Hello! Thank you for the query. Anal burning has nothing to do with acid (I assume you have been thinking about stomach acid). There is no acid in the stool. Burning and pain while passing the stool are present because fissure is a kind of wound. This wound gets irritated with every stool, especially hard one. Chronic fissure is very hard to treat without the surgery. Please try such treatment: - increase fiber rich products and mineral water intake to avoid constipation - use stool softener if necessary - have sitz baths with Quercus Cortex twice a day - wash your anus after every stool - do not push hard on stool - use Nitroglycerine gel twice a day Such treatment should help in a week or so. If not, you should consult general surgeon. Hope this will help. Regards.