Skin Color Biology: Melanin, Genetics & UV Protection

Melanin – The Pigment

• Produced by melanocytes in basal epidermis.
• Two main types: Eumelanin (black/brown, photoprotective) and Pheomelanin (red/yellow, less protective, generates ROS).
• Packaged in melanosomes → transferred to keratinocytes → forms "melanin cap" over nucleus.

Genetic Determination

• Polygenic (dozens of loci: MC1R, TYR, OCA2, SLC24A5, SLC45A2, MFSD12, DDB1, etc.).
• Additive effects → continuous variation.
• Evolutionary selection: UV-B (vitamin D synthesis) vs. UV-B/UV-A (folate degradation, DNA damage).

Photoprotection Mechanism

• Absorbs/scatters UVR (UV-B > UV-A).
• Scavenges free radicals.
• Eumelanin SPF equivalent ~1.5–2 per unit melanin index; high eumelanin ≈ SPF 10–15 intrinsic.
• Does not block all UV; DNA damage still occurs → sunscreen needed for all skin types.

Clinical Implications

• Fitzpatrick Skin Phototypes I–VI classify UV response (burn vs. tan).
• Skin cancer risk inversely correlates with constitutive pigmentation.
• Vitamin D synthesis efficiency lower in darker skin → higher supplementation needs at high latitudes.
• Pigmentary disorders: vitiligo, melasma, albinism, post-inflammatory hyperpigmentation.