Is it normal for diarrhea to cause very intense burning and itching in the anal area?

It's common: Diarrhea tends to irritate the anus, especially in patients with hemorrhoids. Burning and itching are the most common symptoms of external hemorrhoids. Good perianal hygene via Sitz baths or long soaks in a regular bath tub are suggested to control your symptoms. Sometimes cortisone cream can help too. However, if you also have bleeding with diarrhea, consider an evaluation with a doctor.