ROUND LAB: Deep-Sea Minerals, Birch Sap, and Skincare That Trusts Its Ingredients

Dokdo is a cluster of volcanic islands in the East Sea, between Korea and Japan. Remote, windswept, and surrounded by some of the most mineral-rich deep-sea water in the region — it's also the source ingredient that defines ROUND LAB. The brand takes the water from around Dokdo, uses it as the primary base for its formulations, and builds products that are, almost conspicuously, about letting the ingredients do the work rather than impressing you with the formula.

Why mineral water in skincare is worth taking seriously

Skincare formulas are largely water. Most brands use purified water as their base — effectively a blank slate. ROUND LAB uses Dokdo deep-sea water, which carries a distinct mineral profile: magnesium, calcium, potassium, zinc, and trace elements accumulated at depth over long periods. These aren't decorative additions. Magnesium plays a role in skin barrier function and has documented anti-inflammatory properties. Calcium supports the natural desquamation (skin shedding) cycle, contributing to smoother texture over time. Zinc is antimicrobial and sebum-regulating.

The argument for mineral-rich water as a base ingredient is that it delivers these micronutrients continuously throughout the day via the products you're already using, rather than requiring additional steps. Whether this translates to dramatically different outcomes compared to purified water formulas is the subject of ongoing dermatological research — but the evidence for individual mineral benefits to skin is solid enough that ROUND LAB's positioning is scientifically coherent rather than merely poetic.

The Birch line and why it resonates

ROUND LAB's Birch series is the brand's bestselling range — toner, moisturiser, and serum built around birch sap, which is extracted from birch trees in early spring when it's running high with nutrients. Birch sap contains 11 amino acids, sugars, and minerals including manganese, zinc, and potassium. It has a composition that is unusually compatible with human skin — close enough to the natural moisturising factor (NMF) that it penetrates effectively and binds moisture at a structural level rather than just on the surface.

The Birch Juice Hydro Cream, used as either a moisturiser or an overnight mask, has become one of ROUND LAB's signature products: a texture that reads as lightweight but delivers significant hydration because of how the birch sap interacts with the skin rather than sitting on top of it. It layers well under SPF without pilling, which solves one of the most common frustrations in K-beauty routines.

Who ROUND LAB is genuinely for

ROUND LAB works particularly well for three groups: people with sensitive or reactive skin who need formulas that deliver results without triggering responses; people coming to K-beauty from conventional Western skincare who want a clean, straightforward entry point without needing to understand a complex system; and people who've been using actives (acids, retinol, vitamin C) and need a hydration-focussed, calming layer to support the skin around those treatments.

The brand's ingredient lists are notably short by K-beauty standards — ROUND LAB subscribes to the same minimalist philosophy as COSRX, though through a different lens. Where COSRX focuses on targeted actives, ROUND LAB focuses on foundational skin health: hydration, barrier support, mineral nutrition. The two approaches complement each other well, which is why ROUND LAB often appears alongside COSRX or ANUA in people's routines rather than competing directly with them.

Written by Nora — Team Koolseoul, Seoul.