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 removaldevices is rapidly expanding and there are numerousintense pulsed light (IPL) products now available globallyto consumers. Technological challenges for the design ofsuch devices include the need to be cost-effective in massproduction, easy to use without training, and mostimportantly, clinically effective while being eye-safe.However inexpensively these light-based systems areproduced, they are designed to cause biological damage tofollicular structures, so precautions to prevent both ocularand epidermal damage must be considered. At present,there are no dedicated international standards for IPLdevices. This review directly compares three leadingdomestic 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, andspatial distribution of energy. Although each device has aprimary mechanical or electrical safety feature to ensureocclusion of the output aperture on the skin to preventaccidental eye exposure, the ocular hazard of each devicehas been measured to IEC TR 60825-9 standard using an

Ocean Optics HR2000+ photo spectrometer for bothpotential corneal and retinal damage. Using establishedmeasurement methods, this review has shown that themeasured output parameters were significantly different forthe three systems. Using equipment traceable to nationalstandards, one device was judged at its two highest settingsto be hazardous for naked eye viewing. This investigationalso reports on the significantly different pulse durations ofthe devices measured and considers the potential impact onsafety and efficacy in the light of the theory of selectivephotothermolysis. Although these devices offer low-costpersonal convenience of treatment in the privacy of thehome, ocular safety may be inadequate in the event ofprimary safety mechanism failure.

Keywords Domestic hair removal . Optical hazard .

Spectral output . Square pulse . Spectral footprint

Introduction

The hair-removal industry is reportedly worth approximate-ly 10 billion US dollars annually and many companies areexpected to launch new light-based devices for hairreduction within the next year following those who havealready done so. Over the past decade, several companieshave been exploring simple low-energy home-use devicesand such systems are usually limited to a few energysettings, fixed pulse duration, single fixed filter, smalltreatment areas without any option for parallel skin coolingand covering fewer skin tones compared to professionalsystems. Technological challenges for such devices are thatthey have to be clinically effective while being eye-safe,easy to use without training, and most importantly for themanufacturer, cost-effective in mass production. Such

G. TownSwansea Metropolitan University,Swansea SA1 6ED, UK

C. AshSchool of Medicine, Swansea University,SA2 8PP Swansea, UK

G. Town (*)88 Noah’s Ark Lane,Lindfield, West Sussex RH16 2LT, UKe-mail: godfreytown@mac.com

Lasers Med SciDOI 10.1007/s10103-010-0809-6

devices can offer greater privacy and personal convenienceto the consumer than professionally delivered hair-removaltreatments and a reduction in cost of maintaining hair-freeskin for extended periods.

There is a market for a convenient and effective methodof long-lasting epilation using light with a number of FMCGcorporations looking to enter this new sector. Nevertheless,however inexpensively these light-based systems are pro-duced, they are designed to cause biological damage tofollicular structures and precautions must be taken to preventepidermal and ocular damage. A consumer IPL hair-removalsystem operates on the same principle of selective photo-thermolysis as professional IPL/laser systems. The opticalenergy of suitable wavelengths is emitted and absorbed bymelanin and other chromophores in the user’s skin within atime constant that heats the actively growing hair shaft andhair bulb to temperatures of 65–70°C causing sufficientdamage to the hair follicle to prevent its regrowth.

Materials and methods

The measurement methods used in this investigation arethose reported in previously published studies by Town andAsh et al. on the measurement of professional and home-use IPL systems [1–3]. The devices evaluated in this reportinclude: iPulse Personal (CyDen Ltd, Swansea, UK),Silk’n/SensEpil (Home Skinovations Ltd, Yokneam, Israel),and SatinLux/Lumea (Philips, Eindhoven, Netherlands). Alldevices were purchased through major retailers to reflectproduct quality and performance being delivered toconsumers. The Home Skinovations brands Silk’n and

SensEpil were found to be the same, and the Philips brandsSatinLux and Lumea were also found to be the same inrespect of all measurements made (Fig. 1).

Radiant exposure (fluence) measurement

Fluence is the amount of light energy delivered per unitarea and is measured in J/cm2. As energy is absorbed, thetemperature of the intended chromophore increases andundergoes biological changes. The ideal radiant exposurewill raise the temperature of the chromophore to a level thatcauses damage to the target but does not produce collateraldamage, such as burns or blisters, to adjacent tissue.Excessive fluence may cause side-effects while too lowenergy may result in under-treatment and user dissatisfac-tion. The fluence measurements were produced using anenergy meter and absorber head (Ophir LaserStar PowerEnergy Monitor, Ophir L40-150, A-DB-SH-NS AbsorberHead: Ophir Optronics Ltd, Jerusalem, Israel).

Spectral emission measurement

The primary chromophores in the skin, which are key tomost IPL/laser treatments, have unique absorption spectra.This means that depending on the treatment target, specificwavelengths will be more effective in treating certainconditions than others. The range of wavelengths usedshould therefore take into account the absorption spectra ofall chromophores because heating a non-target chromo-phore can damage adjacent tissue. Knowledge of thespectral output also provides information on any unwantedwavelengths, such as ultraviolet and infrared radiation,

Fig. 1 From left to right, iPulsePersonal (CyDen Ltd., UK),Silk’n/SensEpil (HomeSkinovations, Israel),SatinLux/Lumea(Philips, The Netherlands)

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which can present immediate and/or long-term tissue injuryrisks. Time-resolved spectral measurements confirm the‘biologically effective’ pulse duration of an IPL, duringwhich the desired wavelengths are delivered in theoptimum intensity. The time-resolved spectra were pro-duced using an HR2000+ spectrometer (Ocean Optics,Dunedin, FL, USA) and its counterpart Spectra Suitesoftware, which facilitates 3-D visualization of the pulsestructure by time and wavelength distribution.

Spatial distribution of energy

Uniform distribution of energy delivered across a treatmentarea on tissue is clearly important to avoid either ‘hotspots’or areas of under-treatment. Accurate, reproducible, andobjective data on spatial distribution of optical energy isdifficult to achieve. For the purposes of this investigation, itwas considered adequate to record energy distributionpatterns on laser alignment paper (Zap-It Corp., Salisbury,NH, USA) and analyze them using custom software toproduce assessable histograms to determine the approxi-mate energy distribution pattern.

Ocular hazard assessment

Ocular safety is one of the highest safety concerns for a light-emitting device. This assessment was made with an HR2000+photospectrometer with cosine correction in terms of spectralirradiance (Wm–2nm–1) and calibrated and traceable tonational standards. Pulse duration was determined by fullwidth half maximum (FWHM) measurement of the spectraldata. The results from these measurements were used toassess the optical radiation hazard to the human eye. Retinalthermal hazard (RTH), blue light hazard (BLH), and infrared

radiation hazard to the cornea and lens were assessed inaccordance with IEC TR 60825-9 and the InternationalCommittee on Non-Ionizing Radiation Protection (ICNIRP)Guidelines on Limits of Exposure to Broad-band IncoherentOptical Radiation, as there are no specific international IPLstandards [4].

Test results

Measured fluence

This investigation is focused on actual measured rather thanclaimed fluence values using previously published meth-odology traceable to national standards [2]. Extremes ofmeasured fluence ranges were seen where the Silk’n/SensEpil was found to be 2.8–4.3 J/cm2, whereas the rangeof the iPulse Personal was 7–9.98 J/cm2. Each device has arange of output fluences designed to prevent excessiveepidermal absorption by pigmented Fitzpatrick skin types.The Philips SatinLux/Lumea device produced measuredfluences across all available settings from 2.5 J/cm2 to6.8 J/cm2 (Fig. 2).

Spectral distribution

The iPulse Personal is intended to treat Fitzpatrick skintype’s I–IV with a 530-nm filter, the Silk’n/SensEpil to treatskin types I–IV with a 475-nm filter and the SatinLux/Lumea skin types I–V with a 575-nm absorption filter. Thethree filters are designed to remove unwanted ultravioletwavelengths from emitted output by either an absorption orreflectance filter used to attenuate lower wavelengths fromreaching the epidermis.

Fig. 2 Measured fluence valuesfor all possible settings of thetested devices in thisinvestigation

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The spectral distribution of the Silk’n/SensEpil shows atypical filtered broadband Xenon flashlamp emission with10.17% of optical energy under 500 nm, thereby signifi-cantly increasing epidermal absorption. The SatinLux/Lumea device produces pulses of light to stimulate the hairfollicle into the resting (catagen) phase, resulting inshedding of the hair shaft and inhibition of hair regrowth[9]. This device treats the widest range of Fitzpatrick skintypes (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 freedischarge technology to deliver energy to the flashlamp,and as a result, the pulse duration is a short peak of highintensity determined by the time it takes for the capacitor todischarge (Fig. 4). The time-resolved spectral ‘footprint’ ofthe iPulse Personal shows the device emitting a nearly evendistribution of energy over 25 to 60-ms pulse durations,which are within widely recognized TRT durations forsuccessful hair removal.

Safety features

The safety of a home-use device is a major considerationfor the consumer and of considerable importance toconsumer safety agencies. In the absence of an internation-ally recognized standard for intense light sources, manu-facturers of home-use IPL devices should test to theinternational technical report IEC TR 60825-9 to calculatethe retinal thermal hazard in the event of failure of contactsensors or safety pressure switches designed to preventaccidental emission of optical radiation [4].

The Home Skinovations Silk’n/SensEpil, will onlydischarge when a switch makes contact when the handpieceis pressed against the user’s skin and a trigger button on therear of the handpiece is depressed simultaneously. TheHome Skinovations latest SensEpil model uses a built-inskin color detector to prevent use on darker skin types. As aprecaution against accidental treatment at higher than therecommended energy, this device is programmed with thefluence limited to only use the lowest of five energysettings for the first 50 shots. From 50 to 150 shots, theonly energy settings that can be selected are the lowestthree levels. After the 150th shot, the device is fullyoperational. These pre-sets appear to be employed so thatthe user will feel more comfortable having used the deviceat lower levels without experiencing any adverse reactions.

The iPulse Personal uses a skin-sensitive electricalconductance safety system comprising four contact pins,which must all be in contact with coupling gel and skin forthe device to activate. The use of coupling gel with theiPulse Personal is mandated in the product insert.

The Philips SatinLux/Lumea has four push switches, whichmust all be depressed to activate the device on skin (Fig. 5).

Ocular hazard assessment

The methodology for assessing the Retinal ThermalHazard and the Blue Light Hazard has been publishedpreviously using a similar photospectrometer to theOceanOptics 2000+ [4]. Because of the low cut-off filter(475 nm) and short pulse duration (<5 ms), the highestsettings [gradient positions 4, 5], the Silk’n/SensEpil maypose a retinal thermal hazard risk in the event of failure ormisuse of the safety switch or accidental emission of lightfrom the edge of the aperture during use.

Fig. 3 Spectral distribution ofthe three measured devices allhave different cut-off filtersfrom 475 to 575 nm

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The SatinLux / Lumea and iPulse Personal were bothfound not to be a risk in the event of failure or intentionalmisuse of the safety switch or accidental emission of lightfrom the edge of the aperture during use (Fig. 6).

Spatial profile

Spatial distribution of energy from an IPL system is generallyan overlooked parameter [2]. The three devices weredischarged onto thermal laser alignment paper (Zap-It Corp,Salisbury, NH, USA) and scanned into custom software toanalyze with histograms the distribution of thermal energy

across the treatment area. A lack of uniformity couldpotentially explain side-effects such as hyperpigmentation,hypopigmentation, ineffective treatment or paradoxicalhypertricosis.

The histogram results show that the iPulse has the mostuniform distribution across its 3 cm2 treatment area (0.09 SD).The SatinLux/Lumea has a greater energy distributionlengthways across the center of its 1×3 cm (3 cm2) treatmentarea compared to the iPulse (0.21 SD). The Silk’n/SensEpilhas a greater distribution with a 0.45 SD increase of energyin the center of its 6-cm2 treatment window and a perimeterband of minimal energy. Mulholland [5] recommended

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

Fig. 5 Safety systems used bythe examined systems: the elec-trical conductance safety systemof the iPulse Personal and themechanical push switches of theSilk’n/SensEpil and SatinLux/Lumea

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overlapping the treatment areas of this device by 20% in eachdirection in his clinical assessment of the Silk’n/SensEpil(Fig. 7).

Discussion

The progression of professional hair removal from theclinic or beauty center into the home brings with it the riskof injury to the skin and eyes of consumers. In clinics andsalons, such risks are reduced by sufficient training,support, and advice from experienced professionals andthe availability of appropriate prescription medication.Evaluation of the safety mechanisms employed by home-use devices shows that they are not complex and the simplemechanical switches are sufficient to ensure that the deviceis in good contact with the skin, thus reducing the risk ofeye exposure, misuse, or accidental injury. All systemstested are attractively packaged with clear educationalmaterial for the customer regarding contraindications totreatment such as too dark skin types, active suntan andmedications. However, what cannot be so easily accommo-dated is the inappropriate purchase and use of such devicesby darker skin types than those advised by the manufac-turer. There is also scope for misjudgment of skin tonewhen selecting output settings and consequential unpleasantskin reactions caused by excessive fluence for that skin typeor alternatively under-treatment, resulting in poor efficacyin reducing hair and consequent disappointment for theconsumer. Attempts have been made by some manufac-turers, particularly in the USA, to address these problemssuch as shipping units to customers who are then requiredto obtain an activation code from the manufacturer beforethe device can be used. This gives the manufacturer the

chance to attempt to check that the user is of the correctskin tone to use the device. The US FDA has also taken alead by initially restricting the sale of at least one home-uselight-based hair removal device under a 510(k) marketingclearance to be use only under the direction of a physician,after training by a healthcare professional (Silk’n, HomeSkinovations 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 fromcustom software

Fig. 6 Comparison of themeasured weighted radiance(W m–2 nm–1) against theexposure limit value for eachsetting of the examined devices

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have to be equipped with skin-sensor technology to ensurethat they cannot be used on unsuitable dark skin types or ontanned or inappropriate pigmented skin areas.

In the absence of any recognized international stan-dard, the International Electrotechnical Commission report(IEC TR 60825-9) should be used by manufacturers tocalculate eye hazard of IPL devices in the event of failure ofcontact or failure of safety pressure switches designed toprevent emission of optical radiation. All manufacturers ofsuch home-use devices should consider testing self-useproducts against this standard and ensure that the weightedradiance values are less that the exposure limit values forcorneal and retinal thermal hazard.

Previously, the acknowledged fluence threshold forpermanent hair reduction was 5 J/cm2 required to damagehair follicles sufficiently in-situ to prevent hair regrowth[9]. Measured energy settings of both Silk’n/SensEpil andSatinLux/Lumea are less than 5 J/cm2, thus with the lowerfluence, only slight damage to the follicle might merelyresult in temporary hair growth delay by moving the hairinto the transitional Catagen (shedding) or Telogen (resting)phase [10].

The arrival of trusted brands of home-use hair-removallaser and IPL devices in the marketplace from multi-national FMCG companies may expand public awarenessand acceptance of aesthetic light-based technologies andsimultaneously lead to an increase in demand for profes-sionally delivered therapy rather than to a decline indemand for clinic-based treatments.

It is acknowledged that only one of each device wasmeasured for this study and inherent device tolerances formass production are unknown.

Conclusions

For optimum hair reduction, the user should choose adevice that delivers sufficient energy within each pulse orpulse 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 hairfollicle or at least prevent any regrowth for an extendedperiod. The ability to vary the energy density will betterallow users of different Fitzpatrick skin types control andflexibility of treatment. The designers of the devicesmeasured in this study have had to compromise productperformance by reducing manufacturing costs. Inefficien-cy of a home-use device may well cause frustration anddissatisfaction to the user, due to extended treatmenttimes and greater frequency of use.

Additional safety measures are needed to ensure thathome-use hair-removal devices are not used on suntannedskin and that treatment is restricted to the appropriate skin

tone. There is an urgent need for early ratification of thedraft international IEC 60601-1 intense light standard,which encompasses manufacturing standards for bothprofessional and home-use hair removal devices. Mean-while, home-use IPL devices should be tested to IEC TR60825-9 and the International Committee on Non-IonizingRadiation Protection (ICNIRP) Guidelines on Limits ofExposure to Broad-band Incoherent Optical Radiation toensure eye safety. This study shows that even low-fluenceIPL systems can be a risk factor to safe ocular viewing ifnear ultraviolet emission (i.e., <500 nm) is considerable.

There are several clinical efficacy studies reportingsignificant hair reduction with light-based home-use devi-ces [5–8] but they are carefully structured and monitoredand may not reflect the actual complication rate whenconsumers are using the device outside of a clinical trial.Although studies published to date on home-use deviceshave not shown paradoxical hair growth or leukotrichia atlow fluences, further work is required to understand suchside-effects. Numerous concerns exist with bringing thistechnology to market and manufacturers may be makingsubstantial efforts to address them. For example, themanufacturer of the TRIA (Spectragenics Inc, Pleasanton,USA) has a program to ensure their TRIA home-use laserhair removal device is used only on skin types I–IV,including a skin tone chart on the box, a requirement ofphone-activation where purchasers must answer questionsabout their skin type to receive an activation code and apigment detection meter that comes with the TRIA device.These steps should greatly reduce the risks associated withtanned or slightly darker skin for any user who is seeking touse the device appropriately. Most companies already haveor are developing sensors to ensure contact with skin beforedischarge of optical energy. Although not infallible, theywill prevent individuals who are using the device properly,on approved locations of the body, from accidental harmfulexposures. It is not possible to prevent wrongful dischargeby users who intentionally defeat safeguards.

Disclosures Caerwyn Ash is a PhD Graduate at the University ofWales and receives travel grants from the university. He also receivesa salary from Cyden Ltd., Swansea, SA1 8PH, UK and has a minorstock-holding in the company.

Godfrey Town is a PhD student at the University of Wales andreceives 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 keyparameters of intense pulsed light (IPL) devices. J Cosmet LaserTher 9(3):148–160

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2. Town G, Ash C (2009) Measurement of home use laser andintense pulsed light systems for hair removal: preliminary report. JCosmet Laser Ther 11:157–168

3. Ash C, Town G, Bjerring P (2008) Relevance of the structure oftime-resolved spectral output to light–tissue interaction usingintense pulsed light (IPL). Lasers Surg Med 40:83–92

4. Eadie E, Miller P, Goodman T, Moseley H (2009) Assessment ofthe optical radiation hazard from a home-use intense pulsed light(IPL) source. Lasers Surg Med 41:534–539

5. Mulholland RS (2009) Silk’n/SensEpil™ A novel device usingHome Pulsed Light™ for hair removal at home. J Cosmet LaserTher 11(2):106–109

6. Alster TS, Tanzi EL (2009) Effect of a novel, low-energy pulsed-light device for home-use hair removal. Dermatol Surg 35:483–489

7. Wheeland RG (2007) Simulated consumer use of a battery-powered,hand-held, portable diode laser (810 nm) for hair removal: a safety,efficacy and ease-of-use study. Lasers Surg Med 39:476–493

8. Emerson R, Town G (2009) Hair removal with a novel, lowfluence, home-use intense pulsed light device: preliminaryResults. J Cosmet Laser Ther 11(2):98–105

9. Manstein D, Pourshagh M, Anderson R (2001) Effects of fluenceand pulse duration for flashlamp exposure on hair follicles.Presented at the 21st annual meeting of the American Societyfor Laser Medicine & Surgery, April

10. Roosen G, Westgate G, Philpott M, Berretty P, Nuijs T, Bjerring P(2008) Temporary hair removal by low fluence photoepilation:histological study on biopsies and cultured human hair follicles.Lasers Surg Med 40:520–528

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