I had gastritis (duodenitis, in fact) a couple of years back, and the first thing they did was test me for H. pylori. I didn't have it. Doctor told me a vast majority of people with such issues do.
After a gastroscopy, they concluded that it was just stress and nothing else, but inflamation wouldn't heal on its own, so I got pantoprazole (PPI) and stopped ingesting potentially irritating food (caffeine, alcohol, spicy food). I also shortly changed jobs, which alleviated the stress. Mind you, I never had heartburn, just pain. My condition didn't improve for a while after that, until I stopped drinking carbonated water (the only carbonated beverage I consumed), that fixed it in less than a month. After that, I gradually weaned myself off of pantoprazol in 6 months.
There literally was no other probable cause except for stress (I was stressed, wholly self-induced), and after I switched industries and no longer felt that I'm wasting my time working for peanuts, the PPIs helped cure the symptoms.
A perhaps easier to understand explanation of this is this part of a Robert Sapolsky talk on stress, prepositioned to the bit where he talks about the interaction of stress with the bacteria [1]. The summary is that the body is good at repairing the damage the bacteria do, unless the person is under constant stress which inhibits the repair work.
What is a bit of a myth? Sounds like stress is a factor but the bacteria is a direct cause in 90 percent of cases. The myth was that stress is "the cause".
50% of people are infected with H.Pylori, so clearly the bacteria isn't a cause on its own. The myth is more that "stress doesn't cause ulcers", which many people now believe.
Burns and other life threatening conditions are the main cause. Between 60 and 100% of patients entering the ICU have stress ulcers. Chronic workplace stress, job frustration and family problems are also associated with ulcer development.
