When choosing sunscreen, you see labels like "SPF50" and "PA++++." But do you truly understand what these numbers and plus signs mean?
SPF — Protection factor against UVB
SPF (Sun Protection Factor) is a measure of protection against UVB (short-wave UV: 280-315nm). UVB primarily affects the epidermis and causes sunburn (redness/erythema).
SPF 30 means that, under standardised test conditions with an even, specified application amount, the skin can be exposed to about 30 times more UV energy before sunburn occurs. It does not mean you can stay in the sun 30 times longer — real-world application amount, sweat, rubbing and time all reduce protection. In theory SPF 30 blocks about 97% of UVB and SPF 50 about 98%.
PA — Protection grade against UVA
PA (Protection Grade of UVA) is a grading system for protection against UVA (long-wave UV: 315-400nm). UVA penetrates to the dermis and destroys collagen and elastin, causing wrinkles and sagging (photoaging).
There are four levels from PA+ to PA++++, with more plus signs indicating greater UVA protection. PA+++ or higher is recommended for daily use.
Don't choose by numbers alone
SPF50+/PA++++ isn't necessarily the best choice. Higher values tend to increase the burden on skin. For daily life, SPF 30-35/PA+++ is sufficient. Choose SPF50+/PA++++ for outdoor sports and leisure activities.
The most important thing is "applying the right amount correctly and reapplying frequently". No matter how high the SPF value, effectiveness drops significantly if the amount applied is insufficient. The recommended amount for the entire face is approximately 1g (about two pearl-sized drops).
References
Key peer-reviewed sources behind the scientific statements in this article.
- Pandel R, Poljšak B, Godic A, Dahmane R. Skin Photoaging and the Role of Antioxidants in Its Prevention. ISRN Dermatol. 2013;2013:930164. PubMed