Review of Alster TS et. al. Effect of a novel low-energy pulsed-light device for home-use hair removal

June 2, 2009

Dermatol Surg. 2009 Mar;35(3):483-9.

Effect of a novel low-energy pulsed-light device for home-use hair removal

Alster TS, Tanzi EL.

Review copyright 2009

This appears to be the first clinical study of the Silk’n home use intense pulsed light for hair removal.  The authors call this “the beginning of a major trend in laser dermatology.”  Given the nicely performed study, and promising results presented, they may be right.

In this study, hair removal was evaluated in one or more treatment areas of twenty women, while matched control areas were left untreated.  The subjects generally had lighter skin and darker hair, and treated areas included underarms, forearms, legs, and bikini lines.  Hair counts were performed in treatment areas and control areas, using a reliable method of manual hair counts (average of 3 manual counts in a 2cm2 or 3cm2 template).  Follow-up measurements were performed at 3 and 6 months, which is generally accepted as the appropriate time frame to assess permanent hair reduction.

The results were quite impressive – virtually no change in hair counts of the control sites at any time, but significant reductions in hair counts (36% to 53% depending on body location) at six months.

While small, this study was appropriately powered and appropriately controlled, and used objective, quantitative outcome measures.  While it would have been nice if the study included multiple sites to eliminate the potential for site bias, a single site study is reasonable for the early stage of clinical work and small size of the study.  (According to a company press release in March 2008, more than 150 patients were treated at 4 total centers, where the results of this first study were successfully replicated.  AestheticDeviceReview hopes these results are published soon.)

A curious point of this study is the 2-week intervals in the series of 3 treatments in the study.  Typically, laser hair removal is performed with at least 4-week intervals between treatments, to maximize the amount of hair follicles in the anagen phase, which is thought to provide the best results.  Perhaps, in addition to their novel device, this novel application of bi-weekly treatments contributes to the results.  Further study is needed here.

The study’s author, Dr. Alster, purchased stock options in the company subsequent to the study.  Given these results, and the reported results from the expanded data set, we can expect these options to become quite valuable.


Review of Khatri KA et. al. Efficacy and safety of a 0.65 millisecond pulsed portable ND:YAG laser for hair removal.

March 1, 2009


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.



January 29, 2009

Welcome to Aesthetic Device Review, an occasional review of notable articles on aesthetic devices from peer-reviewed publications.