Reflux esophagitis can be classified into four grades based on the extent of esophageal mucosal damage: Grade A, B, C, and D. Grade A mainly involves damage to the folds of the esophageal mucosa, generally not exceeding 5 millimeters. Grade B refers to damage greater than 5 millimeters. Grade C indicates that the damage to the esophageal mucosa reaches 75% of the entire circumference of the esophagus; any damage below 75% falls into Grade C. Grade D, on the other hand, is quite severe, with extensive damage around the entire circumference of the esophagus, mainly divided into these four grades.