Light-Based Therapies

Light Physics & Skin Optics - ✨ Shedding Light

• Electromagnetic Spectrum (EMS): Lasers utilize specific UV, visible, or infrared light wavelengths.
• Key Parameters:
  • Wavelength ($\.lambda$): Governs penetration depth & chromophore targeting.
  • Fluence: Energy density ($J/cm^2$).
  • Pulse Duration (PD): Exposure time; critical for selective heating. Must be < target's Thermal Relaxation Time (TRT).
• Selective Photothermolysis:
  • Matching $\.lambda$, PD, and fluence to precisely target chromophores, sparing adjacent tissue.

  ⭐ Anderson and Parrish's principle of selective photothermolysis is foundational to dermatologic laser therapy.

• Key Chromophores (Light Absorbers):
  • Melanin: Hair, pigmented lesions (e.g., 755 nm Alexandrite).
  • Hemoglobin: Vascular lesions (e.g., 585/595 nm PDL).
  • Water: Skin resurfacing (e.g., CO2 10600 nm, Er:YAG 2940 nm).
  • Tattoo Ink: Exogenous pigments with varied absorption spectra.

Lasers in Dermatology - 🎯 Zap & Renew

• Ablative Lasers: Vaporize tissue (CO2, Er:YAG). Uses: Resurfacing, scars.
• Non-Ablative Lasers: Heat tissue (Nd:YAG, PDL). Uses: Pigment, vascular, hair.

📌 Chromophores: Water (CO2/Er:YAG), Melanin (Alex/Diode/Nd:YAG), Hb (PDL/Nd:YAG).

⭐ Q-switched lasers (e.g., Nd:YAG 1064 nm for black tattoos) produce very short, high-energy pulses, ideal for tattoo removal via photoacoustic effect and treating pigmented lesions.

IPL & Photodynamic Therapy - 💡 Broad Strokes & Activated Agents

⭐ Unlike lasers, Intense Pulsed Light (IPL) emits a broad spectrum of non-coherent light (400-1200 nm), allowing treatment of multiple chromophores simultaneously.

📌 Mnemonic for PDT components: "PAL" - Photosensitizer, Activating light, Local oxygen.

Safety & Complications - 🛡️ Shield & Soothe

• Patient Selection: Crucial. Assess Fitzpatrick skin type; types IV-VI ↑ risk PIH/burns.
  • 
  • Fitzpatrick Skin Types & Risks

    Type	Sun Reaction	Risk Level
    I-II	Always/usually burns	Low
    III	Sometimes burns, tans	Moderate
    IV-VI	Rarely burns, tans easily	High (PIH/burns)

• Protection:
  • Ocular: Mandatory eye shields (patient) & specific eyewear (operator).
  • Skin Cooling (📌 CPP): Pre, parallel, post (contact, cryogen, air) for comfort, ↓ side effects.
• Effects:
  • Common: Erythema, edema, pain, purpura (PDL) - transient.
  • Adverse: Pigmentary changes (PIH in IV-VI), blisters, crusts, scars, infection.
• Care:
  • Pre: Sun avoidance, stop photosensitizers. Antiviral prophylaxis (HSV hx).
  • Post: Sunscreen, gentle care. Topicals if needed.

• ⭐ Test spots vital for Fitzpatrick IV-VI or PIH history to minimize adverse events.

• PIH Management:

High‑Yield Points - ⚡ Biggest Takeaways

• Selective photothermolysis: specific chromophores (melanin, hemoglobin, water) absorb specific laser wavelengths.
• Q-switched lasers (Nd:YAG, Ruby) treat tattoos and pigmented lesions.
• Pulsed Dye Laser (PDL 585/595 nm) targets hemoglobin for vascular lesions.
• Ablative lasers (CO2, Er:YAG) resurface skin by targeting water.
• Intense Pulsed Light (IPL): polychromatic light for various pigment, vascular issues, and hair removal.
• For laser hair removal, Nd:YAG (1064 nm) is safer for darker skin types.