Moisture from sweat or diarrhea may cause itching. If the anal skin
stays wet, the skin
begins to break down.
Some foods irritate the anus when they are expelled during a bowel movement. The most common culprits are caffeine, chocolate, beer, nuts, dairy products, and spicy food.
Infections such as pinworms, yeast, and genital warts can cause itching.
Hemorrhoids, which cause painful swelling of blood vessels in the anal area, can cause itching.
Cancer, in rare instances, may be a cause.