This guide explains what "SPF 50+" and "PA++++" on a sunscreen label really mean, and which grade to use and how to apply it in daily life. It draws on Korea's Ministry of Food and Drug Safety (MFDS) regulations on functional cosmetics and its standards for measuring UV protection.
The two kinds of UV light: UVA and UVB
The ultraviolet light that reaches the ground splits into two types by wavelength.
- UVB (290 to 320 nm) acts on the upper skin and causes sunburn and skin cancer. Its intensity swings a lot with the time of day and the season.
- UVA (320 to 400 nm) reaches the deeper skin and drives photoaging and skin cancer. Photoaging shows up as wrinkles, dark spots and loss of firmness. UVA stays fairly steady all year and passes through window glass.
The key point. SPF reflects UVB protection and PA reflects UVA protection. You need to check both ratings for full coverage against UV light.
SPF, the UVB protection factor
Definition
SPF (Sun Protection Factor) is the minimal erythema dose (MED) with sunscreen applied, divided by the MED with no sunscreen. It is measured under the MFDS standards for UV protection (in vivo, ISO 24444).
SPF 30, for example, means it takes 30 times as long for skin to redden when the product is on.
SPF protection rate
| SPF grade | Theoretical UVB block | 1/SPF |
|---|---|---|
| SPF 15 | about 93.3% | 1/15 passes through |
| SPF 30 | about 96.7% | 1/30 passes through |
| SPF 50 | about 98.0% | 1/50 passes through |
| SPF 100 | about 99.0% | 1/100 passes through |
The gap between SPF 50 and SPF 30 is only about 1.3 percentage points, which is small. Still, people often apply less than the recommended amount, so a higher SPF gives you a margin of safety.
Korea's labeling rules
Under MFDS notice, SPF 50+ is the highest grade you can print in Korea. Anything that measures 50 or above is all labeled "SPF 50+". The U.S. FDA and Japan's health ministry cap the label at 50+ as well.
PA, the UVA protection grade
Definition
PA (Protection grade of UVA) started in Japan and is used in Korea and parts of Asia as a UVA protection grade. It is based on a PPD (Persistent Pigment Darkening) measurement, the lasting tan that UVA causes.
PA grades
| PA grade | PPD value | UVA protection |
|---|---|---|
| PA+ | 2 or more, under 4 | Low |
| PA++ | 4 or more, under 8 | Moderate |
| PA+++ | 8 or more, under 16 | High |
| PA++++ | 16 or more | Very high |
Europe uses a UVA seal instead of PA, the letters UVA inside a circle. That mark means the product blocks UVA at a level of at least one third of its SPF.
The right grade for everyday life
| Situation | Recommended grade |
|---|---|
| Mostly indoors, daily commute | SPF 30+ / PA++ or higher |
| Outdoors for one to two hours | SPF 50+ / PA+++ or higher |
| Beach, hiking or skiing, long hours of strong UV | SPF 50+ / PA++++ plus waterproof |
| Overcast days or indoors | SPF 30+ / PA++ (UVA stays strong even when it is cloudy) |
Worth remembering. Even on a cloudy day, more than 90% of UVA still gets through. Thinking the sun is weak today so you can skip it is a mistake.
How much to apply, and reapplying
The labeled SPF assumes the recommended amount
SPF is measured with 2 mg of sunscreen per square centimeter of skin. For the whole face that comes to about 1.2 to 1.5 g, which is usually described as a coin-sized blob or two finger-lengths of product.
Plenty of research finds that people apply only 25 to 50% of the recommended amount on average. That is why the labeled protection often does not come through in full.
Reapplying
- Day to day, reapply every two to three hours, or right after sweating, getting wet or rubbing the skin.
- During outdoor activity, always reapply every two hours.
- After swimming, reapply even with a waterproof product once you have been exposed for more than 80 minutes (FDA standard).
Chemical filters and mineral filters
| Chemical filters | Mineral (physical) filters | |
|---|---|---|
| Common ingredients | Avobenzone, Octocrylene, Octinoxate | Zinc Oxide, Titanium Dioxide |
| How they work | Absorb UV and convert it to heat | Reflect and scatter UV at the skin surface |
| Feel | Light and clear | Can leave a white cast, can feel heavy |
| Skin irritation | Sensitive users advised to take care | Generally less irritating |
| Pregnancy and babies | Some ingredients best avoided | Largely considered safe |
