Page 153 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Hair colour / thickness
Hair colour is determined principally by the melanin content within the medulla. The more melanin contained in the hair the darker it appears. Hence the reaction of the hair to light-based treatments depends very much on the hair colour. Quite simply, darker hair absorbs more light than lighter hair.
The following chart (
Figure 85) shows how much energy density (fluence) is required to effectively denature hair of different colours and thicknesses. Clearly lighter-coloured hair requires more energy to destroy it since they absorb less energy per pulse. So light brown hair needs more energy than brown hair than black hair!
There is also a difference between thick and thin hair. This is to do with the way heat conducts away from bodies – small bodies lose heat much faster than large bodies. Hence thin hair will conduct heat away rapidly compared with thicker hair – hence they do not remain at high temperatures for any length of time, while thicker hair remains at, albeit lower temperatures, for a longer period of time.
This means that thin hair is better treated at higher fluences than thick hair to ensure destruction (higher fluences induce higher temperatures and cellular destruction occurs at an exponentially higher rate at higher temperatures – this can easily mitigate against the rapid cooling of thinner hairs). This is counter-intuitive and many operators mistakenly use lower fluences on thin hair thinking that that this is the correct approach. As we discussed previously, using a higher fluence will render the pulsewidth unimportant.
So, you must be careful when selecting the proper IPL parameters – you must consider hair colour and thickness in addition to skin colour.
Permanent Hair Removal
Required Fluency vs Hair Diameter and Color
Spectral range 600-1000 nm
120.0 100.0 80.0 Fluency J/cm2 60.0 40.0 20.0 0.0
Fine 25 um
Thin 50 um
Medium 70 um
Thick 100 um
Hair Diameter
Black Hair Brown Hair
Light Brown Hair
Figure 85 - Fluence required to damage hair vs hair colour/thickness
________________________________________________________________________ 153 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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