Stomach ulcers occur when a sore develop in the stomach or small intestine. They happen when the protective mucus lining the stomach failed to work.
In the stomach, there's presence of acid which help digest the intake food and also protect against microbes. In order to protect the tissue of the body from this acid, the stomach secrete a thick protective layer which prevent the tissue of the stomach from being attached by acid.. Ulcer occur when this protective layer worn away and stop functioning .This will give a way for the acid to attach the stomach

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Cause

Ulcer is usually cause due to excessive and prolong taking of Non - Steroidal Anti-inflammatory Drug(NSAID). Example of (NSAIDs) are Aspirin, Ibuprofen, Naprozen and so on. They are pain relieval drug .

Ulcer is also cause by bacteria Infection.

Hidden treatment.

Urea is a powerful tool to treat early Ulcer permanently. Many people are unaware of this . It has been tested and it works effectively. What you need to do is to collect your early morning urine and take small out of it. It may look irritating but if you are strong enough to take it, Ur ulcer is gone.

Reference
https://www.rdasia.com/healthsmart/10-signs-of-an-ulcer-you-should-never-ignore