hair removal with a diode laser
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Hair removal with a diode laser

In order to determine the best time interval between laser treatments for most effective hair removal, scientists did a study on three different groups of patients. By treating patients at the beginning and end of a 45 day interval, a 60 day interval and a 90 day interval, scientists were able to determine which period of time would give the best results for hair removal. It has long been believed that hairs are more susceptible to laser irradiation in the early anagen stage of growth. Even though this hasn't been proven, it is still a widely held assumption that has led scientists to further investigation into the best intervals between treatments and the best stages of hair growth for optimal laser treatment.

A study was done on 176 patients who underwent hair removal with a diode laser. The laser had an 800-nm diode laser with a fluence of 25 to 40 j/cm squared. Different patients were asked to discontinue the treatment after a certain number of days so that the results could be examined over a period of five months. The final group of patients amounted to 26 out of the original 176 who were treated. These patients had been treated only on the face and neck areas of their bodies. If they had a tan or suffered from photosensitivity they had to be excluded. Similarly, if they were pregnant or using contraceptives, they were also excluded. The final group of patients was then examined after a specific number of days and they were all questioned in terms of the success of the treatment and the adverse effects that they experienced.

At the time of the follow up, an investigator counted the hairs at the location where the treatment had taken place. Patients were also asked to rate the treatment result from 1 to 4, with 1 being the poorest level of satisfaction to 4 as the greatest level of satisfaction. The treatment was deemed successful if the patient gave at least a rating of two and if there had been at least a 30% reduction in the number of hairs counted at the time of the follow up.

The results of the study were very positive in terms of finding a correlation between successful treatment and shorter time intervals between laser treatments. A total of 34% of the treatments proved to be successful according to the parameters set by the scientists. The average hair reduction in patients who underwent two of the treatment sessions was 28 %. The hair reduction for three sessions was even better at 69.6 %. The time interval between these sessions was what determined the success of the treatments such that smaller time intervals proved to be more successful than longer ones. If the patients returned for treatment after only 45 days, there was a lot less hair than if they returned at 60 days and even more hair after 90 days. This was to be expected as the longer the time between laser treatments, the more time the hair follicles had been given to rejuvenate and return to normal.

There were fifteen side effects reported by 12 of the patients. The most common of these side effects was pain in the treatment area. This was reported by 41.6% of the patients. Second, in terms of adverse side effects was the complaint of hyperpigmentation. This was reported by 12.5% of the patients. Finally blistering was reported by 12% and folliculitus was reported by 8% of the patients. The side effects seemed to be associated with the darker skin types rather than with the fluence level or the pulse duration of the laser.

Scientists explained the results of the study in terms of the interval periods being longer or shorter. When the interval was shorter, the treatment proved to be more successful. This was likely because the anagen phase of the hair follicle, which is still considered a likely factor in the success of the treatment, was still relatively “fresh”. As the anagen phase progresses, the bulb of the hair follicle goes deeper into the skin and is therefore more resistant to treatment – it is more difficult to get the laser light energy deep into the skin. Early anagen phase is therefore considered the best time for treatment and may contribute to the success of shorter intervals between treatments.

The final explanation concerning the anagen phase of growth has to do with the telogen resting phase. Up to one third of the hairs on the body can be in the telogen phase at any given time and the hairs are therefore not susceptible to the laser treatment. If the second treatment session is performed after an interval longer than the facial hair telogen phase, then the treatment will not be successful. This is because the anagen phase will already have passed for those hair follicles at the time of the second treatment. This is the reasoning behind shorter intervals of treatment. It interrupts the progression of the anagen phase before the hairs reach the telogen phase. Having discovered further evidence for the importance of the anagen phase of growth in hair removal, scientists have come one step further in understanding the laser hair removal procedure.

Hair removal with a diode laser references

  • Bouzari N, Tabatabai H, Abbasi Z, Firooz A, Dowlati Y. Hair removal using an 800-nm diode laser: comparison at different treatment intervals of 45, 60, and 90 days. Int J Dermatol. 2005 Jan;44(1):50-3. PMID: 15663662
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