Page 93 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Laser/IPL hair removal requires the target follicles to reach a sufficient temperature for a sufficient time to ensure full denaturation of the stem cells. Higher temperatures require lower heating durations, according to the Arrhenius Damage Equation. If the correct parameters are delivered to the follicles, then the overall efficiency of the process depends entirely on the skills and abilities of the laser/IPL operator.
In reality, the effective kill rate will be typically between 20 and 90% in each treatment session, depending on those skills. That EKR has a significant effect on the number of repeat sessions required to generate a satisfactory end-result.
Our model shows clearly the optimum intervals between sessions. Applying the industry ‘standard’ interval of 6 to 8 weeks into the model shows that between 6 and 10 repeat sessions are required – as is typically found in real-world settings. This confirms the accuracy of our model reasonably well.
A quick calculation of the surface area occupied by hair per square centimetre across the body, reveals a range from around 1.5% (legs/axillae) to around 13% (chin/upper lip). This indicates that most of the light energy delivered in hair removal treatments is not actually absorbed by the targets, thereby reducing the overall efficiency, and increasing the likelihood of generating unwanted tissue damage.
Natural reticence to ‘injure’ patients (“fear factor 1”) typically results in operators choosing less than optimum parameters, particularly the fluence. The authors’ experience in this field also indicates that many operators do not properly understand the importance of pulsewidth, which essentially determines the supra-threshold ‘cooking time’ of the target cells. In most cases, the denaturation time is not equal to the pulsewidth. As a consequence, achieving a high EKR can be difficult, in many situations, leading to an excessive number of treatments.
Conclusions
The results of our model depend greatly on the Richards and Merhag observational data. If new, more accurate, growth cycle data becomes available in the future, then it is easy to input it into the model and generate new interval data.
From Table 19, it is clear that this treatment is a case of ‘diminishing returns’. Each treatment can kill a certain percentage of follicles, but every time a client/patient returns, there are fewer follicles to treat.
Our results are, in some cases, significantly longer than are currently adopted in the commercial world. It is unlikely many laser/IPL operators will wish to leave gaps up to 26 or 32 weeks between treatment sessions, preferring to stick to the ‘standard’ 8 weeks instead. While this will achieve the same end-goal, it will result in many more sessions. That’s a commercial decision. However, it is clearly more important to improve the EKR which can only be achieved through proper choice of wavelength, fluence and pulsewidth.
________________________________________________________________________ 93 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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