Ulcers occur when the stomach's natural acids eat into the lining of the stomach.
胃酸腐蚀胃壁时，就出现了溃疡。
《柯林斯英汉双解大词典》
2
Some drugs can irritate the lining of the stomach.
有些药物会刺激胃内壁。
《牛津词典》
3
Recently physicians have determined that stomach ulcers are not caused by stress, alcohol, or rich foods, but a bacterium that dwells in the mucous lining of the stomach.