Page 19 - Mike Murphy's Blog Posts

A6 - Laser/IPL Hair Removal – Can it really be “pain-free” and still be effective?
Many laser/IPL hair removal systems claim to be “pain-free”. However, this is mainly because they output such low energies that insufficient temperatures are generated in the hair follicles, making them pretty useless...
So, can laser/IPL hair removal really be ‘pain-free’ but still effective? Well, yes...
Epidermis
When light energy is fired into the skin it first encounters the epidermis. Some of the energy will be absorbed by the melanin located throughout the epidermis, but particularly in the basal layer between the epidermis and the dermis.
Consequently, the basal layer becomes hot quite quickly, since most of the melanin and melanocytes are located there. Darker skins will generate higher temperatures purely because of the higher melanin content.
This can be problematic since this heat may cause tissue damage, in both the epidermis and dermis. In particular, blisters are formed here, usually due to excess light energy!
In addition, while pain/temperature nerves are located throughout the dermis, the concentration is higher near the skin surface (for survival reasons). This means that we feel high temperatures more when they occur near the skin surface – hence, high basal layer temperatures are painful. This clearly suggests we need to cool this layer significantly.
Dermis
The rest of the light energy will progress into the dermis. Now, it is important to understand that the dermis is a highly scattering medium which causes the photons to ‘bounce around’ all over the place!
As a direct consequence of this scattering, a significant proportion of the light energy is back-scattered out of the skin altogether. PA calculated that up to 50% of the light entering the skin may be lost in this way. In other words, if you fire 5 J/cm2 into the skin, only around 2.5J/cm2 stays in the skin!! However, this depends on the wavelength (strongly), the amount of melanin and the target concentration.
Of the light energy which remains in the dermis, less than 1% will be absorbed by the target hair follicles. This is simply because the volume of hair follicles within the dermis is very small compared with the other tissues. In some cases, the amount absorbed can be less than 0.01%!
Mike’s Blog Posts 19