Laser and Light-Based Therapies
What this domain tests
Laser and light items test selective photothermolysis, chromophore targeting, device selection by Fitzpatrick type, safety, and expected endpoints. You do not need to operate a laser, but you must recognize wavelengths, cooling, and when to stop.
Core rules
- Selective photothermolysis requires a wavelength absorbed by the target chromophore, a pulse duration shorter than the target thermal relaxation time, and enough fluence to damage the target while cooling protects the epidermis.
- Melanin absorbs broadly from 400–1100 nm; hemoglobin peaks near 532 and 577 nm; water absorbs strongly above 1200 nm.
- 1064 nm Nd:YAG penetrates deeper and is safer for darker Fitzpatrick types when used with longer pulses and adequate cooling; 755 nm alexandrite and 694 nm ruby are more melanin-sensitive.
- IPL is polychromatic and not a laser; it is used for pigment and vascular concerns with cutoff filters.
- Contraindications include recent tan, photosensitizing medications, pregnancy in many protocols, active infection, and isotretinoin.
Worked example
A Fitzpatrick V client wants hair reduction on the upper lip. The safest choice is 1064 nm Nd:YAG with a longer pulse, lower fluence, and aggressive cooling. The reasoning: melanin in the epidermis competes with the follicle target, so a longer wavelength and cooling reduce epidermal injury and hypopigmentation risk.
Traps
Do not treat tanned skin. Do not skip eye protection. Do not confuse laser with IPL. Stop if the client reports excessive heat or if unexpected whitening occurs.