UV Light and Photoaging: Skin's Number 1 Enemy

UV spectrum: UVA, UVB, UVC

Approximately 95% of the UV light reaching the Earth from the sun is UVA, and 5% is UVB. UVC is blocked in the ozone layer and never comes into contact with the skin (as far as it comes from the sun). UVB has a short wavelength, penetrates the epidermis and upper dermis; it is responsible for sunburn and most skin cancers. UVA has a long wavelength, penetrates deeper, and is the main aging factor for the skin. UVA can pass through glass, clouds, and shade — so it also manifests itself in cloudy weather.

Photoaging mechanism

UV ages the skin in three main ways. First, direct DNA damage: UVB wavelength creates "thymine dimers" in DNA; if these damages are not repaired, either the cell dies or mutations accumulate. Second, free radical production: UVA produces reactive oxygen species (ROS) in skin cells; these molecules attack lipids, proteins, and DNA. Third, matrix metalloproteinase (MMP) activation: UV causes fibroblasts to secrete collagen-degrading enzymes; new collagen synthesis also decreases.

When these three mechanisms work together, 10 years of continuous UV exposure can age the skin an extra 10-15 years. Classic study: one of identical twins was excessively exposed to the sun, the other was not — the difference can be a 20-30 year appearance difference.

Blue light (HEV) and digital life

HEV — high-energy visible light — is visible light in the blue and violet range. It comes from screens, LED lighting, and daylight itself. Studies over the last 10 years show that HEV triggers melanogenesis (pigmentation), especially increasing spotting in darker skin types. A modern patient who looks at their phone all day, especially if they have a history of melasma (pregnancy mask), is recommended to switch to an SPF with HEV protection (iron oxide or pigmented mineral SPFs).

Misconceptions about SPF

The phrase "there is no difference between SPF 50 and SPF 30" is a myth I often hear in my clinic. On the surface, the percentage difference is small (97% vs 98%), but this 1% difference accumulates over hours, creating a measurable difference in protection. Also, no user applies the recommended amount (2 mg/cm²) exactly; most of us apply half as much. SPF 50 absorbs this real-world deficit.

UVA protection is as important as SPF selection. If there is PA+++, PA++++ or the European "UVA circular logo", UVA protection is sufficient. American products have the "broad spectrum" label but do not specify the UVA-PF value — European products are more transparent in this regard.