SPF measures protection against UVB (sunburn), while PA measures protection against UVA (tanning and ageing) — they are two different things and should not be viewed in isolation. The higher the number after SPF, the longer the protection against sunburn; the more plus signs after PA, the stronger the ability to block UVA.
Understanding SPF
SPF (Sun Protection Factor) is an indicator of UVB blockage. SPF 30 blocks about 97% of UVB, while SPF 50 blocks about 98%. Note the increment: moving from 30 to 50 only increases protection by one percentage point, not by “60% more protection.” Therefore, for daily commuting, SPF 30 is sufficient, while SPF 50 or higher is needed for prolonged outdoor activities.
Understanding PA
PA is a UVA protection rating established in Japan, ranging from PA+ to PA++++. UVA has a longer wavelength, penetrating glass and clouds, and is the main cause of tanning, pigmentation, and photo-ageing — meaning you should apply it even on cloudy days or when indoors near windows.
| Label | What to Measure | Corresponding Issues |
|---|---|---|
| SPF 30 / 50 | UVB Protection Rate | Sunburn, Peeling |
| PA+ to PA++++ | UVA Protection Ability | Tanning, Dark Spots, Photoaging |
| Broad Spectrum | Covers UVA + UVB | Common Western Labeling Practices |
Apply Sufficient Amount for Effective Protection
The standard amount used in laboratories to measure SPF is 2 milligrams per square centimetre. This translates to roughly the size of a one-dollar coin for the entire face. Most people apply far less than this amount in daily use, so the actual protection will be lower than the number stated on the bottle — this is not a product deception, but an issue of application.
Reapplication: Sunscreen will wear off due to sweating, wiping, and time. It is generally recommended to reapply every two hours during outdoor activities; after swimming or heavy sweating, you should reapply immediately, even if it is labelled as waterproof.
Do not rely on cosmetics as a substitute: Foundations or cushions may have SPF labels, but to achieve the labelled amount, the makeup would be too thick to be practical. Treat it as an additional layer of protection, not the sole sunscreen.
Frequently asked
What is the difference between SPF and PA?
SPF measures protection against UVB, the rays that cause sunburn. PA measures protection against UVA, which drives tanning, pigmentation and photo-ageing. They are two different things and should not be read in isolation.
Is SPF 50 much better than SPF 30?
No. SPF 30 blocks about 97% of UVB and SPF 50 about 98% — one percentage point, not the “60% more protection” the numbers suggest.
How much sunscreen should I actually apply?
Laboratories measure at 2 milligrams per square centimetre, which works out at roughly a one-dollar-coin amount for the face. Most people apply far less, so real-world protection sits below the labelled figure.
How often should I reapply?
Every two hours outdoors, and immediately after swimming or heavy sweating even if the product is labelled waterproof.
Does foundation with SPF count as sunscreen?
Treat it as an extra layer rather than your only protection. Reaching the labelled amount through makeup alone would require an impractically thick application.