The
三伏 (chūfú
初伏, zhōngfú
中伏, mòfú
末伏) are calculated from
庚 (gēng) days in the lunisolar calendar, starting on the third gēng day after summer solstice. Traditional medicine prescribes
三伏贴 (sānfútiē) — herbal patches applied during this hottest stretch to treat winter ailments.