Static and dynamic modes of 810 nm diode laser hair removal compared: A clinical and histological study

Abstract

Background and Aims

Laser hair removal has recently become a major indication. Diode lasers have become commercially available offering two modes of application: a stamping or static mode, and a dynamic mode whereby the handpiece is continuously moved across the target tissue. The present study was designed to compare the efficacy of these two approaches clinically and histologically.

Subjects and Methods

Twenty-five subjects participated in the study, 12 males and 13 females, ages ranging from 20 to 57 yr (Mean age 41.6 yr). A baseline hair count was performed on both the target areas. The ms-pulsed diode laser delivered 810 nm via a handpiece with a cooled tip, offering both static and dynamic modes which were used on the subjects' left and right crura, respectively. Pain during treatment was assessed using a visual analog scale (VAS) and gross inspection was performed immediately after treatment for any abnormality in the treated skin. Hair counts were performed on both crura at 1 and 3 months after the treatment, and compared with the baseline counts. Biopsies were performed in the dynamic mode treated skin at baseline and at 1 month after the treatment, and assessed with light microscopy, immunohistochemistry and transmission electron microscopy (TEM).

Results

All subjects completed the study. Compared with baseline, hair counts were significantly lower at 1 and 3 months post-treatment with no significant difference between the static and dynamic laser depilation modes, nor in the severity of the pain experienced during the procedure. Histologically, degenerative changes in the hair follicles were noted immediately after laser treatment. At one month, cystic formation was seen in the hair follicles showing a strong tendency towards apoptotic cell death.

Conclusions

With the diode laser system and at the parameters used in the present study, high depilation efficacy was seen with no significant difference between the static and dynamic modes. Interestingly, good long-term depilation is probably a result of induced apoptotic cell death in the follicles rather than any other mechanism.

Introduction

The demand for depilation is a very strong consumer-driven cosmetic indication. According to data published in 2011 by the International Society of Aesthetic Plastic Surgeons (ISAPS) ¹⁾, depilation was ranked as the third most frequently performed non-surgical procedure at medical facilities, with over 75,000 patients undergoing this procedure annually.

Historically, depilation has been achieved with plucking, shaving, wax depilation, electrolysis and so on, but since the 1990s, laser depilation has become the predominant depilation technique employed at medical facilities ^{2, 3)}. Intense pulsed light (IPL), delivering pulses of broad-band polychromatic noncoherent light with appropriate cut-off filters, has also attracted attention, but although the cost of systems is lower than for lasers, depilation efficacy is less with repeated sessions required. ⁴⁾ IPL systems therefore tend to be found in so-called aesthetic clinics rather than in medical practices where lasers, including diode lasers, are preferentially used in medical practice because of the higher efficacy and fewer sessions required.

Several new laser devices have been developed for laser depilation, including handpieces with a large treatment area, systems delivering serial shots, powerful cooling systems and so on. Some other devices, including the one used in the present study, ^5–7) deliver the laser energy with the handpiece in constant contact and continuous motion over the treatment area, referred to as the dynamic mode, compared with the conventional ‘stamping’, or static, mode. The dynamic mode can potentially cover a larger area in less time with less ‘skipping’ of untreated areas, and possibly with less pain. ^{6, 7)} Few studies have histologically, immunohistochemically and ultrastructurally compared the efficacy of these two modes, in addition to hair count post-treatment compared with baseline counts. The present study was therefore designed to compare the safety and efficacy of the static and dynamic modes of an 810 nm diode laser system on contralateral limbs of the subjects with the above assessments, including pain evaluation.

Subjects and Methods

The study population comprised 25 subjects wanting leg hair removal and who met the inclusion criteria. There were 12 males and 13 females, mean age, 41.6 yr with an age range of 20 to 57 yr (Table 1). Exclusion criteria were any skin disease in the area to be treated, any circulatory impairment, presence of uncontrolled diabetes or other systemic disorder, pregnancy, and the inability to give informed consent.

Table 1: Patient demographics and hair count per cm² at baseline (B/L), at 1 months after treatment (A1) and at 3 months after treatment (A2) for both static mode- and dynamic mode-treated legs.

PatIent No	Sex	Static mode			Dynamic mode
		B/L	A1	A2	B/L	A1	A2
1	M	18	3	7	20	3	10
2	M	15	11	8	19	11	8
3	M	9	6	4	7	4	5
4	F	10	7	8	18	6	5
5	F	2	1	1	8	5	2
6	F	14	4	4	14	5	4
7	F	7	6	3	8	7	5
8	M	25	20	21	29	18	22
9	F	9	5	2	18	6	5
10	M	20	13	15	21	15	11
11	M	24	3	15	20	3	10
12	M	20	16	15	14	12	13
13	M	22	11	15	24	12	15
14	M	33	18	20	26	8	16
15	F	16	14	15	16	11	12
16	F	20	9	5	19	12	7
17	M	27	20	27	31	20	29
19	F	13	11	3	16	5	6
20	F	5	2	2	6	2	3
23	F	2	1	2	1	1	1
24	F	7	4	5	6	3	2
25	M	24	13	23	27	19	25
26	F	11	3	4	8	3	3
27	F	21	13	24	23	15	25
28	M	27	21	4	31	23	8

The system used in the present study was a diode laser specifically designed for hair removal (Soprano ICE, Alma Lasers, Israel). The system delivered laser energy at 810 nm in the present study with a treatment window of 20 mm × 10 mm (2 cm²). The system offered the static mode, whereby treatment is performed in a series of adjoining “stamps” using a repetition rate of 1 Hz, i.e. one pulse per second. It also offered the dynamic mode, whereby the handpiece is kept in continuous motion with the handpiece cooling plate in constant contact with the skin, using a repetition rate of 10 Hz. A hair count per cm² was performed on both legs to establish the baseline values pretreatment.

After shaving both crural areas of the subjects, the laser was applied in static mode to the left crus at an energy density of 30 J/cm² per pulse, pulse width of 55 msec and a repetition rate of 1 Hz, aligning each 2 cm² shot carefully to minimise overlap. The dynamic mode was used on the right crus, moving the handpiece constantly back and forth over the target area as recommended by the manufacturer at an energy density per pulse of 10 J/cm², a 20 msec pulse width, and a pulse rate of 10 Hz, which gave an energy density per 100 cm² of 100 J/cm². A cooling gel was applied in both modes, not only to help to cool the skin, but to ensure good optical coupling between the handpiece window and the target tissue.

Immediately after treatment, the treated areas for both static and dynamic mode were subjected to gross clinical observation to check for excessive erythema, edema or any other adverse event in the skin. Subjects were interviewed regarding the pain felt during treatment for both modes, using an 11-point visual analog scale (VAS) to give a numerical pain rating, ⁸⁾ scoring from zero to 10, where zero was no pain and 10 was the worst possible pain the subjects had experienced. They were also asked to identify any other form of discomfort, such as stinging or itching. Further hair counts per cm² as above were taken at 1 and 3 months after the single treatment session for both modes, and compared with the respective baseline values. Clinical data of the hair count and the pain VAS scores were analyzed statistically with a paired Student's t-test for comparison between the static and dynamic modes.

Three millimeter punch biopsies were harvested from the right crus (dynamic mode) immediately after treatment, and specimens were routinely prepared for hematoxylin and eosin (HE) staining for light-microscopic examination, proliferating cell nuclear antigen (PCNA)/p53 immunohistochemistry for identification of apoptotic characteristics, and ultramicromorphological staining for examination under a transmission electron microscope.

This study was conducted with advance approval obtained from the Japan Aesthetic Dermatology Symposium Ethical Committee, and carried out in alignment with the precepts of the Declaration of Helsinki as ratified in 2013. Having had the purpose of the study explained to them in full, all subjects gave oral and written informed consent to participate in the study, and for the use of fully depersonalized data

Results

Clinical observation

Of the 25 subjects, 1 developed erythema of the crural skin on both the static (left) and dynamic (right) sides, and 2 developed mild erythema of the crural skin on the dynamic side; the erythema appeared immediately after the laser application in all 3 subjects. No edema was noted in any subject on either side. In the subject with erythema of the crural skin on both sides, the erythema persisted until the following day. In the 2 subjects with erythema on the dynamic side, the erythema had disappeared by the following day. At one month after the laser application, no skin changes, including postinflammatory hyperpigmentation (PIH) were observed on either of the diode laser-treated areas. No other adverse reactions were noted after the laser application, on either the static or dynamic mode treated areas.

Hair count at 1 and 3 months after the laser application compared with baseline

The mean hair counts per cm² before and at 1 and 3 months were 16.04, 9.40 and 10.08, respectively, on the static side, and 17.20, 9.16 and 10.08, respectively, on the dynamic side (Figure 1). Table 1 shows the hair counts per patient at baseline and at the 1- and 3-month assessments for both left and right legs, and Table 2 shows the statistical examination of the paired data. The hair count per cm² at baseline was slightly higher for the dynamic mode-treated side, but without significance (P = 0.1480). The hair counts at 1 and 3 months after the laser application differed extremely significantly from the count recorded before the laser application on both the right (dynamic mode) and left (static mode) sides (p < 0.0001 for both, two-tailed paired student's t-test, 95% confidence interval). However, there were no significant differences in the hair counts between the sides treated in the dynamic or static modes at any assessment time-point.

Fig. 1:

Hair count per cm² at baseline and 1 and 3 months after laser application in the static (1a) and dynamic (1b) modes. *** denotes extreme statistical significance (P < 0.0001, Table 2)

Table 2: Statistical analysis (two-tailed paired Student's t-test) with p =< 0.05 as significant.

Tested pair	Mean ± SEM	P value	Sig
S-B/L vs S-A1	16.04 ± 1.68 vs 9.40±1.27	< 0.0001	HS
S/BL vs S-A2	16.04 ± 1.68 vs 10.08 ± 1.62	< 0.0001	HS
D-BL vs D-A1	17.20 ± 1.69 vs 9.16 ± 1.26	< 0.0001	HS
D-B/L vs D-A2	17.20 ± 1.69 vs 10.08 ± 1.58	< 0.0001	HS
S-B/L vs D-B/L	16.04 ± 1.68 vs 17.20 ± 1.69	P=0.1480	NS
S-A1 vs D-A1	9.40 ± 1.27 vs 9.16 ± 1.26	P=0.7114	NS
S-A2 vs D-A2	10.08 ± 1.62 vs 10.08 ± 1.58	P=1.0000	NS

HS, highly significant; NS, not significant

Pain score

Pain scores as rated on the VAS ranged from 0 to 10 with a mean of 2.73 on the static side, and from 0 to 10 with a mean of 3.49 on the dynamic side. One subject developed an itching sensation on the static side. There was no statistically significant difference in the mean pain VAS scores between 810 nm laser depilation in either the static or dynamic mode, although scores tended to be slightly higher in the dynamic mode.

Histological findings

Immediately after laser application on the dynamic side (Figure 2), the HE staining of specimens revealed enlargement of the space inside the hair follicle accompanied by vacuolation, with the structure of the hair showing degeneration and appearing as a basophilic mass. The polarity of the hair follicle cells was also markedly disturbed, with sporadic intense degeneration, making the cell structure difficult to identify. The basal membrane of the outer root sheath was also disturbed in part, resulting in a slightly edematous appearance of the perifollicular tissues.

Fig. 2:

Hair follicle structure immediately after laser depilation in the dynamic mode. The area shown in this figure is estimated to be in the vicinity of a bulge, judging from the neighboring sebaceous gland structure (S). The space inside the hair follicle is enlarged, accompanied by vacuolation (black arrowheads), and the hair structure has degenerated, assuming the form of a basophilic mass. The polarity of the hair follicle cells is also markedly disturbed, sporadically accompanied by degeneration intense enough to make the cell structure unclear (white arrowheads). The basal membrane of the outer root sheath is also disrupted in parts, with the dermal tissue around the hair follicle being slightly edematous. (HE stain)

Ultramicromorphological observation immediately after the laser application (Figure 3) also revealed slight edema of the hair follicle cells in specimens from the dynamic-treated side, partially accompanied by separation of the hair follicle cells. The basal membrane of the hair follicle also showed degeneration, demonstrating a stratified form. At 1 month after the dynamic treatment, degenerated hair follicles and cystic hair follicle structures were noted histologically in specimens, with the follicle cells failing to show a positive chromatic response to PCNA staining and showing only a partially positive chromatic response to p53 staining (Figure 4).

Fig. 3:

Ultramicromorphological (transmission electron photomicrograph) findings immediately after the laser depilation in the dynamic mode. Ultramicromorphological examination immediately after the laser application revealed slight edema of the space of the hair follicle cells on the right side (white arrowhead), with partial separation of the hair follicle cells. The basal membrane of the hair follicle has also assumed a stratified form and become degenerated (black arrowheads), with the dermal layer on the left side being edematous and showing collagen fiber degeneration.

Fig. 4:

p53 staining at 1 month after laser application in the dynamic mode. p53 staining reveals enlarged hair follicles on the cyst (black arrowheads), accompanied by a partially positive chromatic responses of the hair follicle cells.

Discussion

Wax depilation and electrolysis have been used for removal of unwanted hair for decades. Until the 1990s, electrolysis was the only method available for ‘permanent’ depilation. After advances in laser technology and indications in the 1990s, laser depilation became widespread ^{2, 3)}. On the other hand depilation devices based on polychromatic and noncoherent broad-band intense pulsed light, with appropriate cut-off filters, were also reported, and found use in aesthetic salons. More recently, hand-held home use IPL systems have also appeared on the market. Although offering some efficacy, reports suggest that multiple treatments are required, and even then regrowth can occur. In addition, paradoxical hair growth has been reported on areas adjacent to the areas treated. ⁹⁾ With their higher efficacy and need for fewer treatments, laser systems (including diode lasers) with depilation as their main indication, or one of their main indications, have therefore offered a more effective way to provide depilation for patients in the medical and clinical setting as an economically profitable service.

Recent devices have offered improvements on the original design including larger treatment areas per shot, systems delivering serial shots, cooled treatment windows and so on. Other systems offer two delivery modes, both of which are applied following application of a cooled gel to the skin which not only helps to protect the epidermis from excessive thermal damage, but also helps to couple the laser energy from the handpiece into the skin to increase efficacy. In the static mode, the traditional hair removal approach, the handpiece is moved from shot to shot, carefully abutting the treated areas to prevent overlapping and therefore dumping in extra heat which could lead to unwanted side effects. The laser is set to 1 Hz, with the footswitch continuously depressed. The alternative approach involves using the laser set to a high pulse rate, such as 10 Hz, 10 pulses per second, and, keeping the handpiece and treatment cooling plate in contact with the tissue, the handpiece is moved to and fro continuously. This is called the dynamic mode, The system used in the present study was one such diode laser with a large 20 mm × 10 mm treatment window. The static mode was used on one of each subject's legs, whereas the contralateral leg was treated with the dynamic mode which has been reported to enable swifter hair removal over larger treatment areas, such as the entire leg or back with good efficacy and potentially less pain. ^{6, 7)}

In the present study, the parameters used at a wavelength of 810 nm and a 20 mm × 10 mm treatment area per shot were a 30 J/cm² energy density and a 55 msec pulsewidth for the static mode at a repetition rate of 1 Hz, and an energy density of 10 J/cm² and pulsewidth of 20 msec for the dynamic mode at a pulse rate of 10 Hz. Coupled with the to and fro motion used with the continuous handpiece over the tissue, this allows a relatively high energy density of 100 J/cm² over a 100 cm² treatment area: that represents 10 Kj total energy delivered over the 100 cm² area, allowing for efficient hair removal.

The system also offers the wavelengths of 755 nm and 1064 nm. The wavelength of 810 nm was chosen over 755 nm based on the higher density of epidermal melanin associated with the Japanese skin type III, thus offering more safety while still achieving high absorption in the melanin in the hair and follicle.

In the static mode, the system was applied shot by shot at a repetition rate of 1 pulse per second (1 Hz). Care is needed to prevent overlapping of treatment areas per shot, and to ensure that there are no skipped areas between shot patterns, The dynamic mode with a rep rate of 10 Hz helped to prevent both these possible faults thanks to the continuous motion applied to the handpiece, especially when used with the coupling and cooling gel, which helped the handpiece to glide more smoothly over the target tissue. On the other hand, practice and experience are required in the dynamic mode to ensure optimum uniformity of energy delivery over the entire treated area.

After the depilation treatment, erythema was seen on the static mode side in 1 case and on the dynamic mode side in 3 cases (including one case that showed erythema on both sides). Royo et al. ⁵⁾ reported erythema in most patients as well as outbreak of pigmentation in some cases. In the study conducted by Royo et al., the skin type was III, IV or V (among others, type V accounting for 57.3% of all cases). The difference in the distribution of the skin type in the present study as compared to that in the study by Royo and colleagues probably explains why adverse reactions were much less frequent in the present study.

Pain evaluation using the VAS is a method by which the subject rates the level of pain during the laser application by selecting one of 11 grades in the range of 0–10 ⁸⁾. The subject is asked to rate the grade of pain in comparison to the most intense pain that he/she has experienced before (= grade 10). Grade 0 indicates no pain, 1 through 3 indicate mild pain, 4 through 6 indicate moderate pain and 7 through 10 indicate strong pain. In the present study, the mean numerically-rated pain score was 2.73 for the static side, and 3.49 for the dynamic side, with no significant difference between the two modes. Koo et al. reported the results in their study using a similar scoring system, ⁶⁾ wherein they obtained a mean score of 3.6 for the single pulse static mode and 2.7 for the dynamic mode, with the pain significantly less frequent in the latter. In the Koo study mentioned above, the diode laser delivering the single shot static mode was from a different manufacturer than the one used in our present study, which could explain the difference in the score. However, in our scoring also, using the score range of 0 to 10 for both the static and dynamic modes, it must be noted that large inter-individual differences in the perception of pain could have affected the results.

In regard to evaluation of the depilation efficacy of the device, one session of laser application resulted in a significant decrease of the hair count at 1 and 3 months for both the static and dynamic approach. Braun ⁷⁾ also conducted a comparative study with different systems, and reported the effectiveness of depilation with laser application in both the static and dynamic modes, adding that the efficacy did not differ significantly between the two modes. Koo and colleagues in their study conducted a similar comparison between two types of device for static and dynamic modes, reporting that the rate of hair count decrease was slightly higher for the dynamic mode, although the difference was not statistically significant.

In the present study, the rate of hair count decrease at 1 month was 41.4% for both the static and dynamic modes. According to the report by Koo et al., the rate of hair count decrease was 52.7% for the single pulse mode and 57.6% for the dynamic mode, with no statistically significant difference between the two modes. In the present study also, the efficacy did not differ significantly between the two modes.

Histologically, hair structure degeneration, disturbance of the hair follicle structure and edematous degeneration of the surrounding dermis were noted. These findings were confirmed by ultramicromorphological observation. These changes seen following laser application were akin to the changes seen after application of the ruby laser or alexandrite laser reported previously by our group ^{10, 11)}.

Furthermore, the hair follicle tissue assumed a cystic form and showed positive staining for p53 at 1 month, indicating that the hair follicles with these features would disappear by means of apoptosis. Also in the present study, there was no clinical evidence of inflammatory reaction after the laser application. Prior to the present report, no inflammatory reaction other than application-induced folliculitis has been reported as a depilation-associated inflammatory reaction. We can thus estimate that the disappearance of the hair follicle structure following laser depilation cannot be regarded as a granulomatous reaction, and the findings of the present study suggest the involvement of apoptosis.

Conclusions

The diode laser device evaluated in the present study showed high depilation efficacy in a Japanese trial population, confirming previous reports. There was scarcely any difference in the outcome between the static and dynamic modes, although there was high statistical significance in the differences between the baseline and follow-up hair counts for the two modes. Because of its capability of operating at a higher repetition rate and in constant motion, the dynamic mode would appear to be more suitable for depilation of extensive areas, such as the trunk, thighs and legs, while the static mode better lends itself to sites with an irregular surface or which present areas which are difficult to reach, such as the face and axilla. Therefore, given their equal efficacy and safety, it is advisable to select between the static and dynamic modes depending on the requirements of each individual case.

Conflict of Interest

The author declares no conflict of interest concerning the device used in the present study