Ultraviolet Radiation Effects on Skin, Eyes, Immunity, and DNA

Ultraviolet radiation (UVR) is non-ionizing electromagnetic radiation (100–400 nm) with profound biological effects.

Target Organs & Pathology

1. Skin:
   • UVB (280–315 nm): Epidermal damage → sunburn (erythema), direct DNA damage (CPDs, 6-4PP), squamous cell carcinoma (SCC), basal cell carcinoma (BCC).
   • UVA (315–400 nm): Deeper dermal penetration → oxidative stress (ROS), collagen/elastin degradation (photoaging, wrinkles), indirect DNA damage, melanoma contribution.
   • Chronic: Actinic keratosis, poikiloderma, immunosuppression.
2. Eyes:
   • Photokeratitis (corneal "sunburn"), photoconjunctivitis.
   • Cataracts (cortical, posterior subcapsular) — UVB.
   • Pterygium, pinguecula — UVB/UVA.
   • Macular degeneration — UVA/blue light.
3. Immune System:
   • UVR → cis-urocanic acid → systemic immunosuppression (↓ antigen presentation, ↑ Tregs).
   • Reactivates latent herpes simplex (cold sores).
   • Reduces vaccine efficacy, tumor surveillance.
4. DNA:
   • Direct: Cyclobutane pyrimidine dimers (CPDs), (6-4) photoproducts → C→T mutations (p53).
   • Indirect: ROS → 8-oxoguanine, strand breaks.
   • Repair: Nucleotide excision repair (NER); defective in xeroderma pigmentosum.

Protection Hierarchy

1. Avoid peak UV (10a–4p).
2. Protective clothing (UPF 50+), wide-brim hat.
3. Broad-spectrum sunscreen (SPF 30+), reapplied q2h.
4. Sunglasses (UV400, wraparound).
5. Shade structures.

No safe tan. UVR is a complete carcinogen (initiator + promoter).