Page 86 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Upper zone – In the superficial part of the skin most of the energy is absorbed by constituent tissues. Hence, most of the desired photothermal reactions will occur in this zone. If the incident energy is too high then unwanted tissue damage may also occur. This can be mitigated with proper and sufficient skin surface cooling, preferable contact-cooling (due to its higher efficiency compared with other methods) – see Figure 38.
Figure 38 – Zones of the skin where reactions may, or may not, occur
Middle zone – this zone occupies a range of depths where there is insufficient available energy to ensure the desired response in the target tissues. During photothermal treatments some of the targets may be only “reversibly denatured” leading to a disappointing clinical outcome. Hair follicles can recover and regrow as thinner, finer hairs – which are more difficult to destroy. Deeper follicles, such as bikini or arm pits, consequently, require higher fluences at the skin surface to ensure their destruction.
Deeper zone – at this depth there is insufficient absorption of the incoming light energy to induce any significant or useful reaction in the target tissues. Increasing the incident irradiance at the skin surface will increase the amount of available energy at these depths and push the non-reactive zone deeper. But this strategy may result in excessive thermal damage near the skin surface. Hence, much more cooling would also be required.
As a consequence, we must choose the most appropriate parameters (settings) to ensure the desired results at the required depths (where our targets are located), whilst protecting the upper layers of the skin.
________________________________________________________________________ 86 Chapter 3 Laser/IPL Hair Removal
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