Final answer:
Permanent hair removal requires multiple treatments per follicle to be effective due to the natural cycles of hair growth. Laser hair removal targets the follicle during the growth phase, but as not all follicles are in this phase simultaneously, several sessions are needed for lasting results. Methods like shaving are temporary because they do not target the hair follicle itself.
Step-by-step explanation:
The process of permanent hair removal involves multiple treatments of the same hair follicle to achieve lasting results. Hair removal methods, such as laser treatments or electrolysis, necessitate repeated sessions due to the nature of hair growth cycles. Hair growth begins inside a follicle when stem cells divide to produce new keratinocytes, which eventually form the hair shaft. The active phase of hair growth (anagen) is followed by a transitional phase (catagen), and finally a resting phase (telogen), during which the hair eventually falls out and a new hair begins to grow. Because not all hair follicles are in the same phase at the same time, multiple sessions are needed to target them during their growth phase.
Methods such as shaving and the use of chemical depilatories are considered depilation methods, and they only remove the part of the hair above the surface of the skin. In contrast, permanent hair removal methods target the follicle itself. These methods are more intricate, as they aim to destroy or disable the hair follicle from producing future hairs. Due to the cyclical nature of hair growth, several treatments are typically needed to permanently reduce hair growth. Treatments such as laser hair removal work by targeting the melanin in the hair follicle during the anagen phase, which is when the follicle is most susceptible to damage; however, as follicles enter different phases, multiple sessions become necessary to address all follicles effectively.
While this question touches on the treatment of hair follicles, there are analogies in the medical field such as the use of human menopausal gonadotropin (hMG) or follicle stimulating hormone (FSH) to stimulate follicles in the ovaries for fertility treatments. Such treatments also recognize the importance of follicular phases and are administered with the understanding that not all follicles will respond at the same time, therefore requiring a carefully timed series of interventions.
In conclusion, permanent hair removal requires multiple treatments per follicle due to the cycles of hair growth, with each treatment targeting the follicle at the active growth stage. As with many biological processes, timing and repetition are key to affecting a long-lasting change.