Why We Love It : “An essence is super helpful at kick-starting hydration in the skin,” notes Yoon, citing this step as integral to any K-beauty routine, best applied post-cleanser and toner. One CosRx’s most popular offerings, the lightweight essence is powered by 96.3% snail mucin—the buzzy K-beauty ingredient made popular for its resurfacing and hydrating properties—to fade dark spots, improve hydration, calm inflammation, and smooth skin texture—leaving skin soft and dewy. One CosRx’s most popular offerings, the lightweight essence is powered by 96.3% snail mucin—the buzzy K-beauty ingredient made popular for its resurfacing and hydrating properties—to fade dark spots, improve hydration, calm inflammation, and smooth skin texture—leaving skin soft and dewy.