To ulcerate is for a place on the body to break open and become an ulcer — a raw, open sore that does not heal in the normal quick way. It is used about skin (a leg that has been swollen for years may ulcerate) and about the inside of the body (the lining of the stomach can ulcerate). The word does not mean 'to hurt' or 'to get infected'; it means the tissue actually breaks down and stays open. This is a medical word. Doctors, nurses and medical writing use it; ordinary people almost never say it in conversation — they say 'it turned into an ulcer' or 'it opened up'. You will meet it most often as the participle 'ulcerated' (an ulcerated leg) or the noun 'ulceration'. It is usually intransitive: the wound ulcerates, the tissue ulcerates. Occasionally, in formal medical writing, you see it used the other way — a drug or a disease ulcerates the lining — meaning it causes the ulcer. Very rarely, older or literary writing stretches it to feelings: a grief that ulcerates, meaning something that sits inside and slowly eats away. Students will almost never need that use, but if you meet it in a novel, that is what is happening.

潰瘍、變成潰瘍（動詞）。台灣醫療上多說「潰瘍」「形成潰瘍」，例如「傷口潰瘍了」。注意中文的「潰瘍」既是名詞也常當動詞用，英文則要分 ulcer（名詞）和 ulcerate（動詞）。