Anal itching is due to irritation of the skin around the anus accompanied by a desire to scratch. The intensity of itching increases with moisture, pressure, and sitting. At its most intense, anal itching causes intolerable discomfort described as burning and soreness. Scratching only makes the discomfort worse. Treatment of anal itching is to shower gently without directly rubbing or irritating the skin and to clean and pat dry the anus thoroughly. Use of moist pads rather than toilet paper after bowel movements can be helpful. Local application of cortisone cream may also reduce inflammation and itching, though prolonged use of cortisone may be damaging to the skin. If anal itching is prolonged, a physician should be consulted and a search made for the cause. Causes of anal itching include, but are not limited to, insufficient cleaning, ingesting spicy foods, diarrhea, anal tear, fungal infection, hemorrhoids, pinworms, anal abrasion, anal leakage, incontinence, and weeping.
Source: http://www.medicinenet.com