UVA sunscreen labels decoded: PA+++, the UVA circle, stars and critical wavelength

Here is the fact that undermines most sunscreen shopping: SPF is a UVB measurement. It is defined by how long skin takes to redden, and reddening is nearly all UVB. A product can be SPF 50 and offer mediocre protection against the 95% of surface UV that is UVA — the part driving photoaging, pigmentation and deep cumulative damage. Every major market has therefore bolted a separate UVA system onto the label, and no two of them work the same way.

How UVA protection is actually measured

Three test methods sit underneath every label you will encounter.

• PPD — persistent pigment darkening. An in-vivo test: skin is dosed with UVA and the tanning response is read hours later. The ratio of protected to unprotected dose is the UVA protection factor (UVA-PF). This is the basis of the PA system.
• ISO 24443 in vitro UVA-PF. Transmission through a film of product on a roughened plate, measured before and after a controlled UV dose — so it captures photodegradation, which is essential for avobenzone-based formulas. This is what the EU logo is certified against.
• Critical wavelength. The wavelength below which 90% of the product's absorbance across 290–400 nm sits. It measures the breadth of protection rather than its strength: a high critical wavelength means the absorbance extends well into the UVA, but says nothing about how much is being absorbed.

The four systems, side by side

The EU circled-UVA logo

A capital UVA inside an oval. It certifies UVA-PF at least a third of the labelled SPF, plus a critical wavelength of at least 370 nm. The scaling requirement is the clever part and the part people miss: the same logo means different things on different products. On SPF 50 it guarantees UVA-PF ≥ ~17. On SPF 15 it guarantees only UVA-PF ≥ 5. If you want strong absolute UVA protection in the EU system, you must buy a high SPF to get it.

PA+ through PA++++

Originating with the Japan Cosmetic Industry Association and now common across Asian markets, PA maps PPD-measured UVA-PF onto plus signs:

PA is the most useful of the four systems, because it is the only one stating an absolute level rather than a ratio. PA++++ means UVA-PF ≥ 16 whether the product is SPF 30 or SPF 50. If you are managing melasma or photosensitivity, PA++++ is the clearest target on any label.

Boots stars — and their catch

The UK star rating is a ratio: mean UVA absorbance divided by mean UVB absorbance, measured after irradiation. Five stars means a ratio of roughly 0.9 or better, four stars around 0.8, three around 0.6.

US "Broad Spectrum"

Since 2011, a US sunscreen may say "Broad Spectrum" if its critical wavelength is at least 370 nm. It is a single binary gate with no gradation — SPF 100 broad spectrum and SPF 15 broad spectrum carry the identical UVA claim, and there is no way to distinguish adequate from excellent UVA protection from the front of a US bottle. This is the weakest of the four systems, and it is why US shoppers who care about UVA generally end up reading the active ingredients instead.

Avobenzone and the photostability problem

Avobenzone (butyl methoxydibenzoylmethane) is the workhorse UVA-I absorber in Western sunscreens, with peak absorbance around 357 nm — right where you want it. Its weakness is that it is photounstable: on absorbing UV it can isomerise into a form that no longer absorbs. Unstabilised, it can lose on the order of half its UVA capacity within an hour of sun exposure. The sunscreen you applied is not the sunscreen you are wearing at lunchtime.

Formulators solve this, and the fix is visible in the ingredient list:

• Octocrylene — the most common stabiliser; absorbs the excited-state energy.
• Diethylhexyl 2,6-naphthalate (DEHN) — a dedicated photostabiliser.
• Bemotrizinol (Tinosorb S) — a UVA filter in its own right that also stabilises avobenzone. Doing both jobs is why it is so widely used where available.
• Polyester-8, diethylhexyl syringylidenemalonate — other proprietary stabilisers.

Two combinations to watch for:

• Avobenzone + octinoxate degrade each other. Modern formulas avoid pairing them.
• Avobenzone + zinc oxide is also a poor pairing — uncoated zinc oxide can accelerate avobenzone's breakdown. Well-formulated products either coat the zinc or use one or the other.

Practical rule: if avobenzone is on the list, look for a stabiliser on it too. If you see avobenzone with no octocrylene, DEHN or bemotrizinol anywhere in the ingredients, treat the product's UVA protection as time-limited — and reapply on schedule rather than by feel.

Which UVA filters exist, and where you can buy them

For most of the last two decades the US had the thinnest UVA toolkit in the developed world, because sunscreens are regulated there as over-the-counter drugs rather than cosmetics and no new filter cleared the process after 1999.

How to read a label in practice

1. Find the UVA mark first — circled UVA, PA rating, or stars. If there is none and the label just says "broad spectrum", you are looking at a pass/fail gate, not a level.
2. Then read the SPF, because the EU logo and the star rating are both defined relative to it. SPF 30–50 is the sensible band.
3. PA++++ if you can get it. It is the only absolute UVA guarantee on any mainstream label.
4. Check the actives. Zinc oxide, bemotrizinol, bisoctrizole and DHHB are photostable UVA workhorses. Avobenzone is excellent when stabilised and unreliable when not.
5. Add iron oxides if pigmentation is the concern — visible light is not covered by any UV filter. See UVA, melanin and pigmentation.
6. Apply enough, and reapply. Rated protection assumes 2 mg/cm², roughly a teaspoon for the face and neck; most people apply a quarter to a half of that, and protection falls off faster than proportionally.

And use it when it matters, which is more of the year than sunscreen marketing implies. UVA is high on overcast days, substantial through the winter, and present behind glass. The UVA Index is there to tell you which of those days actually warrants it.