Extended theory of selective photothermolysis: a new recipe for hair cooking?

Unlocking the Power of Light on the Skin: A Comprehensive Review on Photobiomodulation

Photobiomodulation (PBM) is a procedure that uses light to modulate cellular functions and biological processes. Over the past decades, PBM has gained considerable attention for its potential in various medical applications due to its non-invasive nature and minimal side effects. We conducted a narrative review including articles about photobiomodulation, LED light therapy or low-level laser therapy and their applications on dermatology published over the last 6 years, encompassing research studies, clinical trials, and technological developments. This review highlights the mechanisms of action underlying PBM, including the interaction with cellular chromophores and the activation of intracellular signaling pathways. The evidence from clinical trials and experimental studies to evaluate the efficacy of PBM in clinical practice is summarized with a special emphasis on dermatology. Furthermore, advancements in PBM technology, such as novel light sources and treatment protocols, are discussed in the context of optimizing therapeutic outcomes and improving patient care. This narrative review underscores the promising role of PBM as a non-invasive therapeutic approach with broad clinical applicability. Despite the need for further research to develop standard protocols, PBM holds great potential for addressing a wide range of medical conditions and enhancing patient outcomes in modern healthcare practice.

Light-based home-use devices for hair removal: Why do they work and how effective they are?

OBJECTIVES

This review has the following objectives: Firstly, it provides an explanation of the evolution of laser/intense pulsed light (IPL) hair reduction modalities from high fluence professional devices to low fluence home-use appliances. Secondly, it summarises published literature reviews on home-use devices (HUDs) as evidence of their growing credibility. Thirdly, it proposes mechanistic differences in light delivery regimes and the resulting divergences in mode of action.

MATERIALS AND METHODS

An extensive literature search was performed to review the progress of laser/IPL-induced hair reduction and determine what evidence is available to explain the mode of action of professional and HUDs for hair removal. Establishing the likely biological mode of action of professional high-fluence systems versus home-use low-fluence appliances was performed by combining data obtained using ex vivo hair follicle (HF) organ culture and the clinical results involving human participants.

RESULTS

Significant basic science and clinical evidence has been published to confirm the clinical efficacy and technical safety of many laser and IPL home-use devices for hair removal. Clearly, HUDs are different compared to professional systems both in terms of fluence per pulse and in terms of biological mechanisms underlying hair removal. Here we presented data showing that a single low fluence pulse of both 810 nm laser (6.6 J/cm² , 16 ms) and IPL (9 J/cm² , 15 ms and 6.8 J/cm² , 1.9 ms) leads to induction of catagen transition. Catagen transition was characterized by morphological changes similar to what occurs in vivo with occasional detection of apoptosis in the dermal papilla and outer root sheath cells. This suggests that high hair reduction can be expected in vivo and longer-term treatment might result in HF miniaturization due to a cumulative effect on the dermal papilla and outer root sheath cells. In line with this hypothesis, in this review we demonstrate that long-term application of a commercially-available home-use IPL appliance resulted in persistent hair reduction (80%) one year after last treatment. These data are in line with what was previously reported in the literature, where clinical studies with home-use IPL appliances demonstrated high efficacy of hair reduction on female legs, armpits and bikini zones, with full hair regrowth after four treatments following cessation of IPL administration. Limitations of HUDs include lack of hair clearance for very dark skin types and low speed of treatment compared with professional devices. Numerous uncontrolled and controlled clinical efficacy studies and technical safety investigations on consumer-use appliances support many of the leading manufacturers' claims.

ANALYSIS & CONCLUSIONS

Manufacturers make consumer appliances safe and easy to use by considering "human factors," needs and capabilities of a variety of users. Safety is of primary concern to manufacturers, regulators and standards bodies as these appliances may be accessible to children or their use attempted on unsuitable skin types without full awareness of potential side effects. Consumer cosmetic appliances are provided with warnings and obvious safety notices describing the nature of any ocular or dermal hazard and precautions for reducing risk of accidental injury, infection, etc. HUDs employing optical energy are provided with design and engineering controls such as safety switches, alarms and sensors to prevent their incorrect operation or eye exposure. In-vivo studies demonstrated that low fluence home-use hair removal devices can result in high hair reduction efficacy after a short treatment regime, while prolonged and less frequent (once in six weeks) maintenance treatment over a year can lead to high and sustained hair reduction even one year after cessation of treatment. Home-use hair removal devices can be a useful adjunct to professional in-office treatments with high professional awareness. There are sufficient positive arguments for practitioners to make the case to patients for HUDs as "companion" products to professional treatments. In addition, devices for hair removal can be used effectively as stand-alone products by the consumer if they are willing to adopt a regime of regular or frequent use. Further clinical studies involving dynamic observation of HF cycle stage and type (terminal vs. vellus) over the total duration of treatment, for example, using biopsies or non-invasive imaging are necessary to confirm the proposed mode of action of low fluence pulses in a combination with treatment and maintenance regimes. Lasers Surg. Med. 51:481-490, 2019. © 2019 Wiley Periodicals, Inc.

Comparison of Efficacy Between Novel Robot-Assisted Laser Hair Removal and Physician-Directed Hair Removal

OBJECTIVE

This study aimed to evaluate the number of laser irradiation sessions, process duration, and hair removal rate required for robot-assisted automatic versus physician-directed laser hair removal.

BACKGROUND DATA

This research group previously developed and tested an automatic laser hair removal (LHR) system to provide uniform laser treatment distribution.

METHODS

Six subjects 20-40 years of age, with skin types III-IV completed this study. A home-use LHR device with an 810 nm diode laser was used to treat equal-sized areas of both upper thighs; a random computer generator determined the use of a robot-assisted automatic LHR system or physician-directed LHR on the right or left thigh. The treatment schedule comprised five visits; subjects were photographed and shaved, and received LHR during the first through the fourth visits at 2-week intervals. The fifth visit occurred 1 month after the fourth, and only involved photography.

RESULTS

All subjects successfully completed the clinical trial with no noticeable or permanent side effects. The average hair removal rates were 49.0% (standard error of the mean [SEM]: 4.0) and 29.5% (SEM: 4.0) for robot-assisted and physician-directed LHR, respectively. The average treatment duration and number of irradiation shots were 18 min, 30 sec (SEM: 33 sec) and 260 (SEM: 5.7) for robot-assisted LHR and 3 min, 11 sec (SEM: 15 sec) and 73 (SEM: 5.9) for physician-directed LHR.

CONCLUSIONS

This clinical study successfully demonstrated the safety and effectiveness of robot-assisted LHR. The proposed novel system will benefit both patients and clinicians.

Efficacy of long‐ and short pulse alexandrite lasers compared with an intense pulsed light source for epilation: a study on 532 sites in 389 patients

BACKGROUND

Undesirable hair growth presents a significant problem for many patients, and photoepilation has become a very popular procedure in aesthetic and cosmetic practice. Among the systems used are the long- and short-pulsed alexandrite lasers (LP-Alex, SP-Alex) and intense pulsed light (IPL) sources. The present study retrospectively examined the outcome of these systems from the viewpoint of efficacy and side effects.

PATIENTS AND METHODS

Three hundred and eighty-nine patients (370 females and 19 males, mean age 36.4 yrs, skin types II-V) were admitted to the study, with a total of 532 treated sites. They were treated either with the LP-Alex, SP-Alex or IPL. Subjective evaluation and interview of the patients was held prior to every treatment session. Six to eight treatments were required with the alexandrite lasers, 2.4-2.8 months between treatments, and the IPL source required 8-9 treatments, 2-2.5 months apart.

RESULTS

No significant difference was seen between the LP- and SP-Alex, or between both of them and the IPL source, although the period to regrowth was longer for the lasers. Erythema and oedema were more noticeable with the LP-Alex, as were crusting and hyper- and hypopigmentation. Discomfort was greatest with the LP-Alex and the IPL source. Hair induction at the borders of the treated area on the face and neck was seen only with the LP-Alex, and correlated statistically significantly with any episode of severe erythema, crusting or hyperpigmentation.

CONCLUSIONS

There was no statistically significant difference between the LP-, SP-Alex and IPL photoepilation with regard to efficacy. Transient side effects were highest with the LP-Alex, and least with the IPL system. In the LP-Alex treated face and neck sites, 3.1% had hair induction in the borders of the treated areas.

A multicentre trial of the epilation efficacy of a new, large spot size, constant spectrum emission IPL device

This study assesses the efficacy of a new, low fluence, constant spectrum IPL device. In three European centres, 52 females underwent epilation of one arm axilla with the new IPL, the contralateral axilla serving as a treatment control. Satisfied patients at the 1-month assessment received no further treatments and in the other patients up to five further monthly sessions were given. Clinical photography was taken at the pretreatment baseline and at approximately 1 month later. Side effects and hair attributes were graded. Patient satisfaction was graded. All patients completed the study: 11 required one treatment, with eight, 13, 11 and nine requiring two, three, four and five sessions, respectively. Side effects were minimal. A total of 44 patients were very satisfied with the final result, eight were somewhat satisfied and no patient expressed dissatisfaction, giving an overall satisfaction score of 84.6%. In all cases, hair regrowth in the treated side was finer and lighter. The greatest efficacy was seen in coarse dark hair in darker skin, and least efficacy was noted in fine blonde hair in lighter skin. Epilation with this constant spectrum IPL was safe, effective, well tolerated, and with high patient satisfaction. Repeated sessions were required in some patients with lighter hair and skin.

Eflornithine cream combined with laser therapy in the management of unwanted facial hair growth in women: a randomized trial

BACKGROUND

Eflornithine cream is approved for the reduction of unwanted facial hair in women. The mechanism of action for eflornithine is reduction in follicular cell growth rate, while laser photoepilation heats hair and adjacent tissues to suspend growth.

OBJECTIVE

The objective was to assess the efficacy and safety of eflornithine or vehicle with laser therapy in the treatment of unwanted facial hair in women.

METHODS

Subjects were randomized to treatment with eflornithine on one side of the face and vehicle on the contralateral side for 34 weeks. Subjects received Nd:YAG or alexandrite laser therapy to both sides of the face at Weeks 2 and 10. Blinded evaluations included left to right comparisons and appearance relative to baseline.

RESULTS

Fifty-four women completed the trial. From Weeks 6 through 22, eflornithine-treated sides showed significant reduction in hair growth. By Week 34, no significant differences were seen. Subject grading showed significant and persistent hair reduction through Week 34 for eflornithine-treated sides. The safety profile for combination therapy is similar to eflornithine alone.

CONCLUSION

Eflornithine is safely used in conjunction with laser hair removal treatments and promotes more rapid hair removal when combined with laser treatment. Patients demonstrate a clear preference for treatment with laser and eflornithine.

A Pilot Study to Optimize Laser-Assisted Hair Removal Using Real-Time High-Speed Infrared Imaging

OBJECTIVE

The aim of this study was to investigate thermal effects on the skin surface during laser-assisted hair removal using real-time high-speed infrared imaging.

BACKGROUND DATA

Although hair laser removal (HLR) can be considered an inherently safe treatment, there may be approaches to optimise the benefit/risk ratio of this common therapeutic and cosmetic procedure.

METHODS

In this pilot study on three subjects, a ruby laser equipped with a cryogen spray cooling (CSC) system was used to investigate the effect of different CSC durations and delay times between CSC and the laser impulse. Skin surface temperature (SST) was assessed in real-time using a high-speed infrared camera (ThermaCam Phoenix) and a special image analysis software (analySIS Doku).

RESULTS

There was no substantial difference of SST between the use of CSC spurts of 10 and 20 msec (6.1 degrees C versus 5.7 degrees C). The use of single laser and cooling parameters revealed baseline SST of 31.7 degrees C, immediately after CSC (10 ms) SST of 6.5 degrees C, and after laser pulse SST of 47 degrees C. Using fluences of 10-20 J/cm(2), a marked difference in temperature was observed between the skin surface and hair (e.g., 26.7 degrees C versus 57.5 degrees C). SST of 62-64 degrees C was observed using fluences of 18-20 J/cm(2), resulting in adverse effects. A maximum SST of 59 degrees C was observed using a CSC spurt of 40 msec, whereas a maximum SST of 60 degrees C was recorded for 30, 20, and 10 msec. The use of CSC delay time of 600 msec revealed baseline SST of 34.6 degrees C, immediately after CSC (10 msec) SST of 5.2 degrees C, after 600 msec delay SST of 21.5 degrees C, and SST of 60 degrees C following the laser pulse. By contrast, 100 msec delay time revealed baseline SST of 34.8 degrees C, immediately after CSC (10 ms) SST of 7 degrees C, after 100 msec delay SST of 7.5 degrees C, and SST of 55.2 degrees C following the laser pulse.

CONCLUSION

Our preliminary data indicate that side effects of HLR can be avoided using CSC duration of 10 msec with a delay of about 200 msec. Short delay times between the CSC and laser pulse seem to result in lower post-irradiation SST and may therefore lead to less adverse effects. With regard to the fluence used in HLR, it is of importance that the maximum SST remains below 60 degrees C. Based on these preliminary results, real-time high-speed infrared imaging seems to be an interesting method to study the thermodynamics on skin surface during laser treatment.

Selektive Retinatherapie

Selective retina therapy (SRT) is currently under evaluation, as a new and very subtle laser method, for the treatment of retinal disorders associated with a degradation of the retinal pigmentary epithelium (RPE). SRT makes it possible to selectively effect the RPE, sparing the adjacent neural retina with the photoreceptors and also the choroid below the RPE. In the best case, the therapy leads to regeneration of the RPE and a long-term metabolic increase at the chorio-retinal junction. In contrast to conventional laser photocoagulation, which is associated with complete thermal necrosis of and around the treated site, absolutely no scotoma occurs in SRT. This paper reviews the methods and mechanisms behind the selective effects of the RPE. In vitro and preclinical results are used to describe the bandwidth of selective effects with respect to different irradiation settings. An optoacoustic technique is introduced to visualize effects that cannot be seen by ophthalmoscopy and to facilitate dosimetry control without recourse to angiography completes the report.