J Cosmet Laser Ther. 2009 Feb 6:1-6
Efficacy and safety of a 0.65 millisecond pulsed portable ND:YAG laser for hair removal.
Khatri KA, Lee RA, Goldberg LJ, Khatri B, Garcia V.
Skin & Laser Surgery Center of New England, MA and Nashua, NH, USA.
In this 6 patient study, Khatri et. al. evaluate the AeroLase portable Nd:YAG laser for laser hair removal (LHR). While the results appear promising, the conclusion that this device is “as effective and safe as other devices for LHR” is simply not supported. The main study flaws include a very small number of patients treated, poorly performed hair counts, and a complete lack of statistical analysis. The authors even neglected to report the variances around mean hair count reductions.
A strength of the study is the use of an internal control site, as half the axilla was treated and half was untreated. The treated half (either upper or lower) was alternated among consecutive patients. Two treatment regimes (high and low fluence) were studied, one on the left side and one on the right, again alternated among patients. In both cases, randomization would normally be preferred to alternation; however, randomization in such a small number of patients might have resulted in unequal groups. The treatment protocol consisted of a series of four monthly treatments, followed by a one-month and four-month follow up visits. A single, presumably unblinded, individual counted hairs in treated and control sites, pre-treatment and at both follow-up visits.
At the four month follow up, which is a meaningful period for evaluation of permanent hair reduction, the study showed mean reductions in hair counts at both the treated sites (76%) and the control sites (36%). The authors attribute the reduction at the control sites to “diffusion of energy from the treatment side to the control side.” In most other studies, a standard (e.g. 1cm2) area within each of the control and treatment sites is chosen for the hair count, with sufficient spacing to eliminate any potential energy diffusion. In this study, unfortunately, the authors do not disclose how the hair counts were performed, or how the same areas were counted at each of the time points in the study. Therefore, it is difficult to compare these results to other studies. Further, the authors do not describe the variance around the mean hair reductions, or the number of patients who achieved greater hair reduction at the treated site than at the control site. Consequently, it cannot be determined whether the different results in the treated and control sites are statistically significant.
The six patients self-reported satisfaction, resulting in 1 patient dissatisfied, 2 patients satisfied and 3 very satisfied. Patient satisfaction is often unrelated to clinical outcomes, as patients may be satisfied that they particpated in a treatment, even if no objective improvement was measured. So, satisfaction data must be taken with a grain of salt. The patients were not asked to evaluate improvement of treated sites versus control sites, which might have provided more meaningful data.
Unsurprisingly, histology from treatment site biopsies showed qualitiative changes similar to those described in other articles about light-based hair removal devices. No conclusions of effectiveness could be drawn however, as quantitative histological analysis was precluded by the limited sample size (two patients) and lack of biopsies of control sites.
Contrary to the authors’ conclusions, for a given number of treatments, the Aerolase device is not likely to achieve comparable results to a higher fluence, larger spot laser with integrated skin cooling. Skin cooling clearly increases the margin between an effective treatment fluence and over-treatment, higher fluences clearly increase the effectiveness of hair reduction, and larger spot sizes (10mm or greater radius) increase the depth of optical penetration, further enhancing results.
Nevertheless, to provide effective results, the Aerolase may simply require more treatment sessions than the higher-fluence, integrated cooling devices. A significantly larger study, with improved hair-count measurement methods, is required to fully elucidate the capabilities of this device.