Sunscreen science
Most sunscreen questions come down to three things: which UV filters a formula uses, how much of it reaches your skin and how it behaves under makeup. In the US, sunscreens are regulated as over-the-counter drugs under an FDA monograph; in Korea, as functional cosmetics. These guides explain what that means for the bottle in your hand.
Korean or US Round Lab Birch sunscreen?
The Korean SPF 50+ PA++++ tube and the US SPF 45 version use different UV filters. Our comparison decodes both formulas, the FDA rules and the price per ml.
Read the evidence: Round Lab Birch Sunscreen: Korean SPF 50+ vs US SPF 45 →Why aren't Korean sunscreens FDA approved?
US law classifies sunscreen as an OTC drug limited to Monograph M020 filters; we explain the 2026 bemotrizinol order, PA versus broad spectrum, and import realities.
Read the evidence: Why Aren't Korean Sunscreens FDA Approved? →Why does my sunscreen pill after moisturizer?
Pilling is a film failure driven by unset or clashing layers, film formers and rubbing; our cause-to-fix table shows what to change without cutting the sunscreen dose.
Read the evidence: Why Does My Sunscreen Pill? Causes and Fixes →How much sunscreen does your face need?
About 1/4 teaspoon (1.1 g) for the face and 2/5 teaspoon with the neck matches the 2 mg/cm² SPF test dose; see the calculation and two-finger rule check.
Read the evidence: How Much Sunscreen Should You Put on Your Face? →Is SPF 30 or SPF 50 better for your face?
SPF 30 blocks about 96.7% of UVB and SPF 50 about 98%, so SPF 50 lets 40% less through. Our SPF 30 vs 50 guide shows when the higher number is worth it and why application amount matters more.
Read the evidence: SPF 30 vs 50 for Face: Which One Do You Need? →Do you need sunscreen in the winter?
From UV index 3, on fresh snow (over 80% reflected), at altitude and on long drives, yes. Our winter sunscreen guide has a situation-by-situation decision table, including cars and indoor windows.
Read the evidence: Do You Need Sunscreen in the Winter? When It Matters →
