O Button (Blood Type) 🅾️

The O button emoji is a simple capital letter O displayed within a red or white circle, directly resembling the universal blood type label used in hospitals and medical settings worldwide. The circular border and clear typography make it unmistakable as a formal health or medical marker.

Beyond its literal medical application, the O button appears in casual conversation when people reference blood types—particularly in cultures where blood type personality theory (popular in Japan and East Asia) influences dating and friendship dynamics. Some users playfully drop it to indicate their blood type in bios or conversations, treating it as a personal identifier. It's also occasionally used generically as a circled O in word games or alphabetic sequences.

The emoji's design remains consistent and recognizable across platforms, though its usage remains relatively niche outside of medical or culturally specific contexts. In Western digital culture, it's far less common than in regions where blood type categorization holds social significance.

Approved in 2010 as part of Unicode Emoji 0.6, the O button has maintained its primary identity as a blood type marker, though it occasionally crosses into informal personal expression in communities where blood typing carries cultural meaning.