This is a very good question. (initially answered on Quora)
To understand this complex topic, let’s first discuss what actually is sun damage and what constitutes sun protection.
Sun Damage is literally caused by UV radiation (UVR). UVR are emitted from the sun along with accompanying visible light rays. UVR leads to skin damage as it is both cytotoxic (injures and kills cells) and mutagenic (DNA mutation). As such, you can now appreciate how prolonged and excessive sun exposure can lead to:
– skin aging (cytotoxic)
– skin cancer (mutagenic)
The process of how UVR leads to DNA mutation which eventually causes skin cancer is very well elaborated in literature. To keep it short, UVR generates oxidative radicals that result in breaks throughout DNA structures. These breaks can lead to reactive DNA repairs or cell deaths, but it is these imperfect and subpar DNA repairs that can lead to mutations that produce cell immortality and dysfunctional cellular regulation. Eventually, the cell/tissue becomes cancerous.
Right now, we have established how UVR is the main culprit for skin damage and skin cancer. So, the natural pathway for any form of sun protection is to limit UVR, correct?
Protective Roles of Melanin:
It is a fact that people with darker skin (higher dermal concentration of melanin) have better protection from sun damage. It is also true vice versa.
- acts as a physical barrier to scatter UVR
- is an absorbent filter that reduces UVR penetration through the skin
When you talk about “reflecting” light, I believe you are confusing UVR from Visible Light.
For skin related testing and scanner,