After two weeks of stable condition, he had a sudden recrudescence of the skin rash.

recrudescence 是由前缀 re-（表示"再次"）和拉丁词根 crudescere（意为"变粗糙、恶化"）组合而成。这个词在医学语境中特指"症状的突然复发或加重"，比普通用词"recurrence"（复发）更强调病情的急剧恶化特征。