partner, if you can, the CDC website says. There are vaccines for HPV and hepatitis B.

And if you test positive for an STI, treatment options may include doctor-prescribed antibiotics or antiviral medications, or if the STI isn't curable, treatments for reducing symptoms. If you're sexually active with multiple partners, getting regular STI tests can also prevent their spread.

Here are eight common STIs, how they're transmitted, and their symptoms.