PlayInfoBox

Home /Beauty /Sunscreen SPF and PA Ratings Explained

Sunscreen SPF and PA Ratings Explained

SPF and PA are the two rating systems most sunscreen labels use, and they measure two different kinds of sun protection.

SPF measures UVB protection

SPF (Sun Protection Factor) estimates how much longer skin can be exposed to UVB rays, the type mainly responsible for sunburn, before burning compared to unprotected skin. It does not directly measure protection against deeper-penetrating UVA rays.

Higher SPF numbers have diminishing returns

Going from a low to a moderate SPF blocks noticeably more UVB radiation, but climbing from an already-high SPF to an even higher one adds a much smaller additional percentage, since no sunscreen blocks all UV rays regardless of the number on the label.

PA measures UVA protection

PA (Protection Grade of UVA), a rating system that originated in Japan and is now common across much of Asia, uses a scale of plus signs β€” commonly from PA+ up to PA++++ β€” where more plus signs indicate stronger protection against UVA rays, which are linked more to skin aging and are less addressed by SPF alone.

"Broad spectrum" means both UVA and UVB

In markets that do not use the PA scale, a label reading "broad spectrum" is the main signal that a sunscreen has been tested to protect against both UVA and UVB, rather than UVB alone.

Reapplication matters as much as the number

Any SPF or PA rating reflects protection at the moment of a specific, fairly generous application, not for an entire day. Sweating, swimming, and time passing all reduce effective protection, which is why reapplying every couple of hours during extended sun exposure is commonly recommended.

Why two different rating systems exist

SPF became the standard measurement of UVB protection long before UVA damage was as well understood, so it was never designed to describe UVA protection at all. The PA scale was developed later specifically to fill that gap, which is why some sunscreen labels show both ratings side by side instead of just one.

A high number is not the whole story

Texture, how evenly a product is applied, and how often it is reapplied all affect real-world protection at least as much as the SPF or PA number printed on the bottle. A high-SPF sunscreen applied thinly once in the morning can end up protecting less over a full day than a lower-SPF product reapplied properly.

Frequently Asked Questions

Is SPF 100 twice as protective as SPF 50?

No. The percentage of UVB rays filtered rises much more slowly than the SPF number itself, so the practical difference between a high SPF and a very high SPF is fairly small β€” reapplication habits generally matter more than chasing the highest number available.

Do I need to check for a PA rating if my local products only list SPF?

Many products sold where PA is not the local standard use "broad spectrum" wording instead to indicate UVA coverage, so checking for that phrase serves a similar purpose to checking a PA rating on a differently labeled product.