What causes an itchy anal cleft?

Yeast: Any area were skin meets skin tends to become moist. This can allow for our own natural surface bacteria and yeast to grow. Yeast often tend to overgrow and cause itching. I recommend keeping the area dry with powder like zeasorb (over the counter) which keeps yeast counts down.

Most commonly: This is due to excessive moisture and or caffeine. Eliminate all sources of caffeine, use corn starch powder liberally on the affected are as often as necessary to control symptoms and keep the area dry. Do not scrub with soap, use just plain warm water and do not rub. Wear loose fitting cotton underwear, no nylon or thongs.