Photoprotection

UV Radiation & Skin - Sunny Side Effects

• UV Spectrum & Penetration:
  • UVC (100-280 nm): Mostly ozone-absorbed.
  • UVB (280-320 nm): Epidermis. 📌 "B" for Burn, DNA damage, Vit D.
  • UVA (320-400 nm): Dermis. 📌 "A" for Aging, Tanning.
    • UVA1 (340-400 nm); UVA2 (320-340 nm, also erythrogenic).
• Acute Skin Damage:
  • Sunburn (Erythema): UVB primary. Peaks 12-24 hrs.
  • Tanning: Immediate Pigment Darkening (IPD) (UVA), Delayed Tanning (UVB/UVA).
• Chronic Skin Damage:
  • Photoaging: Wrinkles, solar elastosis, lentigines (UVA > UVB).
  • Photocarcinogenesis: Actinic keratosis, Squamous Cell Carcinoma (SCC), Basal Cell Carcinoma (BCC), Melanoma (UVB major, UVA contributes).

⭐ UVB is approximately 1000 times more erythemogenic than UVA radiation.

Sunscreens Explained - Shield Up Science

• Types & Mechanisms:
  • Physical (Mineral): ZnO, TiO2. Reflect/scatter UV. Broad spectrum. Good for sensitive skin.
  • Chemical (Organic): Oxybenzone, Avobenzone. Absorb UV, convert to heat.
  • Hybrid: Combine physical & chemical filters.
• Efficacy Measures:
  • SPF (Sun Protection Factor): UVB protection. Min. SPF 30 (~97% UVB block) recommended.
  • PA System: UVA protection (e.g., PA+, PA++, PA++++). Prevents photoaging.
  • Broad Spectrum: Essential for UVA/UVB coverage.
• Application Essentials:
  • Amount: 2 mg/cm². (📌 Teaspoon Rule: ~1/2 tsp for face/neck).
  • Timing: Apply 15-30 min before sun exposure.
  • Reapply: Every 2-3 hrs; after swimming/sweating.
  • Water Resistance: Check label (40/80 min).

⭐ "Broad Spectrum" designation indicates protection against both UVA (aging) and UVB (burning) rays, which is critical for comprehensive skin protection.

Beyond Sunscreen - Shade & Smarts

• Physical Barriers are Key:
  • Clothing:
    • Darker colors, tightly woven fabrics (e.g., denim, polyester) offer superior protection.
    • Look for Ultraviolet Protection Factor (UPF) >30; UPF 50+ is excellent.
  • Hats: Broad-brimmed (>3 inches or 7.5 cm) shielding face, ears, and neck.
  • Sunglasses: UV 400 label, wrap-around design to block 99-100% UVA/UVB rays.
• Smart Sun Habits:
  • Seek shade: Especially during peak UV intensity (10 AM - 4 PM).
  • Be mindful of reflective surfaces: Sand, water, snow ↑ UV exposure.
• Additional Shields:
  • UV-protective window films for cars/homes.

⭐ Wetting a fabric usually ↓ its UPF value, especially cotton. Dry clothing is more protective.

Special Cases - Sensitive Skin Savvy

• Children:
  • < 6 months: Primarily shade & protective clothing. Physical sunscreens (ZnO, TiO₂) if unavoidable on small, exposed areas.

  • 6 months: Broad-spectrum, water-resistant SPF ≥ 30 (physical preferred). Reapply q2h.

• Photosensitive Disorders (e.g., SLE, Porphyrias, XP):
  • Strict, year-round photoprotection essential.
  • High SPF (50+), broad-spectrum (UVA-PF critical).
  • Visible light protection (e.g., tinted iron oxide) for some conditions.
  • XP: Meticulous UV protection; high skin cancer risk.
• Drug-Induced Photosensitivity:
  • Identify/stop culprit. Key drugs: Tetracyclines (Doxycycline), NSAIDs, Thiazides, Sulfonamides, Amiodarone. 💡 Advise strict broad-spectrum photoprotection.
• Post-Procedure Skin (lasers, peels):
  • Strict sun avoidance. Gentle, physical sunscreens.

⭐ For children < 6 months, the primary photoprotection strategy is avoidance of direct sun exposure and use of protective clothing; sunscreens are secondary and physical blockers preferred.

High‑Yield Points - ⚡ Biggest Takeaways

• Sun Protection Factor (SPF) primarily measures protection against UVB-induced erythema.
• Broad-spectrum sunscreens offer protection against both UVA and UVB radiation.
• Physical sunscreens (e.g., zinc oxide, titanium dioxide) work by reflecting and scattering UV light.
• Chemical sunscreens (e.g., oxybenzone, avobenzone) absorb UV radiation and convert it to heat.
• Photopatch testing is crucial for diagnosing photoallergic contact dermatitis from sunscreens.
• UPF (Ultraviolet Protection Factor) in clothing indicates UV protection; UPF 50+ is recommended.
• Advise sunscreen application 15-30 minutes before sun exposure, with reapplication every 2-3 hours.