Lasers Med Sci DOI 10.1007/s10103-010-0809-6
REVIEW ARTICLE
Are home-use intense pulsed light (IPL) devices safe? Godfrey Town & Caerwyn Ash
Received: 2 June 2010 / Accepted: 7 June 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 60825-9 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 e-mail:
[email protected]
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
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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 65–70°C causing sufficient damage to the hair follicle to prevent its regrowth.
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/cm2. 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).
Materials and methods
Spectral emission measurement
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
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)
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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.
radiation hazard to the cornea and lens were assessed in accordance with IEC TR 60825-9 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].
Spatial distribution of energy
Measured fluence
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.
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 2.8–4.3 J/cm2, whereas the range of the iPulse Personal was 7–9.98 J/cm2. 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/cm2 to 6.8 J/cm2 (Fig. 2).
Test results
Ocular hazard assessment Spectral distribution 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 Fig. 2 Measured fluence values for all possible settings of the tested devices in this investigation
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.
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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.
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).
Safety features
Ocular hazard assessment
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 60825-9 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 methodology for assessing the Retinal Thermal Hazard and the Blue Light Hazard has been published previously using a similar photospectrometer to the OceanOptics 2000+ [4]. Because of the low cut-off filter (475 nm) and short pulse duration (
