怎么了 is an interjection used to ask 'What happened?' or 'What's wrong?'—typically with concern, surprise, or empathy. It combines 怎 (how), 么 (a particle that forms interrogatives with words like 怎, 什, or 为), and 了 (a sentence-final particle indicating a change of state). Together, they express that something unexpected or troubling has occurred, prompting the speaker to seek clarification or offer help.

This phrase is informal and conversational, commonly used in spoken Chinese among friends, family, or colleagues. It often follows a visible cue—like someone looking upset, crying, or acting unusually—or appears after silence or hesitation. While it literally asks 'How did it become?', its pragmatic function is to signal care and invite explanation, not to request a literal description of 'how' something changed.