Researchers studied Dutch swingers to find out about whether and why they used drugs.
Scientists were able to identify conditions using data from social media.
Donovanosis causes beefy, red blisters that bleed easily to appear on the genitals.
"It's yet another good reason to pack the condoms for the summer holidays—and actually use them," one doctor said.
If left untreated, syphilis can cause serious health conditions, including blindness and neurological disorders that can result in death.
The AHF called Tinder "a digital bathhouse for millennials" in a press release about the billboards.