BMLA talk 2024 - Pre- and post-cooling is important in photothermal treatment in reducing pain

In this talk I discuss my 1-dimensional computer model which looks at the temporal evolution of the heat distribution, during and after irradiation of hair melanin. During longer pulsewidths (more than 1ms) heat can ‘escape’ from the absorbing melanin into the surrounding tissues. As a consequence, the temperatures in the melanin are not as great compared with shorter pulses. Hence, longer pulses generate lower temperature in the hair, for the same fluence (and wavelength). But, is this important? If the real targets are the germ cells in the bulge. Located on the follicle wall, then we must consider the temperature at those locations too. The heat energy diffuses from the melanin in the hair shaft, and eventually reaches the bulge. In doing so, the values of the temperatures change significantly. My talk discusses this change in the temperature distribution and the consequent effects on the germ cells. My conclusion is that the initial pulsewidth has no direct effect on the temperature-time histories of the germ cells in the bulge. So, the pulsewidth is not important. The total energy absorbed by the melanin is the important characteristic.