SKIN1004 Hyalu-Cica Sun Serum vs Round Lab Birch Juice Sunscreen: Which Korean SPF Should You Buy?

Korean sunscreens have become the internet's go-to answer for "sunscreen that doesn't feel like sunscreen," and these two show up constantly in the same breath. SKIN1004's Hyalu-Cica Water-Fit Sun Serum built its following on a genuinely watery, serum-like texture aimed at oily and combination skin. Round Lab's Birch Juice Moisturizing UV LOCK took the opposite route — a glowy, cushiony lotion that went viral for its "glass skin" finish and sold out repeatedly at Olive Young in Korea. We did not run our own side-by-side skin test — this is a roundup of verified Amazon owner data plus independent editorial and professional reviews of each.

At a glance

A note on the table: the Round Lab listing sold on Amazon US is a reformulated version using FDA-approved filters (Avobenzone, Homosalate, Octisalate) rather than the Tinosorb M and Uvinul filters used in the original Korean formula sold at Olive Young — which is independently rated SPF 55 by the Korea Institute of Dermatological Sciences, per Dr Rachel Ho's review. One Amazon reviewer, Nalini Sahai, specifically flagged this: "Didn't realize this is the American version until it was too late... Less sheen than the original Korean version." Worth knowing before you buy either version.

SKIN1004 Hyalu-Cica Water-Fit Sun Serum: what reviewers and owners say

K Beauty Hobbit, an independent K-beauty blogger, tested this sunscreen through several days of heavy sun and heat exposure in Las Vegas, applying and reapplying it daily "including around my eyes, neck, ears, and arms," and reported no burning at all and no pilling "even with many reapplications." Her verdict was about as close to a rave as this genre gets: "there isn't a single bad thing I can say here, other than I need this to come in a giant pump bottle." NBC Select's dermatologist-sourced roundup of Korean sunscreens similarly singled it out as ideal "for oily, combination, or congestion-prone skin types," noting the "serum-watery texture absorbs so completely that there's genuinely nothing sitting on the surface."

Amazon's 1,890 ratings average 4.4 out of 5, with 30,000+ units bought in the past month alone. Amazon's own AI-generated summary of the reviews describes the sunscreen as effective, moisturizing without being oily, and lightweight, though it flags that "opinions about its non-greasy nature are mixed" and that some reviewers report eye stinging. One detailed reviewer, "Luffy's Mom I Real Life Tester," praised the fragrance-free formula and pump packaging but noted that on her oily skin, "I can still feel it on my face, and after about one to two hours, I notice some oiliness and shine." Another reviewer, Breezy, compared it favorably to a different sunscreen: "My eyes sting regardless of which sunscreen I use, but I feel like this isn't nearly as bad as the COSRX Vitamin E sunscreen I previously bought."

Round Lab Birch Juice Moisturizing UV LOCK: what reviewers and owners say

Dr Rachel Ho, an aesthetic doctor in Singapore who reviews sunscreens professionally, gave this one a measured take rather than a rave. She noted the original Korean formula's SPF and PA ratings were independently verified at SPF 55 / PA++++ by the Korea Institute of Dermatological Sciences, and praised its lightweight texture and lack of pilling or irritation in her testing. But she was direct about its limits: "Despite what its name suggests, Round Lab Birch Juice Moisturising Sunscreen does not feel moisturising at all," and users with normal-to-dry skin "will benefit from layering this sunscreen on top of their moisturisers." She also flagged that the Tinosorb M filter in the original formula "may cause a white cast on some users due to its white colour." Her overall verdict: "an affordable basic and functional sunscreen," best suited to oily or acne-prone skin. Organic Beauty Lover's Andrea Lee reached a similar conclusion after her own testing, calling it "a very light lotion with no white cast" but "not the lightest of lightest," and noting its ingredient list is more synthetic than Beauty of Joseon's comparable formula.

Amazon's owner reviews tell a notably more enthusiastic story. Its 2,688 ratings average 4.4 out of 5, and the top reviews read like genuine converts: "A Generational Leap Forward in Texture & Comfort" (L.F.), "I want to gatekeep this SO bad... hands down the BEST sunscreen I've ever used in my 32 years on Earth" (Clair.), and "The winning spf glow... your face has a shine like you wouldn't believe" (Darcy Deogny). One reviewer, Nalini Sahai, flagged that the Amazon listing is the US-reformulated SPF 45 version rather than the Korean SPF 50+ original. Another, Wesley Edwards, liked the dewy finish under makeup but noted "I could see my pores clogging a bit towards the end of the day" after wearing it with makeup all day.

Head-to-head: which should you buy

If you have oily, combination, or congestion-prone skin and want a sunscreen that genuinely disappears, the data leans toward SKIN1004: an independent reviewer who stress-tested it through days of sun and heat exposure came away with essentially no complaints, and NBC Select's dermatologist-sourced roundup specifically recommends it for that skin type. If what you're chasing is the glowy, dewy "glass skin" look, Round Lab's owner reviews are some of the most enthusiastic on Amazon — but the professional review is more measured, and dry-skin users should plan to layer a moisturizer underneath despite the "Moisturizing" name. The SPF nuance matters too: if you specifically want the SPF 50+/55 Korean-formula performance that made Round Lab viral, the US Amazon listing may not be exactly that product.

Before you buy: what to check

SKIN1004 also sells a separate mineral/physical sunscreen (the Air Fit Suncream) with different pros and cons — confirm the listing specifically says "Hyalu-Cica Water-Fit Sun Serum" if that watery texture is what you're after. Round Lab's own sun-care line includes several other formats (Mild-up UV Lock, Sun Serum, Sun Stick, Sun Cushion) with different price points and Amazon review volumes — confirm the listing says "Birch Juice Moisturizing UV LOCK" specifically, and check whether you're comfortable with a US-reformulated filter system versus the original Korean version. Both brands are sold directly by their official storefronts on the listings linked here (SKIN1004 NA and ROUNDLAB OFFICIAL), which reduces — though never fully eliminates — the counterfeit risk that affects popular K-beauty items on Amazon.

Sources

• Amazon customer reviews — SKIN1004 Hyalu-Cica Water-Fit Sun Serum, 1,890 verified ratings, 4.4/5 average
• Amazon customer reviews — Round Lab Birch Juice Moisturizing UV LOCK SPF 45, 2,688 verified ratings, 4.4/5 average
• K Beauty Hobbit — SKIN1004 Hyalu-CICA Water-fit Sun Serum review, independent K-beauty blog, 2022
• Dr Rachel Ho — Round Lab Birch Juice Moisturising Sunscreen review, aesthetic doctor, Singapore, 2023
• Organic Beauty Lover — My Honest Round Lab Sun Cream Review, 2023
• NBC Select — Best Korean Sunscreens, According to Dermatologists, 2026

Keeping this comparison current

Both brands adjust formulas, filters, and pricing periodically, and Amazon review counts and averages shift over time. We revisit comparisons like this rather than treating them as a one-time snapshot, and will update this page if either listing's formula, SPF rating, or availability changes materially.