A mouth ulcer or stomatitis: an inflammatory sore or erosion on the mucous membrane of the mouth, often painful and sensitive to food.
ストレスで口内炎ができて、食事がつらい。
I got a mouth ulcer from stress, and eating is painful.
口内炎の治療には軟膏やうがい薬が使われることが多い。
Ointments and mouthwashes are often used to treat mouth ulcers.
口内炎がひどいと固いものや酸っぱい物がしみる。
Severe mouth ulcers make hard or sour foods sting.