Smoking and aging are major risk factors for duodenal ulcers. Smoking decreases the secretion of bicarbonate from the pancreas and increases the secretion of hydrochloric acid and pepsin into the stomach and duodenum. This increases the concentration and activity of acid and pepsin in the digestive tract. The duodenal mucosa cannot withstand the digestive action of hydrochloric acid and pepsin, damaging the mucosa and preventing it from secreting enough mucus to act as a protective barrier against hydrochloric acid. This decreases the resistance of the mucosa and destroys blood vessels, leading to further erosion of the mucosa and pain and bleeding in the abdomen.