Laser, IPL, and Light-Based Device Treatments
The governing principle
Selective photothermolysis: a wavelength is absorbed by a target chromophore - melanin, hemoglobin, or water - and converted to heat, damaging the target while sparing surrounding tissue if the pulse duration is shorter than the target's thermal relaxation time. Wavelength sets depth and chromophore; fluence (J/cm2) sets energy delivered; pulse duration sets thermal confinement; spot size affects both depth of penetration and scattering. Larger spots deliver more effective fluence at depth.
Intense pulsed light is not a laser. It emits polychromatic, non-coherent, broadband light, usually through filters, and its effects are less selective and harder to predict. Devices are classified by hazard class; operators must know the controlled area, key control, eyewear requirements for both client and operator, and the emergency stop.
Safety practice
Fitzpatrick-appropriate settings, a test spot, skin cooling, clean dry skin, no tan or self-tanner, no photosensitizing medications or recent sun, and eye shields matched to the wavelength. Practitioners must never treat outside licensed scope and must know which devices require medical direction in Washington.
Contraindications and adverse events
Pregnancy, active infection, photosensitivity, recent isotretinoin, tanning, tattooed or freshly waxed skin, and unrealistic expectations. Adverse events include burns, blistering, prolonged erythema, post-inflammatory hyperpigmentation, hypopigmentation, paradoxical hair stimulation, and eye injury.
Traps
- Calling IPL a laser or a laser IPL.
- Choosing the highest fluence to get faster results.
- Treating tanned or recently sun-exposed skin.
- Assuming eye protection is only for the client.
Rule of thumb
Darker skin means more competing melanin, so lower fluence, longer wavelength, longer pulse, and more conservative test spots - and remember that a larger spot size reaches deeper.