What does UV radiation actually do to your skin?
UV Radiation and Your Skin — What Is Actually Happening and Why Sun Protection Is Non-Negotiable
The single most important thing you can do for your skin has nothing to do with serums, treatments, or injectables. Here is the honest science behind why.
The most important sentence in skincare
If you could do only one thing for your skin — one intervention with the greatest evidence base for preventing ageing and protecting long-term skin health — it would not be a retinoid, a biostimulator, or any advanced treatment. It would be daily, broad-spectrum, high-factor sun protection, applied consistently, every day, regardless of weather or season..
Everything else in a skincare routine is supplementary to sunscreen. Without SPF the value of everything else is significantly undermined.
What does UV radiation actually do to your skin?
Ultraviolet radiation reaches the skin in two forms, and they damage it in distinct ways.
UVB acts primarily on the surface layers of the skin. It is the main cause of sunburn, and its most significant long-term consequence is direct damage to the DNA in skin cells producing structural distortions that, if not repaired before the cell divides, can accumulate into the mutations that underlie skin cancer.
UVA penetrates considerably deeper, reaching the dermis where collagen and elastin live. Its primary mechanism of damage is the generation of reactive free radicals that attack the structural proteins of the skin and activate the enzymes responsible for breaking collagen down.
Both UVA and UVB activate matrix metalloproteinases, the collagen-degrading enzymes we have written about in detail in the companion Clinical Perspectives piece on this subject and simultaneously suppress the signals that drive new collagen synthesis. The result is a double assault: collagen breaks down faster and is replaced more slowly.
Photo-ageing versus chronological ageing
The changes produced by cumulative UV exposure are distinct from the changes produced by time alone and they are considerably more severe.
Photoaged skin has a characteristic appearance that histologists can identify under the microscope. The dermis is infiltrated by disorganised, abnormal elastic material that has replaced degraded collagen - it is the hallmark finding. It does not occur in sun-protected skin of the same age.
The damage is also cumulative and largely irreversible. Each episode of unprotected UV exposure adds to an accumulating burden that the skin's own repair mechanisms cannot fully correct. The good news, and it is genuine good news, is that stopping or significantly reducing UV exposure at any point slows the rate of further damage. It is never too late to benefit from sun protection, even in skin that has already accumulated significant photodamage.
Sunscreen, SPF — what the number means and why it matters
The sun protection factor measures a sunscreen's ability to protect against UVB-induced sunburn. An SPF of 50 allows approximately 2% of UVB to penetrate — but this figure assumes the product is applied at the quantity used in laboratory testing, which is considerably more than most people use in practice.
Under-application is the norm, not the exception, which is one reason that using a higher SPF partially compensates for real-world application habits.
Broad-spectrum designation, covering both UVA and UVB, is not optional. A product that only protects against UVB prevents sunburn but allows UVA to continue driving collagen degradation in the dermis unimpeded. Broad-spectrum, SPF 50 or above, applied as the final step of your morning routine, is the appropriate daily standard.
The role of antioxidants
Sunscreen filters reduce the UV that reaches the skin but they do not eliminate it entirely. Even beneath an effective sunscreen, some reactive oxygen species are generated. This is where antioxidants provide a complementary layer of protection.
Vitamin C is the most clinically significant topical antioxidant in this context. It neutralises the free radicals generated by UV exposure, and simultaneously supports collagen synthesis as an essential cofactor in its production. Applied beneath your SPF in the morning, it creates a dual protective layer that addresses both the oxidative damage and the structural consequences of the UV that gets through.
Vitamin E works synergistically with vitamin C — the two regenerate each other's antioxidant capacity in a cycle that produces greater combined protection than either achieves alone. Many well-formulated SPF products now incorporate both.
Niacinamide supports DNA repair pathways that reduce the persistence of UV-induced lesions, and its anti-inflammatory properties reduce the chronic inflammatory component of photodamage.
The practical morning routine
The evidence converges on a straightforward protocol that, applied consistently, represents the most effective daily defence against photoageing available:
A vitamin C serum applied to clean skin,
Followed by SPF 50 broad-spectrum sunscreen as the final step.
In the evening, a retinoid, the most comprehensively evidenced topical ingredient for both preventing further photodamage and partially reversing existing damage, addresses the collagen deficit that UV exposure drives during the day. Read why retinoids are the skincare ingredient that nothing has yet replaced.
This combination of vitamin C, SPF, and retinoid is the foundation on which everything else is built. Biostimulatory treatments, dermal fillers, and advanced skincare ingredients all produce better and longer-lasting results in skin that has this foundation consistently in place.
A plain statement worth making
The bottled sunscreen sitting in your bathroom, applied daily without fail, will do more to preserve your skin over the next decade than any combination of treatments available in any clinic. That is not a modest claim. It is what fifty years of peer-reviewed dermatological research consistently supports.