Syphilis is on the rise in the U.S., but only among men.

The Center for Disease Control and Prevention reports syphilis infections increased by eleven-percent in 2012.

The CDC says the jump was primarily among men who identify as gay or bisexual. Syphilis is an STD that can be easily cured by antibiotics.

Its symptoms include small, painless sores or a rash.

The CDC estimates that 20 million new STD infections happen each year, with over half occurring in people between the ages of 15 and 24.

Gonorrhea infections increased by about four-percent in 2012, and rates of chlamydia remained the same.