Cosmetic and Laser Dermatology, Skin Ageing and Photodermatology
Light and skin type
Fitzpatrick phototypes I–VI predict burning and pigmentary response and guide laser settings, peel choice and sun advice. UVB (290–320 nm) causes sunburn and DNA damage; UVA (320–400 nm) drives photoageing and many photodermatoses.
Laser physics
Selective photothermolysis: match wavelength to chromophore (oxyhaemoglobin, melanin, water) and pulse duration to thermal relaxation time. Pulsed dye laser (595 nm) for port-wine stains and erythema; Q-switched lasers for pigment and tattoos; fractional ablative (CO2, erbium) and non-ablative devices for resurfacing; intense pulsed light is broadband light, not strictly a laser.
Complications
Post-inflammatory hyperpigmentation and hypopigmentation are commoner in Fitzpatrick IV–VI; consent, test spots and conservative fluences reduce risk. Burns, scarring and ocular injury are preventable with eye protection and correct cooling.
Cosmetic procedures and photoprotection
Hyaluronic acid fillers, botulinum toxin and chemical peels (superficial salicylic acid, medium TCA) have predictable risks: vascular occlusion with fillers, ptosis with toxin, scarring with deep peels. Sunscreens: SPF mainly reflects UVB while PPD or UVA-PF reflects UVA; apply about 2 mg/cm² and reapply.
Photodermatoses
Polymorphic light eruption (delayed itchy papules on exposed sites), solar urticaria (immediate), drug-induced photosensitivity (thiazides, tetracyclines, amiodarone) and porphyria cutanea tarda (fragile blisters, hypertrichosis, urinary porphyrins).
Traps
- Treating melasma with high-fluence laser.
- Assuming a high SPF alone guarantees UVA protection.
- Missing a photosensitising drug or porphyria in a blistering sun-exposed rash.
Rule of thumb
Darker skin needs lower fluences, longer wavelengths and vigorous cooling - plan for pigment risk, not just the target chromophore.