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Most sunscreen labels carry two separate ratings, and it is common to treat them as one number. SPF and PA are not measuring the same thing, and understanding the difference changes how you read a bottle at the drugstore.
SPF measures UVB, not everything
SPF stands for Sun Protection Factor, and it is a measure of protection against UVB rays specifically. UVB is the wavelength most responsible for sunburn and plays a major role in skin cancer risk. The SPF number is a rough indicator of how much longer your skin can be exposed to UVB before burning, compared to no protection at all, under laboratory testing conditions that rarely match real life.
An SPF of 30 is often described as blocking about 97 percent of UVB rays, while SPF 50 blocks slightly more. The jump from 30 to 50 is smaller than the numbers suggest. Neither one blocks all UVB rays, and no sunscreen blocks 100 percent.
Why the percentage gap matters less than application
The difference between SPF 30 and SPF 50 in real-world protection is minor compared to the difference between applying enough product and applying too little. Lab testing uses a specific amount of product per square inch of skin, and most people apply far less than that in daily life. A high SPF number applied thinly can perform worse than a moderate SPF number applied correctly.
PA measures UVA
PA stands for Protection Grade of UVA, a rating system that originated in Japan and is now common on sunscreen labels sold in the United States, particularly from Asian beauty brands. UVA rays penetrate deeper into the skin and are linked to premature aging, loss of elasticity, and pigmentation changes. UVA is present at consistent levels throughout the year and passes through window glass, which UVB largely does not.
The PA scale uses plus signs, ranging from PA+ to PA++++. More pluses indicate a higher degree of UVA protection as measured by a test called the Persistent Pigment Darkening method. A sunscreen labeled PA++++ offers the highest tier of UVA protection currently rated under this system.
Why both numbers matter together
A sunscreen can have a high SPF and a low PA rating, or the reverse. SPF alone tells you nothing about UVA coverage. If a product only lists SPF with no PA or no broad-spectrum claim, you have information about burn protection but not about the aging and pigmentation risks tied to UVA. Products sold in the United States that say “broad spectrum” have passed a UVA protection test required by the FDA, even without a PA rating attached, so that label is a reasonable substitute when PA is not listed.
Broad spectrum and PA ratings are answering the same underlying question through different labeling systems. Neither one is optional if UVA-related concerns like pigmentation or fine lines are part of what you are trying to manage.
What the numbers do not tell you
Neither SPF nor PA accounts for how sweat, water, touching your face, or friction from a mask or collar wears down the product over the course of a day. Both ratings come from controlled lab conditions with a fixed amount of product, applied once, on skin that is not moving or being touched. Real days involve all of those variables, which is part of why reapplication matters regardless of the number on the label.
The ratings also do not describe texture, how a product wears under makeup, or whether it will cause breakouts on a particular skin type. Those are separate considerations that require testing a product on your own face, not reading the label more carefully.
A practical way to read a label
Look for a combination: an SPF of 30 or higher, a broad-spectrum claim or a PA rating of at least PA+++, and a texture you will actually reapply without resenting it. A sunscreen with excellent numbers that sits in a drawer unused is not providing protection. The best-rated product is the one that gets applied in the right amount and reapplied on the schedule your day actually requires.
Why some labels only show one rating
Not every sunscreen sold in the United States carries a PA rating, since it is not a requirement under FDA rules the way SPF and broad-spectrum testing are. A product formulated and labeled primarily for the U.S. market may rely solely on the broad-spectrum designation to communicate UVA protection, while a product imported from or formulated for markets like Japan or South Korea is more likely to carry a PA rating alongside SPF. Seeing only one of the two ratings on a label is not automatically a red flag, but it does mean checking for the other type of claim, whether that is broad spectrum wording or a PA symbol, before assuming a product covers both UVB and UVA.
Reading ingredient lists as a backup
When a label is unclear or a rating is missing, the active ingredient list can offer a secondary check. Filters like zinc oxide, titanium dioxide, and avobenzone are associated with broader UVA coverage, while a formula built primarily around older UVB-focused filters may leave more of a gap on the UVA side even with a high SPF number. This is not a substitute for reading the broad-spectrum or PA claim directly, but it is a useful cross-check when a label feels incomplete or ambiguous.
The bottom line
SPF and PA are two different measurements answering two different questions, one about burn risk from UVB and one about deeper UVA exposure. Reading both, rather than defaulting to the highest SPF number on the shelf, gives a more complete picture of what a sunscreen is actually doing for your skin. When only one rating is listed, checking for a broad-spectrum claim or scanning the active ingredients fills in the rest of the picture.
