UV radiation is not the sun itself. Understanding the difference changes how we protect our skin.
Ultraviolet radiation is a range of electromagnetic energy beyond the visible light spectrum. We cannot see it. Most of us cannot feel it directly. And it causes more skin damage annually than anything else we put on our skin — or fail to put on it.
Not heat. Not visible light. A separate band.
Ultraviolet radiation is a range of electromagnetic energy beyond the visible light spectrum. We cannot see it. Most of us cannot feel it directly. And it causes more skin damage annually than anything else we put on our skin — or fail to put on it.
There are three UV bands. UVC is absorbed almost entirely by the atmosphere and does not reach us at ground level. UVA and UVB both do — and they behave differently.
Two wavelengths, two damage mechanisms.
UVA is long-wave ultraviolet. It constitutes approximately 95% of the UV radiation that reaches Earth’s surface. It penetrates deeply into the skin, reaches the dermis, causes oxidative damage, accelerates structural breakdown, and is present year-round, from sunrise to sunset, through clouds, and through glass. It does not cause sunburn. It causes the category of damage that accumulates invisibly over time — and it is the primary UV driver of PIH worsening.
UVB is short-wave ultraviolet. It is more intense during summer months and at higher altitudes, and it is what causes sunburn. It is also what most SPF testing actually measures. SPF — Sun Protection Factor — is a UVB metric. A product labeled SPF 50 tells us how it performs against UVB. It tells us nothing specific about UVA unless the label also reads “broad spectrum.”
Any brightening active working on a dark mark loses ground every morning that UV reaches healing skin without protection.
Deep melanin deflects some UV. It does not stop it.
The assumption that melanated skin does not need SPF comes from a partial truth. Our skin does produce more melanin in response to UV exposure — the tanning mechanism — and melanin does absorb and scatter some UV. Fitzpatrick V–VI skin has more melanin and therefore marginally more natural deflection than Type I skin.
What melanin does not do is prevent UV from reaching the melanocytes. It does not stop UVA from penetrating. It does not prevent the melanocyte activation that follows UV exposure and worsens hyperpigmentation. Our skin is not protected from UV by virtue of being dark. It is more efficient at tanning in response to UV — and that same melanocyte activation, triggered during or after any inflammatory event, is what makes every PIH mark harder to resolve.
Our skin is not protected from UV by virtue of being dark. It is more efficient at tanning in response to UV — and more prone to the PIH that follows. Doctor Djeli
The mechanism is direct.
When skin is healing from an inflammatory event — a razor bump, a breakout, a friction mark — the melanocytes in the affected area are already active. They are already producing excess pigment. UV exposure during this healing window signals the melanocytes again. More pigment. Deeper mark. Longer resolution.
This is why SPF matters more during active PIH treatment, not less. Any brightening active working to interrupt the melanin pathway — azelaic acid, niacinamide, tranexamic acid — loses ground every morning that UV reaches healing skin without protection. The investment in those actives pays off only when we stop adding to the problem.
The label requirement. And what it does not tell us.
In the United States, a product labeled “broad spectrum” meets FDA requirements for UVA protection in addition to the UVB protection SPF measures. Broad spectrum is the baseline. Not the ideal — the floor.
What broad spectrum does not tell us: how much UVA protection. The FDA’s testing method for UVA is less specific than the UVB/SPF system, and a product can carry the broad spectrum label with UVA protection considerably lower than its SPF would suggest. The PA+ system used in Japan and Korea (and increasingly on products sold through Korean skincare channels) is a more granular UVA rating — PA++++ is the highest level. When choosing between two broad-spectrum products, the PA rating is worth reading.
For Fitzpatrick IV–VI skin, the practical minimum is SPF 30 broad spectrum, applied every morning as the last skincare step, reapplied every two hours during extended outdoor time. Not a summer protocol. Not a beach protocol. A daily protocol, because UVA is present every day and comes through the window.
UV radiation isn't the same thing as the sun's heat or light — it's an invisible band you can't see or usually feel, and it does more damage to skin over a year than almost anything else. UVA is the one that matters most day to day: it's most of the UV that reaches you, it penetrates deep, and it comes through year-round, through clouds, and through window glass, so it's not a summer problem or a beach problem. UVB is the one that burns you, and it's also the one SPF actually measures, which is why a high SPF number tells you nothing about UVA unless the label also says broad spectrum. Having more melanin doesn't shield you from this — it means your skin tans faster in response to UV, and that same reaction is what redarkens a mark that's still healing. The daily minimum is broad spectrum SPF 30, worn every day, not just outdoors.
Reign in your skin
SPF is not just for people who burn. UV worsens PIH regardless of skin tone.
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