PPD stands for Persistent Pigment Darkening, and it's one of the more overlooked numbers on a sunscreen label, mostly because SPF gets all the attention. But SPF is primarily a measure of UVB protection, so the number alone doesn't tell you how well a sunscreen handles UVA, and that's exactly the gap PPD is designed to fill.
What SPF Actually Measures
SPF, or Sun Protection Factor, is primarily an indicator of UVB protection, the rays mostly responsible for sunburn. It's a useful number, but an incomplete one, since UVB isn't the only type of UV radiation reaching your skin.
What UVA Rays Do Differently
UVA rays penetrate deeper into the skin than UVB, and they're the main driver of tanning, premature aging, fine lines, and longer-term skin damage that doesn't show up as an immediate sunburn. UVA also passes through clouds and glass more easily than UVB, part of why "I'm indoors, I don't need SPF" doesn't fully hold up.
Since SPF is primarily a UVB measurement, a sunscreen could carry an impressively high SPF number and still leave meaningful questions about UVA protection unanswered, unless that's addressed separately through UVA-specific testing or a broad-spectrum claim.
What PPD Actually Measures
PPD is an in-vivo method used to measure UVA protection by assessing the skin's persistent pigment darkening response after UVA exposure. The resulting UVA protection factor indicates how much UVA exposure is required to produce the same pigment-darkening response with sunscreen applied, compared to unprotected skin. The higher that measured factor, the more UVA protection the formula is providing.
How PPD Relates to PA Ratings
PPD and PA are closely related, but they're not the same thing. PPD refers to an in-vivo method used to determine UVA protection specifically. PA is a grading system used within Asian sunscreen labeling systems (PA+ through PA++++) to communicate UVA protection using plus signs instead of a raw number. The exact relationship between a numerical UVA protection result and a specific PA grade depends on which testing standard is being used, so PA isn't simply "PPD renamed," it's a related but distinct way of communicating UVA protection to the consumer.
What PPD, PA, and SPF Each Actually Tell You
|
Rating |
Mainly Tells You |
What It Relates To |
|
SPF |
UVB / sunburn protection |
UVB |
|
PPD / UVA-PF |
Numerical UVA protection measurement |
UVA |
|
PA+ to PA++++ |
UVA protection grade |
UVA |
Why This Distinction Actually Matters
A sunscreen can be excellent at preventing sunburn (high SPF) while giving you very little information about how it performs against UVA specifically. Broad spectrum is a separate labeling claim used to indicate protection across both UVA and UVB, the exact testing requirements depend on the regulatory market.
If a sunscreen only lists an SPF number with no PA rating and no PPD figure, that doesn't automatically mean weak UVA protection, it may simply be communicating UVA protection through a broad-spectrum claim instead. Either way, it's worth checking for some explicit UVA indicator rather than assuming SPF alone covers it.
What to Actually Look For on a Label
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A PA rating (PA+ through PA++++) if the sunscreen follows the Asian labeling convention, higher pluses generally indicate stronger UVA protection within that grading system
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An explicit "broad spectrum" claim, which in most regulated markets signals the product has been tested for effectiveness against both UVA and UVB
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Both an SPF number and some UVA-specific indicator together, rather than relying on SPF alone as a stand-in for total protection
The Daily Call Sun Serum carries an SPF 50 PA++++ rating, using the PA system to communicate a high level of UVA protection alongside its SPF rating for UVB-related protection. If you're comparing formats and finishes, the sunscreen collection has the full range.
Frequently Asked Questions
Is PPD the same as PA rating? They're closely related but not identical. PPD is an in-vivo method used to measure UVA protection, PA is a grading system that communicates UVA protection using plus signs, often informed by PPD-related testing, though the exact relationship depends on the standard used.
Can a sunscreen have high SPF but limited UVA protection? Yes, that's possible, since SPF is primarily a UVB measurement and doesn't directly tell you the level of UVA protection, which is why checking for a PA rating or broad-spectrum claim matters as a separate step.
Is a higher PPD always better? Generally, higher measured UVA protection is preferable, but PPD isn't the only way UVA protection gets evaluated, a sunscreen should still be judged on its overall broad-spectrum protection and correct, consistent application.
What does PA++++ mean compared with PPD? PA++++ represents a high UVA protection category within the PA grading system, but it doesn't give you the exact numerical UVA protection factor, meaning two different PA++++ products can still have somewhat different measured UVA protection levels.
Why don't all sunscreens show a PA rating? PA ratings are most common on sunscreens formulated to Asian regulatory standards, particularly Korean and Japanese systems. Sunscreens formulated for other markets often use broad-spectrum claims or other UVA indicators instead.