Principles of Laser Hair Removal.

This article is for those who are interested in the technical details of Laser Hair Removal.

Laser hair removal depends on the principle called ‘Selective Photothermolysis’. Basically, hair being black, absorbs more of the laser energy, and gets heated up and destroyed.

This absorption depends on the color characteristic. Particular colors absorb particular wavelengths, for example, a red colored object absorbs all wavelengths except the red wavelengths which are reflected back. Black colored objects absorb all wavelengths. The colored part of the objects which absorb laser light is called chromophore. In the body, there are two main pigments or chromophores which we are interested in — red hemoglobin and black melanin. In hair removal, we want a light which is preferentially absorbed by black melanin and not absorbed by red hemoglobin.

Melanin is the pigment which gives color to our hair and skin. There are in fact three types of melanin — black eumelanin, brown eumelanin and pink pheomelanin. Black eumalanin alone colors hair black and brown eumelanin alone colors it blonde. A mixture of black and brown eumelanin is the most common and different proportions gives different colors to our hair ranging from jet black to brown. Pheomelanin gives a pink color to our lips, nipples, glans penis and vagina. A mix of pheomelanin and brown eumelanin gives red hair.

Another type of melanin is neuromelanin which is found in the brain.

In the hair, the melanocytes are found in the hair bulb. These melanocytes produce melanin continuously during the anagen growing phase of the hair. This melanin is injected into the keratin cells which form the keratin of the hair thus coloring the hair. Hence the whole hair from the shaft to the bulb is colored by melanin.

Melanin is also present in the skin. It is present in the basal layer of the epidermis. The epidermis is the outermost layer of the skin and is just 0.1 mm in thickness, about the thickness of a sheet of paper. The basal layer of the epidermis contains melanocytes, which forms melanin which gets distributed in all cells of this layer. Below this is the dermis, the main layer of the skin which can be between 1.5 and 4 mm in thickness.

The hair follicle extends upto 4 mm in depth into the skin. The germinal cells of the hair, from which the hair is formed, lies at a depth of about 1.6 mm in the skin.

When laser light falls on the skin, the melanin of both the skin and hair absorbs this energy. In the hair, it is the shaft of the hair which contains melanin and heats up. As the hair shaft gets heated, it damages the germinal cells which surrounds the shaft, and this leads to obliteration of the hair.

Both skin and hair melanin absorbs laser heat energy, but in fair skin such as Europeans and Americans, very little energy is absorbed by the skin and so this is not a problem. In dark skin as in Indians, the skin absorbs more energy.

The reasons damage occurs to hair and not the skin are:

1. Hair contains much more melanin than skin. Black hairs absorb much more energy than the skin. This is the main reason why hair gets preferentially destroyed. Black hairs as in Indians are thus the best candidate for Laser Hair Removal. Light hairs such as blonde or brown hairs are not so easily damaged and white hairs are not damaged at all.

2. Different depths of hair and epidermis. The melanin containing layer of the epidermis is very superficial, while hair lies at a greater depth. Longer wavelengths of light penetrate deeper and spare the superficial layers, and this leads to much less damage in the skin.

3. TRT or thermal relaxation time. This is the time which a body takes to lose heat. Skin has a much larger surface area than the hair shaft, which means that it cools down much faster. The hair shaft retains heat much longer. This is taken advantage of through two techniques — by increasing the pulse width in the stamp technique and through the low fluence multiple pass technique.

There are various characteristics of the laser light and skin and which interact in this and affect how the absorption of laser energy takes place. The wavelengths between 600 and 1100 nm are preferentially absorbed by melanin, and so we want lasers which emit light within this wavelength.

Longer wavelengths penetrate deeper into the skin leaving the melanin in the skin untouched and affecting the melanin of the hairs. But on the other hand, the longer the wavelength, the lesser is the absorption, and short wavelengths are absorbed more. So Nd-YAG lasers which have the longest wavelength are the safest for dark skin, but their effectiveness is also less requiring more number of treatments. The Ruby laser on the other hand, is most effective but also has the potential for skin damage. The diode laser falls in the middle of this range, and hence is considered the most useful.

Hair color is most important, as already discussed, and also hair thickness, density,etc.

Skin color of course is important, at the same time skin moisture, softness and smoothness all affect the laser interaction.

Skin color is divided into six types based on the Fitzpatrick scale:

Fitzpatrick classification of skin types.

Type I Always burns, never tans
Type II Always burns, sometimes tans
Type III Sometimes burns, always tans
Type IV Rarely burns, always tans
Type V Moderately pigmented
Type VI Black skin

Most Indians fall into Type 4, a few fairest ones fall into type 3 and a few in type 5. But in general it can be assumed that all Indians, specially in the North East, are in type 4.

Four main types of laser have been used for laser hair removal:

Ruby laser: Its wavelength is 694.3nm. It is very well absorbed by melanin. However it is not found suitable for darker skin.

Alexandrite laser: Alexandrite laser was one of the most commonly used lasers till the diode was discovered. Its wavelength is 755 nm. It is well absorbed by melanin and is also suitable for dark skin.

Diode laser: Diode laser has emerged as the gold standard of laser hair removal. Its wavelength is 810 nm. As such it falls in the middle of the range, being well absorbed by melanin of the hair and still having waves which are long enough to spare the epidermal layer of the skin.

Nd-YAG laser: This has a long wavelength, of 1064 nm. Because of this it spares the skin to the highest degree. But at the same time, its absorption is also much less and so a larger number of treatment sessions are needed with this. It is most suitable for Skin types 5 and 6 and not necessary for the Indian skin type.

Besides the type of laser, there are a number of parameters on the laser machine which need to be manipulated to get optimal results.

Parameters of laser machine

There are three main parameters in the laser machine which are adjusted according to the type of hair and skin:

Fluence: Fluence is the power of the laser light. Just we can adjust the brightness of some lights, the power of the laser can also be adjusted and this unit is called Fluence. The higher is the Fluence, the more is the power of the laser and hence more hairs will get destroyed. But the power cannot simply be made very high, as part of the laser light will also be absorbed by the skin, and so raising the power indefinitely will also tend to cause skin complications.

Pulse width: Pulse width is the length of time for which the laser is 'on'. Increasing the pulse width will give more energy to the skin and thus destroy more hair. But just as in fluence,we cannot simply increase the pulse width as skin may get damaged. Unit for pulse length is msec.

Rate: Rate is the number of times in a second for which the laser fires. It can fire once a second, two times a second and so on. The more the rate, the more the energy delivered to the skin if the laser is trained on the same spot. Rate is usually adjusted according to the technique the operator is using and how fast he or she is moving on the skin. Unit is denoted as n.

These three parameters are adjusted according to the skin and hair type. Increase in any of these three parameters will increase the energy delivered to the skin and thus destroy more hair, but at the same time chances of damage to the skin is also more. Hence adjustments have to be made for this. In fair skin, a high fluence is administered to destroy more hairs and the pulse length is kept small to minimize pain and skin damage. In dark skin however, such high fluence cannot be administered because of chances of skin damage. However, it is noticed that pulse length can be increased to compensate as increasing pulse length does not cause much skin damage. So in dark skin, lesser fluence with longer pulse length (msec) is administered to achieve the same effect. Pulse rate, n, is adjusted according to the operator's comfort.

Another very important part of the Diode Laser machine for hair removal is the cooling device. Cooling of the tip of the laser applicator is essential to minimize skin damage, and also pain and discomfort. Various types of cooling devices like cold air, cryo techniques, etc have been used in lasers. The most modern technique is to use a sapphire cooling device. This is also the technique used in the laser in our clinic.

Arogyam Hair Transplant and Cosmetic Surgery Center uses the best and most modern machine, the Diode Laser machine, for safe and permanent removal of hair at a competitive price, in Guwahati, Assam and entire North East.

Techniques of laser hair removal:

There are two main techniques used by the operator during Laser Hair Removal.

Stamp Technique:

Here the laser emitting window, which is a small square window, through which the laser spot is emitted, is placed on the skin in a stamping method, like using a rubber stamp on paper, and the whole area is covered. It is the most common technique used. The main parameters to be adjusted are Fluence, the power of the laser light, and pulse width, or the time for which the laser is on. For fair skin, a high fluence is used to cause adequate hair damage, and to compensate for this to avoid skin damage, a low pulse width is used, for example, Fluence can be from 25 to 40 and pulse width around 10-20. But for dark skin, such high fluence cannot be used as it may cause damage to the skin. So Fluence has to be lowered. But it has been found that pulse width in turn can be increased, and this will not cause harm to the skin as the skin cools off quickly. So in dark skin as in Indian skin types, fluence is kept low, from 10-15, and pulse width is increased, from 30 to 60. This ensures selective harm to the hair follicles while skin remains unharmed.

Low Fluence Multiple Pass Continuous Motion technique:

This is a recent technique which has proved to be a big boon for dark skin. This takes advantage of the fact that skin cools off quicker than the hair follicle due to its larger surface area. It allows for high heat build up in the hair with low fluence, so that there is no harm to the skin at all. Here the operator uses the hand piece in continuous motion, as in ironing clothes, without stopping at any point. As an area is touched, both the skin and hair follicle heats up, but as there is a small gap till the next pass of the laser, the skin cools down in the meantime while the follicle retains some heat. At the next pass the follicle acquires more heat while the skin cools down again till the third pass and so on. As this continues, a very high heat builds up in the hair follicle while the skin remains at normal temperature. This allows us to heat up the hair with a very low fluence, thus ensuring that there is no harm at all to the skin while destroying the hair follicle more effectively. Here fluence is kept low, from 10-15 and pulse width around 20 msec, and rate from 5-10. Multiple pass technique is very useful for both fair and dark skin, but is a special boon for dark skin as very effective hair removal can be done while still being very safe for the skin.

Advantages of multiple pass technique are:

1. Much less pain and discomfort
2. Much more effective destruction of hair
3. Much less skin complications.

Multiple pass technique is used in Arogyam Laser Hair Removal. Stamp technique is also very important in some areas like the lip, near the eyes and in pubic area where surrounding areas need to be guarded carefully.

Arogyam Hair Transplant and Cosmetic Surgery Center uses the best and most modern machine, the Diode Laser machine, for safe and permanent removal of hair at a competitive price, in Guwahati, Assam and entire North East.

Dr. P. J. Mazumdar.
Arogyam Hair and Cosmetic Surgery Clinic

Located at
G.S. road, Rukminigaon,
About 50 meters from Downtown Hospital towards 6 Mile.
Opp. HDFC Bank, Reliance Trendz and Hotel Shoolin.
Next to Petrol Pump

Phone: 07637089211.

To know about the exact cost and other information, and for appointment, SMS or call directly at ⇒ +91 7637089211 between 10 AM and 4 PM on all weekdays from Monday to Saturday.

or email at ⇒ email

Consultation hours:

Arogyam Multispecialty Health Clinic:
From 2 PM to 7 PM every weekday except Sunday.
Arogyam Multispecialty Health Clinic
Rukminigaon, G. S. Road, About 50 meters from Downtown Hospital towards 6 Mile.
Opp. HDFC Bank, Reliance Trendz and Hotel Shoolin.
Next to Petrol Pump Phone:
+91 7637089211

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The academic certificates of Dr. P. J. Mazumdar may be examined here: Academic Certificates. His resume can be perused here: Resume. To find the contact address and other details, go to Contact.

By Palash Mazumdar