Page 146 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
To do this effectively, we much cool the skin. In the section ‘Optimal Skin Cooling in Laser Hair Removal’, we discussed the various techniques employed to do this. In this section we’ll discuss the basics behind these ideas.
Air is a very poor conductor of heat. That’s why we wear layers of clothing on cold days – the layers essentially traps air, which reduces the flow of heat from our bodies. If those clothes are wet, then we will lose heat much faster.
In fact, water has a thermal conductivity of around 0.6 Watts/mK (Watts per metre Kelvin), while air is only 0.025 W/mK. So, we can see that water conducts heat at around 24 times faster than air. When we generate heat energy in the dermis, which is 70% water, some of that energy will flow towards the skin surface. When it meets the air (at the skin surface), most of it will simply return back into the skin, because the conductivity of the dermal water is much greater than the conductivity of the air. The skin surface effectively acts like a heat mirror – it reflects most of the heat flow back into the skin – precisely where we don’t want it!
If we put some water-based gel on the skin surface, then the heat will readily conduct into that gel. If that gel is very cold, near-zero degrees Celsius, then the heat will prefer to flow to that point rather than back into the skin. This explains why active skin surface cooling is so important, regardless of the technology used.
Remember, the technology generates the heat in the skin - but most devices cannot properly cool it! That is very typical these days.
There is a specific technique which can be used to properly cool the skin...
Pre-cooling
Apply some water-based gel (ultrasound gel is good) to the skin surface. Wrap an ice-pack in clingfilm or thin paper (or similar) and place it on the gel. Leave it there for at least two minutes to chill the dermis effectively – this will lower the temperature of the epidermis and upper dermis, protecting them from the excess heat. In particular, this will reduce the risk of damaging the epidermal melanin in the basal layer.
With IPLs and diode lasers use the cold tip to keep the skin cool During whilst firing the energy pulse. With other systems with no contact
cooling, apply forced air or similar, to keep the skin cool (but some device tips become hot after a few shots – check to be sure!).
Post-cooling
If using a cold tip, keep it in contact with the skin for a few seconds after the pulse has been fired. The skin now has a lot of excess
________________________________________________________________________ 146 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2025