Proposal and evaluation of a Monte Carlo model for hair regrowth following plucking.

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The efficacy of single or multiple hair removal treatments reveals a number of properties of the hair follicle, such as the phase in the growing cycle and the hair growth speed. The aim of the present study was to provide a method to evaluate the results of hair removal treatments, in particular plucking, in order to obtain insight into some properties of the follicle and to propose a strategy for optimal treatment. Our hypothesis is that plucking of anagen hairs may result in either reset of the follicle to telogen, in mild damage to the follicle, resulting in a temporary reduction of the mitotic activity, or in an unaffected follicle, so that the hair continues to grow. The regrowth of hairs after plucking was measured as a function of time for a number of subjects. Individual leg hairs within the areas observed were followed over time. Besides this, the growth speed of leg hairs was measured, and the extracted anagen hair length was determined to obtain an estimate of the anagen follicle depth on the leg. Monte Carlo simulations of the hair plucking and regrowth process were performed after the experiments. Some parameters derived from the experiments were used as inputs; others were fitted to achieve a good correlation between the result of the simulations and the experiments. Finally, the Monte Carlo routine was used to investigate the influence of the time interval between multiple plucking treatments. The regrowth of hairs after plucking, the growth speed and the extracted anagen hair length were measured. Both experiments and Monte Carlo simulations indicated that the result of plucking of an anagen hair is not limited to reset of the follicle to telogen or continued hair growth, but that a temporary reduction of the mitotic activity is very likely to occur. Finally, a linear relationship between the interval between epilation treatments and the average number of hairs on the skin was found using the Monte Carlo simulation. The combination of experiments and Monte Carlo simulations is a very successful strategy for studying hair removal and hair (re)growth in detail.