医生建议他避免辛辣食物，以免加重口腔溃疡。

The doctor advised him to avoid spicy foods to prevent worsening his mouth ulcers.

ulcers 是 ulcer 的复数形式，ulcer 指"溃疡"，即皮肤或黏膜表面因组织坏死而形成的开放性伤口。在口腔中出现的溃疡俗称"口腔溃疡"。