Keratin vs. Melanin: What Actually Protects Skin from UV Radiation

Keratin does not meaningfully protect against UV radiation.

Keratin's Actual Role

• Structural protein (intermediate filaments) in keratinocytes.
• Provides mechanical strength, barrier integrity, waterproofing (with lipids).
• Forms stratum corneum — physical barrier, not photoprotective.

Melanin: The True Photoprotectant

• Produced by melanocytes (neural crest-derived) in basal epidermis.
• Packaged in melanosomes → transferred to keratinocytes.
• Eumelanin (brown/black): Absorbs/scatters UVR, quenches ROS, protects nuclear DNA.
• Pheomelanin (red/yellow): Less protective; can generate ROS under UV.

UV Defense Layers

1. Stratum corneum: Reflects/scatters ~5–10% UVB.
2. Melanin cap over nuclei: "Supranuclear cap" shields DNA — primary defense.
3. DNA repair: Nucleotide excision repair (XPC, TFIIH) fixes CPDs/6-4PPs.
4. Antioxidants: Enzymatic (SOD, catalase, GPx) + non-enzymatic (vit C, E, glutathione).
5. Apoptosis: Heavily damaged keratinocytes → sunburn cells.

Clinical Implication

Fitzpatrick skin type (I–VI) = melanin content/distribution → UV sensitivity & skin cancer risk. Sunscreen (broad-spectrum, SPF 30+) supplements, not replaces, melanin.