The relation between the winter solstice and yuzu is not necessarily clear, but the practice of yuzuyu appeared after the birth of sento and according to one theory, it is related with the play on words linking "湯治, toji" (hot spring cure) and "冬至, toji" (winter solstice) and the idea that if the body is healthy, it is "yuzu-ga-kiku" (malleable, adaptable).
冬至と柚子との関連はかならずしも明らかでないが柚子湯の習慣は銭湯の登場以後のことであり、一説に湯治（とうじ）と冬至（とうじ）との語呂合わせで、身体息災であれば融通（ゆうずう）がきくとのこじつけであるという。