fractional erbium-doped laser prototype (5 mJ/pulse), with biopsies at 1 hour; 1, 3, 5, and 7 days; and 3 months after treatment.7 Microscopic epidermal necrotic debris containing melanin and thermally damaged keratinocytic debris formed in the subgranular space within 1 day posttreatment and was intracorneal or shed from the epidermis by 7 days posttreatment.7 Formation of new dermal collagen, to replace the thermally damaged collagen, was observed 3 months posttreatment.7 Histologic assessments were consistent with this timeline of pigment migration and epidermal recovery in a study of 18 individuals treated on the forearm with the 1927 nm wavelength handpiece of the NFDL system (5 mJ/pulse; coverage, 5%–10%).8
As mentioned previously, an important advantage of nonablative fractional infrared lasers is that they target water molecules rather than melanin, and this improves safety profiles files for use on Fitzpatrick skin type III–VI (darker skin types).2,9 With the 1440 nm and 1927 nm NFDL system, the 1927 nm wavelength, compared with the 1440 nm wavelength, confers a higher absorption coefficient for water, thus generating wider and shallower MTZs independent of treatment coverage (Table 2; Figure 2).10 Notably, interaction of the 1927 nm wavelength handpiece with the skin leaves the stratum corneum structurally intact, with a zone of subepidermal clefting and thermally altered dermal collagen (Figure 2).10
Fractional Photothermolysis Enhances Skin Permeability
Nonablative fractional photothermolysis thermally damages the epidermis in a pixilated pattern and enables laser-assisted topical drug delivery as an adjunct in the treatment of photoaging. 11,12 Topical uptake experiments (n=3) with the 1440 nm and 1927 nm NFDL system were performed on abdominal skin grafts (500-μm thickness) with an antioxidant serum contain-
