On your sunscreen, there is the SPF, which everyone knows. And there is the PA, followed by a series of little "+" signs that few people know how to read. Yet, this is not a detail: the PA measures your level of protection against UVA rays, that silent radiation which accounts for 95% of the UV reaching your skin every day. A sunscreen without a PA indication only tells part of the story. Here is the other.
UVB vs. UVA: two types of radiation, two types of damage
The ultraviolet spectrum is divided into several bands. The two that concern us on a daily basis are UVB and UVA, and they do not act on the skin in the same way at all.
UVB: responsible for sunburn
UVB rays are short and energetic. They mainly reach the superficial layers of the epidermis and are responsible for sunburn, redness, and skin burns. This is precisely what SPF measures: the additional time you can spend in the sun before turning red, compared to unprotected skin.
UVA: deep and present all year round
UVA rays are longer and less energetic, but far more insidious. They penetrate down to the dermis, the deep layer of the skin, and cause neither immediate pain nor redness. Their action manifests over the long term, in a gradual and cumulative way.
Unlike UVB, UVA rays pass through clouds, window glass, and windshields. Their intensity varies little depending on the season or time of day. In the car, at the office behind a window, on a gray day in November: UVA rays are there. They account for 95% of the total ultraviolet radiation that reaches the Earth's surface.
The PA rating: the measurement dedicated to UVA protection
SPF only measures protection against UVB. It says nothing about your protection against UVA. It was precisely to fill this gap that the PA rating was developed.
Where does this system come from?
The PA rating was developed in Japan in the 1990s, under the aegis of the JCIA (Japan Cosmetic Industry Association). Japan was one of the first cosmetic markets to require a standardized measurement of UVA protection, independent of SPF.
To calculate this level of protection, skin is exposed to UVA rays and the time required to cause visible and persistent darkening is measured. This is called PPD (Persistent Pigment Darkening). The stronger the protection, the longer it takes to reach this threshold. The result is then converted into a number of "+" signs, from PA+ to PA++++, to be readable on packaging.
Since then, the PA system has been gradually adopted outside of Japan, notably in South Korea and Southeast Asia, before becoming widespread on European and French cosmetic packaging.
From PA+ to PA++++: what each level means in practical terms
|
PA Rating |
Corresponding PPD Factor |
UVA Protection Level |
|
PA+ |
PPD 2–4 |
Light protection |
|
PA++ |
PPD 4–8 |
Moderate protection |
|
PA+++ |
PPD 8–16 |
High protection |
|
PA++++ |
PPD 16 and above |
Very high protection |
The higher the number of "+" signs, the greater the protection against UVA rays. PA++++ currently represents the maximum level of the classification, introduced relatively recently to meet the demand for very high broad-spectrum protection products.
Why SPF alone is not enough
An SPF50 product without a PA indication can have highly variable UVA protection. Some formulas offer minimal UVA protection despite a high SPF. This is why it is recommended to check both the SPF and the PA rating (or the "broad spectrum" indication and the UVA circle on European packaging) before choosing your sunscreen.
PA and PPD: two ways of measuring the same thing
On the European market, two UVA protection rating systems coexist. They measure the same reality but express it differently.
PPD, the European reference method
PPD is the raw numerical value resulting from the UVA protection test. Concretely: a PPD of 10 means that it takes 10 times more UVA radiation to cause skin darkening with protection than without protection. The higher this number, the stronger the protection.
The PA rating simply translates this number into a "+" sign notation to make it immediately easier to read:
