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RELATIONSHIP BETWEEN HAIR CYCLE AND LASER HAIR REMOVAL : OPEN STUDY ON 492 SESSIONS

By Dr Catherine GAUCHER - Dermatologist
La Roche-Posay (France)
e-mail : catherine.gaucher@wanadoo.fr 

This study araised from the observation of our clinical results. In order to obtain the best « cost-benefit » index for our patients, we asked them to come back as soon as the hair was growing up again, as they would priorly do while waxing for example ; they were asked not to wait neither to perform any other method of hair removal between the laser sessions. For the patients who were able to follow this rythm, we could notice that the results were much better, and that the delay of regrowth, related to the hair cycle, was following a regular graph which mathematical formula was to determine. This is the purpose of this paper.

FUNDAMENTAL NOTIONS

Hair removal in human being involves many factors which we shall remember before study.

Two different types of hair have been described : vellus and terminal hair, which includes scalp, eyebrows and big hair visually evident on the body. Terminal hair are a few millimeters to a few centimeters wide.

Some authors have described a third categoryof hair, which they called « medium », which are not big but can show the presence of a medulla, which the vellus do not have.

Terminal hair is composed of :

• - the medulla
• - the cortex
• - the cuticula

The intra-epidermal part of the hair is composed of :

• - infundibulum (until the glandula sebacea)
• - isthm (glandula sebacea and arector muscle of hair)
• - epithelial gaines region
• - hair bulb, around the follicular papilla.

The innervation of this part is very rich.

Some of these structures are transitory, others not : the permanent parts are those we want to destroy to achieve permanent hair loss.

Vellus differ from terminal hair by their thinness, thier low pigmentation and their absence of medulla.

Hair have different characteristics according to their localisation, the age, the sex, and the ethnia of the patient.

The riche innervation of the papilla is noticeable and can explain the pain which is ALWAYS PRESENT in any method of really efficient and permanent hair removal. When there is no pain at all, the hair bulb and papilla can not be destroyed and therefore the efficacy of the method is doubtfull. Anyway, laser hair removal is probably the least painfull method for hair removal nowadays.

On another hand, hair growth in human being is regulated by cycles, called hair cycles, which have the particularity of not being synchronised (as they can be in some animals, who change their hair periodically, and all at once…). The few papers existing in that field show that the hair cycles greatly vary from one zone of our body to another. For example, the hair cycle of the upper lip is about 4 to 5 months, when the hair cycle of the leg is about 18 to 24 months !

These considerations are important to know before beginning hair removal, whatever we use one or the other existing method, because they influence the results and the expectatives we can give the patient before the treatment.

In fact, it seems to us totally non logical to ask the patient come back at the same interval while treating an upper lip or a leg. We shall show later why this is not correct.

BASIS OF LASER HAIR REMOVAL

This method, recently introduced (1996 in USA and 1997 in France), shows a certain amount of good results and advantages and will probably be more and more developed in the future.

THE BASIS OF LASER HAIR REMOVAL :
SELECTIVE PHOTOTHERMOLYSIS

LASER TARGETS

According to the selective photothermolysis principal, the laser targets are able to catch the energy of the laser beam and to convert it into heat. The selectivity is obtained by the presence of a chromophore which color is the same as the color of the laser beam (the absorption spectrum of the chromophore is included in the absorption spectrum of the laser).

In human hair, the main chromophores are :

• - melanin
• - oxy and desoxyhemoglobin
• - water
• - may be others not yet identified.

Melanin is the most selective of these chromophores. It is essentially located in the hair and the bulb, which are then the major targets of the laser beam.

SELECTIVE PHOTOTHERMOLYSIS

Melanin is present in the epidermis too, so the selectivity of photothermolysis will depend on the difference of melanin concentration between the epidermis and the hair and on the thermal relaxation time (TRT) of these two structures.This is what we call : selective photothermolysis.

The thermal relaxation time (TRT) of melanin in the epidermis is 3 to 10 ms and the TRT of melaanin in the hair follicule is 40 to 100 ms ; then the pulse duration time for the laser must be at least 10 to 40 ms to be efficient.

SELECTION CRITERIAS OF A HAIR REMOVAL LASER

Regarding these basic notions, we can conclude that all hair removal lasers can not pretend to achieve the same efficacy . A synthesis was proposed by US MDs in the end of 2000. They consider a laser can pretend to achieve a permanent hair reduction when it presents the following criterias :

• Wavelength = 700 to 800 nm (best absorption by melanin)
• Spot size > 5 mm (best penetration for deep hair)
• Pulse duration > 20 ms (depends on the hair diameter, which gives the TRT)*
• Fluence > 30 J/cm2 (at 700 nm, only 15 to 20 % of the light penetrates until 3 mm deep)

*Examples :

• 50 nm diameter = 2ms TRT
• 100 nm diameter = 8 ms TRT
• 200nm diameter = 33ms TRT
• 400 nm diameter = 130 ms TRT

OPTIMIZATION OF THE CLINICAL RESULTS

The factors which interfere in hair removal optimisation are multiple :

- Wavelength : superficial and thin hair will respond better to short wavelengths (600 to 700 nm) and coarse and deep hair will respond better to longer wavelengths (700 to 800 nm). Therefore it is important to change laser when hair becomes thinner after three or four sessions with an Alexandrite laser (shift to Ruby laser or to Flash lamp?).

- Pulse duration time : thin and superficial hair do not need long duration pulses (5 to 20 ms), when deep and coarse hair need long pulses (40 to 100 ms).

- Fluence : the more energy is delivered by squared centimeter of ccutaneous surface, the more efficient is hair removal ; the art of the physician consists in finding the best compromise between efficacy and epidermal damages due to heat and absorption of melanin by the epidermis.

- Spot size: plus le diamètre du spot est important, plus l’énergie pénètre profondément, donc plus on a de chances de détruire le bulbe pileux, surtout si le poil est profond (maillot, aisselles, menton par exemple).

- Cooling of the epidermis : this factor is essential in performing a successfull laser hair removal. A cool epidermis does not burn, even with high fluences, except when not respecting the phototype or when treating recently tanned skins.

- Skin color : classical Fitzpatrick phototypes are not sufficient enough to appreciate the risk of burning the epidermis in laser hair removal. Th ethnic origin is at least so much important as the capacity of burning or tanning in the sun. Therefore, the new classification called « Skin Ethnic Color Types » seems more adequated to our work.

- Hair color : black and brown hair are the only ones to be possibly permanently destroyed by laser hair removal.Blond aand white hair can not be surely destroyed by laser in the actual state of the art.

- The particular case of tanned skins : it seems to us that a tanned skin definitely does not respond the same way as a black phototype skin under the laser beam or the flash lamp. Actually, we know that a sunburned cell protects itself by positioning melanin as a semicircular « hat » on the top of the nucleus ; this semi-cirular « hat » may be seen as a hair by the laser beam, which therefore destroys the cell.

We must not treat tanned skins, even with good reasons for it, even with low fluences, because it ends into epidermal burns.

A MISKNOWN FACTOR :
THE INTERVAL BETWEEN THE LASER SESSIONS

As far as we know, there is one factor of optimization of laser hair removal which has not been studied yet. And this is the interval between the laser sessions and the best rythm we can recomend to our patients in order to perform the best result in relation with the area we treat and with their own capacity to grow hair again on this specific area.

DEFINITION OF THE USUAL REGROWTH TIME (URT)

We performed a new method for the clinical evaluation of the hair cycle on a given area for a given patient : the definition of the Usual RegrowthTime. This seems to be directly linked to the theoretical hair cycle of the considered area

We evaluate at the first consultation with the patient the Usual Regrowth Time of the area we want to remove hair. We define it as follows :

Medium regrowth time on a given area in a given patient using previously any way of transitory hair removal, providing that this transitory method removes the totality of the hair on this area in one single session each time (waxing, shaving etc…).

Plucking and electric depilation for instance can not be considered because they do not take away the totality of the hair in one single session.

OUR RESULTS :OPEN STUDY ON 492 HAIR REMOVAL SESSIONS BETWEEEN JUNE 15 th 1998 AND 31st DECEMBER 2000.

MATERIAL :

• 278 sessions from june the 15th 1998 until december the 31st 1999
• 214 sessions from january the 1st until december the 31st 2000,
• 492 sessions in total
• After three years

Machine :

ALEXANDRITE 755nm long pulse LPIR 20 ms ( handpiece 7 or 10 mm, 1 impact/ second, fluence jusqu’à 40 joules / cm2

Centre : CENTRE LASER - 1, rue Duguesclin

86270 - LA ROCHE POSAY (France)

COMPUTER ASSISTANCE : « DERMATOBAZE »in 1998-99, then « 4th DIMENSION » Mac Intosh

METHODOLOGY :

Definition of the Usual Regrowth Time (URT) (see above)

Then we take the URT as a basic unit to compare the effficacy of every laser session ; we ask the patient to come back as soon as the hair regrowth is beginning (1 to 3 mm regrowth) ; (we shall see later that this URT is proportional to the hair cycle of the area).

The physician himself collects the datas and enters them in the computer.

Practical informations :

• Use of a cooling gel
• Delimitation of the treated areas with a red dermatological pen
• Shaving of the area the ame day or the day before
• Medium fluences between 17 and 24 joules / cm2
• Spot size : 10 mm

Selection of the patients :

Phototypes I to III ( we excluded the 3 cases of phototypes IV and V)

Black and brown hair ( we excluded blond and white hair).

Clinical evaluation

satisfaction of the patients : 80 %

immediate perifollicular œdema ( clinical sign of efficacy)

« burning sensation» during a few minutes or a few hours after the session ( less than 10% of the cases)

- crusts and hypopigmentation ( rare : 7 cases in total).

RESULTS AT DECEMBER 31st 1999 (6/15/98 - 12/31/99) :

	Sessions Number	Medium fluence	Medium impacts number	Usual Regrowth Time	% regrowth
1st session	106	21,02	356,15	1	50 à 70 %
2nd session	69	22,1	343,59	x 2,51	30 à 50 %
33rd session	46	22,7	397,97	x 4,55	5 à 20 %
More than 3 sessions	19	17,6	601, 31	x 5, 47	0 à 20%

Multiplication of the URT ( medium for 1999) :

• a) - After the first session : URT x 2,51
• b) - After the second session : URT x 4,55
• c) - After three sessions or more : URT x 5,47

RESULTS FROM January 1st to decembre 2000 :

	Sessions Number	Medium fluence	Medium impacts number	Usual Regrowth Time	% regrowth
1st session	59	21,51	606,58	1	50 à 70 %
2nd session	61	21,29	888,52	3,8	30 à 50 %
33rd session	46	22,3	940,59	7,6	5 à 20 %
More than 3 sessions	48	21,98	688,26	15,3	0 à 20%

Multiplication of the URT ( medium for 2000) :

• a) - After the first session : URT x 3,8
• b) - After the second session : URT x 7,6
• c) - After three sessions : URT x 15, 6

- So, a progression of approximately 4-8-16, which is close to the clinical impression of the physicians. (A certain amount of our « first sessions » for the year 2000 are most probably second sessions whose first session has been counted in the year 1999 because of the change of software meanwhile, which can explain the direct pass from 1 to 4 in this seriae).

The following graph shows the evolution of the Usual Regrowth Time according to our experience after three years.

OTHER MODIFICATIONS WERE OBSERVED :

Modifications of the diameter, the number et of the quality of regrown hair after each session (progressive transformation into vellus).

It seems that the elimination of the 100 % of the hair is impossible. It looks like the graph of the disminution of the number of hair tends towards but never reaches the zero (asymptotic graph).

DISCUSSION :

It seems to be an exponential graph which formula would be the following :

RT = URT x 2 at the power of n,

Where the variable n represents the number of sessions already performed

RT, the Regrowth Time since the previous session

URT the usual regrowth time, before the first laser session.

This hypothesis corresponds to the clinical impression we have and should be thoroughly looked at in a cliniccal study which methodology could be perfectable. This could may be allow us to understand better the enigm of the efficacy of laser hair removal whose principal advantage seems to be in the synchronisation of the hair cycles which allows a maximum permanent hair loss in a minimum number of laser sessions.

The evaluation of the URT and the use we make of it allows us to optimise the results. In our opinion, it looks totally non logical to give the same interval between the laser sessions for an upper lip or a leg hair removal when one knows that the hair cycle of the former is 4 months and the latter goes up to 20 months !

OUR HYPOTHESIS

A constant relationship exists between the URT and the hair cycle.

This relationship seems to be near 20, if we consider our own statistics.

We have given a questionnaire to some beauty institutes to objectivate these evaluations.

RELATIONSHIP WITH THE HAIR CYCLE

The hair cycles of the areas we commonly treat have been published in different papers (cf bibliography). We shall take some examples which show the constant relation existing between the hair cycle of the treated area and the Usual Regrowth Time we have defined for the same area. To simplify, if we compare the numbers for the upper lip and for the leg, we can observ that :

1) For the upper lip :

- the medium URT is around 5 days = 0,2 month
The medium hair cycle is approximately 4 months
Which gives the number : 20 ( 4 / 0,2 = 20)

2) For the leg :

The URT for the leg is approximately one month, when
The hair cycle of a leg is approximately 20 months (18_24 months)
Which gives the number : 20 ( 4 / 0,5 = 20) again.

This can lead to an ideal formula foor the ideal inerval between two hair removal laser sessions, which is in relation with the hair cycle of the treated area :

Ideal interval between two sessions = Espacement idéal entre deux séances = (HC / 20) x 2 at the power of n

Where :

HC is the hair cycle of the considered area.
n is the number of laser sessions already performed.

CONCLUSION

However, the evaluation of the URT with the patient remains a better method, according to our experience, because it integrates the individual variations of the hair cycle.

We hope that new teams of hair removal laserists can experiment this method which is simple and based on the clinical observation and a good collaboration with the patients, in order to understand better and optimise the results of laser hair removal.

BIBLIOGRAPHY

a. Pierre Agache et al. , Physiologie de la peau et explorations fonctionnelles cutanées, éditions E M inter, explorations fonctionnelles humaines ; juillet 2000

b. Adeline de Ramecourt, Epilation électrique, sous la direction de J.J. Legrand, Editions Arnette - Paris - ISBN : 2-7184-0705-0

c. D.Van Neste, JM Lachapelle, JL Antoine, Trends in human Hair growth and Alopecia research, Edité par Kluwer Academic publishers, London

d. Tina Alster, Manual of cutaneaous laser techniques, Lippincott Williams & Wilkins, Wolsters Kluwers company, second edition

Comparative table of the medium hair cycles from different zones and the different Usual Regrowth Time of the same zones

Considered area	Hair cycle (HC) (medium - days)	Usual Regrowth Time ( URT) (medium -days)	HC/URT(medium-days)
Upper lip	4 à 5 months 120 à 150 d (135 d)	6 à 15 d (10,5 d)	20 à 10 (15 )
Chin	15 months (450 d)	15 à 20 d (17,5 d)	22, 5 à 30 (26)
Axillae	18 months(540 d)	15 d	36
Bikini	18 months (540 d)	15 d	36
Thighs	16 months (480 d)	30 d	16
Legs	16 months (480 d)	30 d	16
Arm	9 months (180)	15 d	12
MEDIUM	-	-	22, 4

NAME OF THE INSTITUTE :

AGE :
�Less than20	�20 à 30 yrs	�30 à 40 yrs	�40à 50 yrs	�50 à 60 yrs	�Plus de 60 yrs
Waxing since… Upper lip :
�Less than 5	�5 à 10 yrs	�10 à 15 yrs	�15 à 20 yrs	�20 à 25 yrs	�Plus de 25 yrs
chin :
�Less than 5	�5 à 10 yrs	�10 à 15 yrs	�15 à 20 yrs	�20 à 25 yrs	�Plus de 25 yrs
axillae :
�Less than 5	�5 à 10 yrs	�10 à 15 yrs	�15 à 20 yrs	�20 à 25 yrs	�Plus de 25 yrs
bikini :
�Less than 5	�5 à 10 yrs	�10 à 15 yrs	�15 à 20 yrs	�20 à 25 yrs	�Plus de 25 yrs
thighs :
�Less than 5	�5 à 10 yrs	�10 à 15 yrs	�15 à 20 yrs	�20 à 25 yrs	�Plus de 25 yrs
legs :
�Less than 5	�5 à 10 yrs	�10 à 15 yrs	�15 à 20 yrs	�20 à 25 yrs	�Plus de 25 yrs
skin color:
�Deep white	�Medium white	�Medium brown	�Brown	�Asiatic	�African
hair color:
�White	�Blonds	�Medium brown	�Deep brown	�Black
hair diameter:
�Coarse hair	�Thick hair	�Medium	�Thin	�Very thin	�Vellus
sunburns (With à european sun ) :
�Always	�Frequently	�Scarcely	�Very scarcely	�Exceptionally	�Never