Deka Laser Systems provide a fast and reliable solution for the removal of facial hair and for laser depilation in general
LASER HAIR REMOVAL: Equipments and Systems
Laser hair removal has rightly been brought to the attention of those who work in the sector for its undeniable advantages with respect to the usual techniques: greater reliability and lower occurrence of side effects. The piliferous follicles are found below the base layer of the epidermis, sometimes at a depth of up to 7mm, so the fundamental characteristics of each hair removal laser should be the transparency of the skin and the selective affinity with the components of the hair, especially melanin. Also, the physiology of the hair has not yet been completely understood due to the length of time necessary for these studies.
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Existing studies have shown that the hairs go through different sequential and cyclical phases: each cycle involves an anagen phase during which the hair grows and the telogen phase during which there is no growth. A further time between the anagen and telogen phases is called catagen, which lasts for approximately 2-3 weeks.
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The times of the various phases have been studied at length with respect to variables such as the different areas of the medium, sex, age, season, etc. In each individual it is presumed that there is a variation of about 10% in the duration relative to the various phases. Moreover, it has been demonstrated that the percentage of hairs in the telogen phase increases gradually with age. The phases of the hairs are absolutely asynchronous on large surfaces with the result that the human body always has a light covering of hair. The hair removal treatment is more or less effective depending on the damage caused to the follicular structures. When razors or hair removal creams are used no damage is done to the germinative parts of the hair. These parts are partially damaged, in a mechanical way, when using tweezers or wax for hair removal.
Only electrolysis, thermolysis, X-rays and lasers have shown to be capable of effectively destroying the deep follicular areas. If these areas are not damaged in any way, as they are with wax, the anagen hairs will continue to grow at a speed of about 0.2mm per day and will appear on the skin after a period of time that will depend on the depth of the follicle and on how large a portion of the hair shaft has been removed. If, however, the percentage of the hairs in the telogen phase is high (let’s say 50%) only those in the anagen phase will grow back, giving the impression that a significant removal has been obtained. This is due to the fact that the removal of hairs is certainly greater than 50% also considering those in the catagen phase. Moreover, average follicular damage can induce an anagen hair to pass prematurely into the telogen phase, before starting to grow again after a certain period of time. Significant perifollicular damage is obtained when at least one or all the generative structures of the hair are partially or completely destroyed.
Perifollicular fibrosis, induced through treatment, can also delay the re-growth of the piliferous structures in the case of partial damage; in this case the hair grows back smaller and lighter. There can also be a relative effect using thermolysis or laser treatment, the hair can be white, deep or the skin not sufficiently transparent to the wavelength used, with the result that not all the anagen hairs are destroyed. Besides this, it seems that the telogen hairs are affected to an irrelevant degree with respect to the anagen hairs.
In the following paragraphs we will analyze more deeply these details that will indicate the most suitable laser for the hair removal. In this way we will discover that Nd:YAG long-pulsed lasers provide advantages that other systems do not have. This is particularly true for darker skins which make up the absolute majority in countries of Latin origin. We will also see how the right energy and flow are capable of creating an ideal combination in order to obtain an effective and safe hair removal treatment.
During the last few decades numerous methods for hair removal, even temporary, have been developed. At different times, more or less valid methods have been introduced, such as shaving, waxing and the use of tweezers, which turn out simply to be temporary solutions. The only non-laser system capable of damaging the hair in a definitive way is through electrical depilation, in both versions: continuous and alternating current. But electrical hair removal has considerable disadvantages: it is extremely tedious and long and involves certain risks that can cause scars.
Numerous factors are involved in obtaining adequate results from hair removal: this depends on the physiology of the hair cycle, as yet not completely understood, the physical qualities of the tissue, the type of equipment used, the experience of the doctor and particularly the expectations of the patient. Laser hair removal has made great steps forward but, to make a conscious choice, it is necessary to know all the differences that the various types of laser can have. In the figure above we can see the anatomic structure of the hair. In order to obtain its definitive destruction it has been shown that it is necessary to destroy the third inferior part of the follicle, the area around the bulb and the external part of the root. By definitive destruction we mean, in the case where a laser is used, bringing these areas to such a temperature that their biological functions are irremediably jeopardized (photo-coagulation).
In order to reach the quantity of energy required to photo-coagulate the deepest follicles (up to 7mm) or those with the lowest melanin content, it is necessary to provide a greater quantity of energy directly from the laser. If less penetrating wavelengths are used, such as the ruby laser (694nm, red in the figure on the side), the alexandrite laser (755µm) or the diode laser (810µm), a lot of energy must be used in order to have enough of it in depth, with a serious risk of damaging the epidermis. These wavelengths, despite having a high affinity with melanin, become dangerous as the skin darkens due to the competition between the melanin in the skin and that in the hair.
The considerations regarding the use of large diameter spots in order to increase the depth of these lasers are interesting from a theoretical point of view but clash with experimental measures. Z. Zhao and P. Fairchild have directly measured the depth of penetration into the skin and have shown, in "Dependence of Light Transmission Through Human Skin on Incident Beam Diameter at Different Wavelengths", SPIE Proceeding, Vol. 3254, 01.98, two important aspects concerning the increase in the size of the diameter of the laser beam.
The first is that even increasing the diameter over a certain size the laser beam does not reach the deepest areas (for example, for the ruby laser and the alexandrite laser this saturation is obtained at 10mm with white skin). Moreover, the depth of these wavelengths, at 10mm, is the equivalent of that of the Nd:YAG laser at 7mm. For dark skins the equivalence for 10mm is 5mm of the Nd:YAG laser.
The fundamental characteristic of photo-depilation can be found therefore in the numerical relation between the melanin concentration in the skin and in the hair. This relation is very important in evaluating the effectiveness and the safety of the laser treatment but above all in evaluating which the best sources to use are. The ratio between the temperature of the piliferous bulb and the epidermis can be calculated, in the case of shorter pulses, by the thermic relaxation time, that is the time in which the thermic diffusion from the hair becomes significant.
In this case, for hair colours 10 times darker than the epidermis (very dark skin and black hair), the ratio of the temperatures is shown in the following figure on the left according to different depths. The same calculation is carried out in the case where the relation of colour is only equal to 5 (hairs only slightly darker than the epidermis) shown in the following figure on the right. The following table shows the temperatures that the epidermis reaches in the two cases, for a final temperature of the piliferous bulb of 100°C.
Importance of the pulse length
Since it is preferable to treat the follicle in a selective way without damaging the surrounding tissue, the energy needs to be released in pulses of a length that is less than or equal to the thermic relaxation time of the target structure. The thermic relaxation time (TRT) is the time it takes for the structure that has absorbed the laser radiation, and is therefore at a certain temperature, to lose 50% of the heat stored. In order to destroy the follicle it is necessary for the pulse duration to be about the same as its TRT. Pulses with a longer duration would only have the effect of heating the follicle at lower temperatures because it would have time to cool down in the meantime. Since the epidermis is the first to be exposed to the laser beam, it is extremely likely to be damaged by the energy of the laser pulse if the duration is shorter than its TRT.
Therefore, in order to hit the follicle the laser energy must be released in a pulse whose duration is longer than the TRT of the epidermis (estimated at a few milliseconds) and shorter or the same as the TRT of the follicle (a few tens of milliseconds).
The long impulse Nd:YAG laser provides all these characteristics: considerable penetration wavelength (1064 nm), sufficient energy to damage the follicle and duration necessary to protect the skin. Many laser systems with wavelengths lower than 1064nm give a strong cooling of the skin in order to limit possible damage to the superficial layers. There are many suggested methods: sprays, cooled windows, cold gels and air.
The first method mentioned above consists in spraying a certain quantity of the spray on the skin before the laser pulse. This method offers numerous disadvantages. First of all the quantity of spray given must be calibrated for each different area treated and for every patient with the risk of either not protecting sufficiently or causing burns through excessive cooling. Another disadvantage is the formation of frost on the skin which causes an increase in the radiation reflected back and a change in the optical properties of the part of skin cooled down.
The cooled window method is not very effective because the thermal conductivity is low and difficult to calibrate manually. Moreover, the window easily condenses the steam in the environment creating a layer of water that is all the more reflecting. The spreading of cooling gel on the skin and the use of cool air are less expensive methods and free from problems, with preference given to cool air because it is optically transparent and more efficient.
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