The phenomenon occurring in the beauty industry called ‘light induced hypertrichosis’ (L.I.H) is causing some interesting and challenging situations, recently I have been asked to provide advice and information on why this situation arises in clients who have been treated with light based devices (IPL & Lasers). L.I.H seems to occur down the track in clients who have undertaken a series of Intense pulsed light (IPL), and in some case after laser hair removal. (i.e.: 12-18 months)
We understand exactly why this happens but this should not be confused with ‘paradoxical hair growth’ which describes when hairs adjacent to the treated areas can be stimulated to grow new hairs, this is a rare, but normal and unexplained side effect that can occur due to bio-stimulation from the light. Unfortunately clients are unaware of these scenarios and unaware that some clinics are touting stories about why the hair is still coming back.
The first priority we must address is that the target (in this case hair) sits at varying depths in the skin, some terminal hairs have been speculated to be sitting as deep as 5mm-6mm, vellus hairs sit closer to the surface of the skin and therefore provide an easier target (supposedly), laser physics show light sources rely on a chromophore or target (melanin being the most effective) to attract the light to, therefore creating heat in sufficient enough degrees to cause fatal destruction of the target. However, here poses a potential problem, if the light being transmitted into the skin cannot reach the target, or more importantly the light is distracted by other natural targets such as melanin in the dermal / epidermal junction, what happens?
Wavelengths lower than the infrared threshold of 700nm have a much higher affinity to melanin, they cannot penetrate deeply into the skin because the light source is ‘distracted’ by melanin targets in the surface tissue layers. In darker skin types V and VI they led to unacceptable rate of complications like epidermal burns and post treatment hyper pigmentation due to this strong competing epidermal melanin, in some cases even in Fitzpatrick III with high degree of sun damage known as actinic bronzing, and lighter Fitzpatrick IV skin types will be adversely affected from a safety point of view when these lower wavelengths are used for hair removal.
Let’s look at the science as this is something that can’t be negotiated. Wavelengths emitted from broadband, polychromatic light sources such as in the case of IPL devices have limited depth of penetration so they will always be limited in what they can reach under the skin. In the case of wavelengths over 700nm, the light source is able to reach slightly deeper and s the nanometres go up in number the less likely the light is to affect the superficial targets meaning it will penetrate deeper into the skin, these longer wavelengths 750-900nm for IPL and 755-1064nm for Laser are more effective at reaching hair targets in the deeper layers of the skin. For example 3-4mm or 5-6mm respectively based on their ability to transmit without competing chromophores.
Unfortunately Food and Drug Administration (FDA) clearance is easier to achieve than many believe, and so when you read that a system is ‘FDA cleared’ for darker skin types, I’d advise you to clarify the science behind how this works by addressing the wavelength issue. Companies who can safely treat darker skin types will be able to show that safety is not a problem, even when higher fluences and shorter pulse durations are used. After all ideally a laser / IPL professional would never want to compromise on delivering results for their client.
Confused, need more facts or clarification? – feel free to contact me personally.
Our aim is to increase the education and understanding on these topics so that you, the Laser / IPL therapists may be able to ask the right questions from your suppliers and other industry training providers.
To contact Ruth please see her details here.