Causes of Duodenal Ulcer
A duodenal ulcer arises when the protective mechanisms that protect the epithelial lining are compromised. The incoming acidic chyme from the stomach can erode the lining of the duodenum. The most common causes of duodenal ulcers, like stomach ulcers, include H.pylori infection and the use of NSAIDs.

1. Helicobacter pylori (H.pylori) Infection
-- H.pylori is a type of bacteria that infects the stomach lining but may also extend to the duodenum especially if the duodenal mucosa is altered in a manner that it resembles the stomach lining (gastric metaplasia).
-- H.pylori increases gastric acid secretion in the stomach and also degrades the mucus barrier.
-- This allows gastric acid to make contact with the duodenal lining, leading to inflammation and eventually ulceration.

2. Non-steroidal anti-inflammatory drugs (NSAIDs)
-- NSAIDs are widely available drugs used to reduce inflammation and ease pain.
-- These drugs impair the mucus barrier of the duodenum thereby allowing gastric acid to make contact with the duodenal lining.
-- Chronic use of NSAIDs are more likely to lead duodenal ulceration.