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UVA and UVB are two parts of ultraviolet sunlight, and your sunscreen should protect against both. UVB is a major cause of sunburn; UVA contributes substantially to cumulative skin changes and can pass through some glass. Both can damage skin. “Broad spectrum” is the U.S. label term to look for alongside SPF.
| Question | UVA | UVB |
|---|---|---|
| Common association | Photoaging and pigmentation; also contributes to skin cancer risk. | Sunburn; also contributes to skin cancer risk and aging. |
| Typical penetration in skin | Reaches more deeply than UVB. | Acts mainly in more superficial skin layers. |
| Does ordinary glass stop it? | Some glass transmits a meaningful amount; construction and coatings matter. | Ordinary window glass generally blocks much more UVB. |
| What should you read on sunscreen? | Broad-spectrum labeling, rather than the SPF number alone. | SPF provides the main sunburn-protection measure. |
The familiar “A for aging, B for burning” shortcut is only a memory aid. It should not be read as saying that each wavelength has just one effect. Nor does a day without visible redness prove that exposure has been harmless.
In the United States, the claim depends on testing the finished sunscreen. FDA labeling and testing guidance explains the UVA coverage requirement as well as SPF testing. A broad-spectrum label signals protection across the UV range; it does not tell you that two products with the same SPF have identical performance at every wavelength.
For everyday selection, use broad-spectrum SPF 30 or higher and suitable water resistance. European UVA symbols and PA ratings come from other labeling systems and should not be casually converted into a precise U.S. SPF equivalent.
SPF is primarily about sunburn protection. A high SPF alone is insufficient information: confirm that the product also says broad spectrum. Likewise, spotting zinc oxide, avobenzone or another familiar filter does not establish the tested performance of the complete formula.
Visible light is outside the UV range. For people whose pigmentation is aggravated by sunlight, particularly those with darker skin tones or melasma, a suitable tinted sunscreen with iron oxides may be helpful. SPF and broad-spectrum claims do not themselves specify a visible-light protection rating.
Use the guide to tint and iron oxides to separate those functions. Sunscreen supports prevention of further darkening; existing pigmentation may need a separate plan.
For the practical differences between a desk away from daylight, a sunny window and a car commute, see sunscreen indoors. For visible aging, see photoaging and collagen changes.
By Herbal Dynamics Beauty · Updated September 26, 2026
