Onsen-Sui

Onsen-Sui is a mineral-enriched thermal water sourced from natural hot springs. It contains dissolved minerals and trace elements that accumulate as water passes through geological formations, giving it a distinct mineral composition compared to standard purified water.In skincare formulations, Onsen-Sui typically serves as a hydrating base ingredient. Its mineral content may help support the skin's natural barrier and maintain moisture levels, though the specific benefits depend on the mineral profile of the particular spring source.

The minerals present in thermal water are absorbed through the skin's outer layers. These minerals — which may include calcium, magnesium, silica, and others — can help reinforce the skin barrier by supporting its structural integrity and water-retention capacity.Additionally, the slightly alkaline pH of some thermal waters may have gentle soothing properties, though this varies depending on the mineral composition of the specific spring.

Onsen-Sui is typically used as a hydrating toner or essence applied to clean skin, either as a base layer before serums and moisturisers or as a standalone hydration step. Apply with a cotton pad or patting motion with fingertips. It can be used daily as part of your regular routine and layers well with other active ingredients.

Thermal water is generally well-tolerated across skin types. Those with very sensitive skin should perform a patch test first, as mineral content can occasionally trigger sensitivity in susceptible individuals.