Acidity is a very vague term used by many people when they have burning pain in the upper part of the stomach or behind the chest bone, burping and indigestion after meals. It can occur at any time and there may be no pathology or it can be related to stomach ulcer. Acid is produced by the glands in the stomach and some foods produce more secretion of acid than others. Pain in the chest can be related to acidity but not in the shoulders.