What are the causes of an itchy anus?

Caffeine: Is the most common cause of anal itching not hemorrhoids as stated win the ads. Pinworms can be another cause usually in children after playing in the dirt. But cokes, coffe, tea, chocolate, and energy drinks like red bull have lots of caffeine leading to severe itching and bleeding, even waking you from your sleep at night clawing at your bottom. Stop the caffeine!