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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