Fungal infection of the genitals. "Cottage cheese" for the girls, "genital dandruff" for the boys. Other symptoms may include itching burning rashes bad smells or white discharge, but may also be largely asymptomatic.
Sexually transmittable, but not an STD per se, as one needn't have sexual contact to get it. JUST CAUSE YOU GET IT DOESN'T MEAN YOU FUCKED SOMEONE WHO HAD IT (OR ANYONE AT ALL, PERHAPS EVER), BUT IF YOU DO FUCK SOMEONE WHO HAS IT, YOU MAY GET IT. Can also be caused by dietary imbalances, bad personal hygiene, genetics, etc. etc.
Sometimes goes away on its own, sometimes damn hard to eliminate entirely despite throwing a whole pharmacy aisle of OTCs and a half dozen prescriptions at it.
Eating sugar will make it worse almost instantaneously if you have it.
Ooooh fuuuuuuuck it burns it burns oh please god kill me. This yeast infection shit's worse than hemorrhoids!