Are home-use intense pulsed light (IPL) devices safe?

Transcription

1 Lasers Med Sci (2010) 25: DOI /s REVIEW ARTICLE Are home-use intense pulsed light (IPL) devices safe? Godfrey Town & Caerwyn Ash Received: 2 June 2010 /Accepted: 7 June 2010 /Published online: 13 July 2010 # Springer-Verlag London Ltd 2010 Abstract The domestic market for home-use hair removal devices is rapidly expanding and there are numerous intense pulsed light (IPL) products now available globally to consumers. Technological challenges for the design of such devices include the need to be cost-effective in mass production, easy to use without training, and most importantly, clinically effective while being eye-safe. However inexpensively these light-based systems are produced, they are designed to cause biological damage to follicular structures, so precautions to prevent both ocular and epidermal damage must be considered. At present, there are no dedicated international standards for IPL devices. This review directly compares three leading domestic IPL hair removal devices: ipulse Personal (CyDen, UK), Silk'n/SensEpil (Home Skinovations, Israel), and SatinLux/Lumea (Philips, Netherlands) for fluence, emitted wavelength spectrum, time-resolved footprint, and spatial distribution of energy. Although each device has a primary mechanical or electrical safety feature to ensure occlusion of the output aperture on the skin to prevent accidental eye exposure, the ocular hazard of each device has been measured to IEC TR standard using an G. Town Swansea Metropolitan University, Swansea SA1 6ED, UK C. Ash School of Medicine, Swansea University, SA2 8PP Swansea, UK G. Town (*) 88 Noah s Ark Lane, Lindfield, West Sussex RH16 2LT, UK godfreytown@mac.com Ocean Optics HR2000+ photo spectrometer for both potential corneal and retinal damage. Using established measurement methods, this review has shown that the measured output parameters were significantly different for the three systems. Using equipment traceable to national standards, one device was judged at its two highest settings to be hazardous for naked eye viewing. This investigation also reports on the significantly different pulse durations of the devices measured and considers the potential impact on safety and efficacy in the light of the theory of selective photothermolysis. Although these devices offer low-cost personal convenience of treatment in the privacy of the home, ocular safety may be inadequate in the event of primary safety mechanism failure. Keywords Domestic hair removal. Optical hazard. Spectral output. Square pulse. Spectral footprint Introduction The hair-removal industry is reportedly worth approximately 10 billion US dollars annually and many companies are expected to launch new light-based devices for hair reduction within the next year following those who have already done so. Over the past decade, several companies have been exploring simple low-energy home-use devices and such systems are usually limited to a few energy settings, fixed pulse duration, single fixed filter, small treatment areas without any option for parallel skin cooling and covering fewer skin tones compared to professional systems. Technological challenges for such devices are that they have to be clinically effective while being eye-safe, easy to use without training, and most importantly for the manufacturer, cost-effective in mass production. Such

2 774 Lasers Med Sci (2010) 25: devices can offer greater privacy and personal convenience to the consumer than professionally delivered hair-removal treatments and a reduction in cost of maintaining hair-free skin for extended periods. There is a market for a convenient and effective method of long-lasting epilation using light with a number of FMCG corporations looking to enter this new sector. Nevertheless, however inexpensively these light-based systems are produced, they are designed to cause biological damage to follicular structures and precautions must be taken to prevent epidermal and ocular damage. A consumer IPL hair-removal system operates on the same principle of selective photothermolysis as professional IPL/laser systems. The optical energy of suitable wavelengths is emitted and absorbed by melanin and other chromophores in the user s skin within a time constant that heats the actively growing hair shaft and hair bulb to temperatures of C causing sufficient damage to the hair follicle to prevent its regrowth. Materials and methods The measurement methods used in this investigation are those reported in previously published studies by Town and Ash et al. on the measurement of professional and homeuse IPL systems [1 3]. The devices evaluated in this report include: ipulse Personal (CyDen Ltd, Swansea, UK), Silk n/sensepil (Home Skinovations Ltd, Yokneam, Israel), and SatinLux/Lumea (Philips, Eindhoven, Netherlands). All devices were purchased through major retailers to reflect product quality and performance being delivered to consumers. The Home Skinovations brands Silk n and SensEpil were found to be the same, and the Philips brands SatinLux and Lumea were also found to be the same in respect of all measurements made (Fig. 1). Radiant exposure (fluence) measurement Fluence is the amount of light energy delivered per unit area and is measured in J/cm 2. As energy is absorbed, the temperature of the intended chromophore increases and undergoes biological changes. The ideal radiant exposure will raise the temperature of the chromophore to a level that causes damage to the target but does not produce collateral damage, such as burns or blisters, to adjacent tissue. Excessive fluence may cause side-effects while too low energy may result in under-treatment and user dissatisfaction. The fluence measurements were produced using an energy meter and absorber head (Ophir LaserStar Power Energy Monitor, Ophir L40-150, A-DB-SH-NS Absorber Head: Ophir Optronics Ltd, Jerusalem, Israel). Spectral emission measurement The primary chromophores in the skin, which are key to most IPL/laser treatments, have unique absorption spectra. This means that depending on the treatment target, specific wavelengths will be more effective in treating certain conditions than others. The range of wavelengths used should therefore take into account the absorption spectra of all chromophores because heating a non-target chromophore can damage adjacent tissue. Knowledge of the spectral output also provides information on any unwanted wavelengths, such as ultraviolet and infrared radiation, Fig. 1 From left to right, ipulse Personal (CyDen Ltd., UK), Silk n/sensepil (Home Skinovations, Israel), SatinLux/Lumea (Philips, The Netherlands)

3 Lasers Med Sci (2010) 25: which can present immediate and/or long-term tissue injury risks. Time-resolved spectral measurements confirm the biologically effective pulse duration of an IPL, during which the desired wavelengths are delivered in the optimum intensity. The time-resolved spectra were produced using an HR2000+ spectrometer (Ocean Optics, Dunedin, FL, USA) and its counterpart Spectra Suite software, which facilitates 3-D visualization of the pulse structure by time and wavelength distribution. Spatial distribution of energy Uniform distribution of energy delivered across a treatment area on tissue is clearly important to avoid either hotspots or areas of under-treatment. Accurate, reproducible, and objective data on spatial distribution of optical energy is difficult to achieve. For the purposes of this investigation, it was considered adequate to record energy distribution patterns on laser alignment paper (Zap-It Corp., Salisbury, NH, USA) and analyze them using custom software to produce assessable histograms to determine the approximate energy distribution pattern. Ocular hazard assessment Ocular safety is one of the highest safety concerns for a lightemitting device. This assessment was made with an HR2000+ photospectrometer with cosine correction in terms of spectral irradiance (Wm 2 nm 1 ) and calibrated and traceable to national standards. Pulse duration was determined by full width half maximum (FWHM) measurement of the spectral data. The results from these measurements were used to assess the optical radiation hazard to the human eye. Retinal thermal hazard (RTH), blue light hazard (BLH), and infrared radiation hazard to the cornea and lens were assessed in accordance with IEC TR and the International Committee on Non-Ionizing Radiation Protection (ICNIRP) Guidelines on Limits of Exposure to Broad-band Incoherent Optical Radiation, as there are no specific international IPL standards [4]. Test results Measured fluence This investigation is focused on actual measured rather than claimed fluence values using previously published methodology traceable to national standards [2]. Extremes of measured fluence ranges were seen where the Silk n/ SensEpil was found to be J/cm 2, whereas the range of the ipulse Personal was J/cm 2. Each device has a range of output fluences designed to prevent excessive epidermal absorption by pigmented Fitzpatrick skin types. The Philips SatinLux/Lumea device produced measured fluences across all available settings from 2.5 J/cm 2 to 6.8 J/cm 2 (Fig. 2). Spectral distribution The ipulse Personal is intended to treat Fitzpatrick skin type s I IV with a 530-nm filter, the Silk n/sensepil to treat skin types I IV with a 475-nm filter and the SatinLux/ Lumea skin types I V with a 575-nm absorption filter. The three filters are designed to remove unwanted ultraviolet wavelengths from emitted output by either an absorption or reflectance filter used to attenuate lower wavelengths from reaching the epidermis. Fig. 2 Measured fluence values for all possible settings of the tested devices in this investigation

4 776 Lasers Med Sci (2010) 25: The spectral distribution of the Silk n/sensepil shows a typical filtered broadband Xenon flashlamp emission with 10.17% of optical energy under 500 nm, thereby significantly increasing epidermal absorption. The SatinLux/ Lumea device produces pulses of light to stimulate the hair follicle into the resting (catagen) phase, resulting in shedding of the hair shaft and inhibition of hair regrowth [9]. This device treats the widest range of Fitzpatrick skin types (I V) and also has the highest cut-off filter position (575 nm) (Fig. 3). Time-resolved spectral analysis The Silk n/sensepil and SatinLux/Lumea utilize free discharge technology to deliver energy to the flashlamp, and as a result, the pulse duration is a short peak of high intensity determined by the time it takes for the capacitor to discharge (Fig. 4). The time-resolved spectral footprint of the ipulse Personal shows the device emitting a nearly even distribution of energy over 25 to 60-ms pulse durations, which are within widely recognized TRT durations for successful hair removal. Safety features The safety of a home-use device is a major consideration for the consumer and of considerable importance to consumer safety agencies. In the absence of an internationally recognized standard for intense light sources, manufacturers of home-use IPL devices should test to the international technical report IEC TR to calculate the retinal thermal hazard in the event of failure of contact sensors or safety pressure switches designed to prevent accidental emission of optical radiation [4]. The Home Skinovations Silk n/sensepil, will only discharge when a switch makes contact when the handpiece is pressed against the user s skin and a trigger button on the rear of the handpiece is depressed simultaneously. The Home Skinovations latest SensEpil model uses a built-in skin color detector to prevent use on darker skin types. As a precaution against accidental treatment at higher than the recommended energy, this device is programmed with the fluence limited to only use the lowest of five energy settings for the first 50 shots. From 50 to 150 shots, the only energy settings that can be selected are the lowest three levels. After the 150th shot, the device is fully operational. These pre-sets appear to be employed so that the user will feel more comfortable having used the device at lower levels without experiencing any adverse reactions. The ipulse Personal uses a skin-sensitive electrical conductance safety system comprising four contact pins, which must all be in contact with coupling gel and skin for the device to activate. The use of coupling gel with the ipulse Personal is mandated in the product insert. The Philips SatinLux/Lumea has four push switches, which must all be depressed to activate the device on skin (Fig. 5). Ocular hazard assessment The methodology for assessing the Retinal Thermal Hazard and the Blue Light Hazard has been published previously using a similar photospectrometer to the OceanOptics [4]. Because of the low cut-off filter (475 nm) and short pulse duration (<5 ms), the highest settings [gradient positions 4, 5], the Silk n/sensepil may pose a retinal thermal hazard risk in the event of failure or misuse of the safety switch or accidental emission of light from the edge of the aperture during use. Fig. 3 Spectral distribution of the three measured devices all have different cut-off filters from 475 to 575 nm

5 Lasers Med Sci (2010) 25: Fig. 4 Large difference (graphically) in temporal spectral footprint of the ipulse Personal versus the Silk n/sensepil and the SatinLux/Lumea. Examples shown are of devices at maximum fluence The SatinLux / Lumea and ipulse Personal were both found not to be a risk in the event of failure or intentional misuse of the safety switch or accidental emission of light from the edge of the aperture during use (Fig. 6). Spatial profile Spatial distribution of energy from an IPL system is generally an overlooked parameter [2]. The three devices were discharged onto thermal laser alignment paper (Zap-It Corp, Salisbury, NH, USA) and scanned into custom software to analyze with histograms the distribution of thermal energy across the treatment area. A lack of uniformity could potentially explain side-effects such as hyperpigmentation, hypopigmentation, ineffective treatment or paradoxical hypertricosis. The histogram results show that the ipulse has the most uniform distribution across its 3 cm 2 treatment area (0.09 SD). The SatinLux/Lumea has a greater energy distribution lengthways across the center of its 1 3 cm (3 cm 2 )treatment area compared to the ipulse (0.21 SD). The Silk n/sensepil has a greater distribution with a 0.45 SD increase of energy in the center of its 6-cm 2 treatment window and a perimeter band of minimal energy. Mulholland [5] recommended Fig. 5 Safety systems used by the examined systems: the electrical conductance safety system of the ipulse Personal and the mechanical push switches of the Silk n/sensepil and SatinLux/ Lumea

6 778 Lasers Med Sci (2010) 25: Fig. 6 Comparison of the measured weighted radiance (W m 2 nm 1 ) against the exposure limit value for each setting of the examined devices overlapping the treatment areas of this device by 20% in each direction in his clinical assessment of the Silk n/sensepil (Fig. 7). Discussion The progression of professional hair removal from the clinic or beauty center into the home brings with it the risk of injury to the skin and eyes of consumers. In clinics and salons, such risks are reduced by sufficient training, support, and advice from experienced professionals and the availability of appropriate prescription medication. Evaluation of the safety mechanisms employed by homeuse devices shows that they are not complex and the simple mechanical switches are sufficient to ensure that the device is in good contact with the skin, thus reducing the risk of eye exposure, misuse, or accidental injury. All systems tested are attractively packaged with clear educational material for the customer regarding contraindications to treatment such as too dark skin types, active suntan and medications. However, what cannot be so easily accommodated is the inappropriate purchase and use of such devices by darker skin types than those advised by the manufacturer. There is also scope for misjudgment of skin tone when selecting output settings and consequential unpleasant skin reactions caused by excessive fluence for that skin type or alternatively under-treatment, resulting in poor efficacy in reducing hair and consequent disappointment for the consumer. Attempts have been made by some manufacturers, particularly in the USA, to address these problems such as shipping units to customers who are then required to obtain an activation code from the manufacturer before the device can be used. This gives the manufacturer the chance to attempt to check that the user is of the correct skin tone to use the device. The US FDA has also taken a lead by initially restricting the sale of at least one home-use light-based hair removal device under a 510(k) marketing clearance to be use only under the direction of a physician, after training by a healthcare professional (Silk n, Home Skinovations Ltd, Israel). Moreover, future devices may Fig. 7 Left to right: spatial profile of Silk n/sensepil, SatinLux/ Lumea, and ipulse with corresponding histograms produced from custom software

7 Lasers Med Sci (2010) 25: have to be equipped with skin-sensor technology to ensure that they cannot be used on unsuitable dark skin types or on tanned or inappropriate pigmented skin areas. In the absence of any recognized international standard, the International Electrotechnical Commission report (IEC TR ) should be used by manufacturers to calculate eye hazard of IPL devices in the event of failure of contact or failure of safety pressure switches designed to prevent emission of optical radiation. All manufacturers of such home-use devices should consider testing self-use products against this standard and ensure that the weighted radiance values are less that the exposure limit values for corneal and retinal thermal hazard. Previously, the acknowledged fluence threshold for permanent hair reduction was 5 J/cm 2 required to damage hair follicles sufficiently in-situ to prevent hair regrowth [9]. Measured energy settings of both Silk n/sensepil and SatinLux/Lumea are less than 5 J/cm 2, thus with the lower fluence, only slight damage to the follicle might merely result in temporary hair growth delay by moving the hair into the transitional Catagen (shedding) or Telogen (resting) phase [10]. The arrival of trusted brands of home-use hair-removal laser and IPL devices in the marketplace from multinational FMCG companies may expand public awareness and acceptance of aesthetic light-based technologies and simultaneously lead to an increase in demand for professionally delivered therapy rather than to a decline in demand for clinic-based treatments. It is acknowledged that only one of each device was measured for this study and inherent device tolerances for mass production are unknown. Conclusions For optimum hair reduction, the user should choose a device that delivers sufficient energy within each pulse or pulse train that is within the thermal relaxation time (TRT) of the average terminal hair follicle (20 60 ms) and that is adequate to irreversibly damage the hair follicle or at least prevent any regrowth for an extended period. The ability to vary the energy density will better allow users of different Fitzpatrick skin types control and flexibility of treatment. The designers of the devices measured in this study have had to compromise product performance by reducing manufacturing costs. Inefficiency of a home-use device may well cause frustration and dissatisfaction to the user, due to extended treatment times and greater frequency of use. Additional safety measures are needed to ensure that home-use hair-removal devices are not used on suntanned skin and that treatment is restricted to the appropriate skin tone. There is an urgent need for early ratification of the draft international IEC intense light standard, which encompasses manufacturing standards for both professional and home-use hair removal devices. Meanwhile, home-use IPL devices should be tested to IEC TR and the International Committee on Non-Ionizing Radiation Protection (ICNIRP) Guidelines on Limits of Exposure to Broad-band Incoherent Optical Radiation to ensure eye safety. This study shows that even low-fluence IPL systems can be a risk factor to safe ocular viewing if near ultraviolet emission (i.e., <500 nm) is considerable. There are several clinical efficacy studies reporting significant hair reduction with light-based home-use devices [5 8] but they are carefully structured and monitored and may not reflect the actual complication rate when consumers are using the device outside of a clinical trial. Although studies published to date on home-use devices have not shown paradoxical hair growth or leukotrichia at low fluences, further work is required to understand such side-effects. Numerous concerns exist with bringing this technology to market and manufacturers may be making substantial efforts to address them. For example, the manufacturer of the TRIA (Spectragenics Inc, Pleasanton, USA) has a program to ensure their TRIA home-use laser hair removal device is used only on skin types I IV, including a skin tone chart on the box, a requirement of phone-activation where purchasers must answer questions about their skin type to receive an activation code and a pigment detection meter that comes with the TRIA device. These steps should greatly reduce the risks associated with tanned or slightly darker skin for any user who is seeking to use the device appropriately. Most companies already have or are developing sensors to ensure contact with skin before discharge of optical energy. Although not infallible, they will prevent individuals who are using the device properly, on approved locations of the body, from accidental harmful exposures. It is not possible to prevent wrongful discharge by users who intentionally defeat safeguards. Disclosures Caerwyn Ash is a PhD Graduate at the University of Wales and receives travel grants from the university. He also receives a salary from Cyden Ltd., Swansea, SA1 8PH, UK and has a minor stock-holding in the company. Godfrey Town is a PhD student at the University of Wales and receives consultancy fees and travel grants from CyDen Ltd., Swansea, SA1 8PH, UK and Unilever, Trumball, CT, USA. References 1. Town G, Ash C, Eadie E, Mosley H (2007) Measuring key parameters of intense pulsed light (IPL) devices. J Cosmet Laser Ther 9(3):

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