Amber Bhargava
Beauty and the Geek:
The Engineering Behind Laser Hair Removal
Understanding laser hair removal requires knowledge of many disciplines. Quantum and
optical physics, the biology behind the growth cycles of hair, and the historical and modern
rationale for depilation (hair removal) contribute to this interesting cosmetic procedure. The
study of Laser Hair Removal reveals the interconnection between societal values and science
while also providing an interesting vantage point from which to view engineering as a part of
beauty culture.
[1. Youtube clip of laser hair removal commercial]
http://www.youtube.com/watch?v=rSUq7yhHJzc&feature=related
Introduction
Engineers must consider the unintended consequences of their actions. Smart robots could
take over the world; the promotion of a new source of energy could cause riots in Mexico -- the
discovery of hydrogen spectra could create a 244 million-dollar cosmetic industry [1]. While the
robot revolution has yet to come, the unmitigated disaster of corn-based ethanol [2] still haunts
the alternative energy world and a cosmetic industry based on the atomic spectrum has flourished
in America. That industry happens to be laser hair removal. In 2009, 60% of adults age 18-26
responded that they want to get laser hair removal, and more than 1.2 million laser hair removal
procedures occurred in 2010. [1] The allure of laser hair removal is understandable: the
procedure is billed as “virtually painless, safe and long lasting,” and a high-tech halo still
surrounds laser technology.
It is important – as with any medical procedure - to understand how laser hair removal works,
to evaluate the science on its own merits and weigh the potential side effects. However, this is
not a simple task; the engineering behind laser hair removal incorporates a wide range of
disciplines from quantum mechanics to biology to the elusive science that is human attraction.
The History of Hair Removal
Humans have been removing hair since – and possibly before – the ancient civilizations of
Egypt. Both men and women in Ancient Egypt shaved the hair from their body and head, for
dual reasons of cleanliness and fashion. Lice were a frequent problem and it may have been
difficult to keep hair clean in the hot Egyptian climate; additionally, wigs were seen as both
fashionable and cleaner than natural hair. [3] The Ancient Egyptians waxed off hair using
caramelized sugar and shaved using the precursor to the straight razor, shown in Figure 2.
[2. Image: Egyptian Razor]
http://www.egyptancient.net/images/rasoio.gif
Hair removal remained important as a sign of civilization and social status. Roman soldiers –
who shaved their heads to prevent hair-pulling in battle – coined the term ‘barbarian’ in
reference to the un-barbered enemy.
Although it is relatively easy to keep hair clean today, hairlessness continues to be important
as a cultural phenomenon. Skin is considered ‘flawless’ if it is without acne, blemishes, and hair.
This is especially true for women in America, where popular magazines and websites often
publish articles with titles like “See Hairy Celebrity Slips: Armpits, Legs, Guess Who?” [4]
These articles emphasize that it is socially unacceptable to have body hair. This social message
created the impetus to invest in new hair-removing technologies.
Advanced technologies included the invention of the modern razor by K. C. Gillette in the
late nineteenth century [5]. More futuristic methods include electrolysis, in which an electric
current is applied to the hair follicle. This method – not laser hair removal - is the only method
approved by the FDA to permanently remove hair.
Lasers have always captured the public imagination, and laser hair removal was attempted
almost as soon as lasers were invented. These early lasers were impractical and often caused
skin damage due to ineffective hair targeting and lack of control over the power of the laser. It
took forty years - from the invention of the laser in 1957 to 1997 – for scientists and
dermatologists to engineer a practical laser hair removal system.
The Biology of Human Hair
Human hair is made out of three parts, the medulla, cortex, and cuticle, as shown in Figure 3.
The medulla makes up the center of the hair, the cortex surrounds the medulla and is made out of
roughly straight keratin structures, and the cuticle is the outside of the hair, made up of flat cells
laid out like roof shingles. [6] The hair itself is part of a biological system that includes the
follicle, where the hair grows, the sebaceous gland, which when infected produces pimples, and
the arrector pili muscle, which causes goosebumps.
[3. Diagram of the structure of the hair]
http://www.hshairclinic.co.uk/_images/hair_structure.jpg
Two types of melanin, eumelanin and phomelanin, contribute to the pigment of human hair.
Eumelanin colors dark hair, while phomelanin contributes to red hair. The melanin in hair is a
chromophore – the part of a molecule responsible for its color. [7] Color, in human hair and in
general, is caused by the absorption of certain wavelengths of light and the reflection or
transmission of others. This property is what allows laser light to be absorbed selectively by hair
and not the surrounding skin. However, to know exactly why this happens, you have to go back
to quantum physics.
The Physics behind Laser Technology
In 1913, Neils Bohr postulated that electrons in atoms could only have discrete (quantized)
orbits and energies. [8] He stated that electrons could jump from one orbit to another by emitting
or absorbing energy in amounts predetermined by the orbits themselves. Bohr proved his theory
by discovering the atomic spectrum of the Hydrogen atom, which contains one electron. When
the electron lost energy, it would emit a wavelength of light corresponding to the change in
energy between the orbits. The emitted wavelength of light –if in the visible band - would
correspond to a specific color. Although Bohr was not completely correct in his assessment of
atomic structure, the concept of discrete spectra allowed the development of lasers.
What is a Laser?
The term laser is an acronym for Light Amplification by Stimulated Emission of Radiation. In
the most basic sense, the laser is a device that emits light of a specific wavelength. Charles
Townes and Arthur Schawlow invented the modern laser in 1957. At the time, Townes had
previously discovered a method of amplifying electromagnetic waves– however, he had used
microwave radiation instead of visible or infrared radiation. [9] The theory behind lasers –
exciting atoms in pure gases or solids to produce specific wavelengths of light – had been known
for years, but Schawlow put the theory into practice. The first laser was comprised of a long
narrow cavity containing the desired atoms with silvered mirrors at each end. The reflected light
rays caused more atoms to be energized and consequently radiate energy at the specific
wavelength.
At the center of a modern laser is the Gain Medium, a material through which specific
wavelengths of light can be amplified. The other essential parts of the laser include a mechanism
to apply energy to the Gain Medium, and reflector or other way to provide optical feedback.
energy is applied to the Gain Medium, the electrons in the medium are excited to a higher
orbital, then fall to a lower orbital, emitting light as a byproduct. The purity of the Gain Medium
affects the purity of the spectrum emitted. A high quality laser should emit a very narrow
spectrum. [10] This narrow spectrum is characterized graphically in Figure 4, which shows that
the spectrum of a helium-neon laser is confined to a small range of frequencies centered around
632 nanometers.
[4. Image: Spectrum of a Helium Neon Laser]
http://en.wikipedia.org/wiki/File:Helium_neon_laser_spectrum.svg
How Laser Hair Removal Works
In Laser Hair Removal, the laser light is applied to the entire area over which a person wants
to lose hair – the hairs are not individually ‘zapped’ by the laser (unlike electrolysis). By not
zapping individual hairs the process is much faster than electrolysis; however, the laser light may
harm the skin if not applied correctly. [11] As shown in Figure 5, the laser hair removal patient is
prepped for their treatment by cutting the hair short and applying a cooling gel to the skin to
reduce the chance of overheating; then, the laser light is applied to the skin.
[5. Image: How Laser Hair Removal Works]
http://laserremovalreviews.com/wp-content/uploads/2012/07/laser-hair-removal-process.jpg
Laser hair removal works by targeting areas with specific chromophores - in this case, the
melanin found in the hair (See previous section for a description of chromophores). The laser
emits a wavelength of light that should be primarily absorbed by the hair and primarily reflected
by skin, causing the hair follicle to heat up faster than the surrounding skin. This causes
inflammation, which will kill the follicle that produces the hair. However, you shouldn’t expect
to go in for a treatment and come out hairless – it can take up to three weeks for the affected
follicles to shed the treated hair.
No single laser works on the complete range of skin and hair types (skin color is less relevant
than melanin content), since the laser hair removal system works based upon a difference
between skin and hair color in order for the hair to absorb the light without burning the skin.
Melanin under the skin – even if inactivated, will absorb rather than reflect light at the same rate
as melanin of the same type in the hair. If the skin and hair absorb the light at the same rate, the
laser will not be able to ‘target’ the hair. For this reason, for many years laser hair removal was
only possible for people with light skin and dark hair. However, new lasers have been invented
that work for different skin and hair combinations. For example, the alexandrite laser with a
relatively short wavelength (775 nanometers) is effective on patients with lighter skin, although
it is dangerous for patients with dark skin, while the neodymium-doped yttrium aluminum garnet
laser was developed to have a longer wavelength (1064 nanometers) that works well on darkerskinned patients. [12]
Although scientists have made advances in the selection of laser gain medium, there are still
many other factors that have to be considered in the process of creating a safe and effective laser
hair removal system. These parameters include the pulse width, the width of the laser beam, and
the energy of the laser light. A shorter pulse width with higher energy and a wider laser beam has
been shown to be more effective at disabling hair growth but also runs the risk of collateral skin
damage.
Even if scientists engineered a laser that was perfectly absorbed by hair and perfectly
reflected by skin, patients would still have to make several treatments to become hairless in the
desired region. There are three phases of hair growth: anagen, catagen, and telogen, in which
follicles are either active or dormant. Laser hair removal only works on active, growing hair
follicles, since that is the time when the follicle is most sensitive. (At this point in the hair growth
cycle, the early Anagen stage, the hair is completely under the skin.) In order to have a high
probability of treating most hair follicles at the time they are active, dermatologists suggest seven
treatments spaced anywhere from three to eight weeks apart. [13]
Dangers of Laser Hair Removal
Laser hair removal - marketed as permanent and painless – was not well understood or well
engineered for the first four decades of its development. The first laser hair removal systems in
the 1960s were not only impractical, but also harmful to patients, damaging the skin more than
the hair. Side effects included itching, redness, acne, hypo or hyper-pigmentation, and burning of
the skin similar to sunburn. [10] However, laser hair removal continued to grow in popularity;
patients volunteered as test subjects for clinical trials. [14] Today, the science of laser hair
removal is much older and better understood, although side effects continue to be a problem for
laser hair removal clinics and injuries can still occur if technicians are not trained or systems are
improperly calibrated.
In 1995, the company ThermoLase created the first laser for hair removal approved by the
FDA; however, four years later patients won a class action lawsuit against the company for false
advertising. ThermoLase clients were angered when the laser hair removal they received was not
permanent – many clients experienced “full regrowth of all hair.” [14] Although the technologies
have improved, laser hair removal does not guarantee permanent results or complete elimination
of hair – even with multiple treatments. Today, laser hair removal companies are careful to
market their product as a ‘reduction’ in hair growth, and regard successful treatments as ones that
have reduced the thickness or quantity of hair.
Physics, Culture and Laser Hair Removal
The cosmetic procedure of laser hair removal has probably made a small impact in the lives
of today’s physicists – the intellectual successors of the scientists and engineers who discovered
the theories and technologies that make laser hair removal possible. However, laser hair removal
has – unintentionally – helped to shape the study of optical physics. The use of lasers in medical
applications continues to grow, from minimally invasive surgeries to LASIK to laser fat removal
[15]. The laser hair removal industry’s funding and interest in the science of lasers in biological
applications contributed at least a small part to these discoveries.
In the end, society decides what scientific research survives, which projects receive funding
and which fade into obscurity. In order to be successful, engineers must create things that make
life easier, things that people desire. The continuing story of laser hair removal shows us that
people want the same thing they desired thousands of years ago – to conform to a standard of
beauty that few can achieve without the help of the unintended consequences of physics.
References:
[1] (2012, Sept. 5). Laser Hair Removal Statistics. The Hair Removal Journal. [Online].
Available: http://www.statisticbrain.com/laser-hair-removal-statistics/
[2] M. Lagi. (2012, May). Impact of Ethanol Conversion and Speculation on Mexico Corn
Imports. New England Complex Systems Institute. [Online]. Available:
http://necsi.edu/research/social/foodprices/mexico/
[3] (2012, Sept 12). Egyptian Beauty Secrets: Article Two. Tour Egypt. [Online] Available:
http://www.touregypt.net/egypt-info/magazine-mag07012000-mag4.htm
[4] N. Torres. (2012). See Hairy Celebrity Slips: Armpits, Legs, Guess Who? About.com.
[Online]. Available: http://hairremoval.about.com/od/waxing/ss/celebrity-slips_2.htm
[5] R.B. Adams. (1978). King C. Gillette: The Man and His Wonderful Shaving Device. [Online]
Available: http://web.mit.edu/invent/iow/gillette.html
[6] M. Feughelman. “The Morphology of Wools and Hairs” in Mechanical Properties and
Structure of Alpha-Keratin Fibres: Wool, Human Hair and Related Fibres. Sydney,
Australia: University of New South Wales Press, 1996.
[7] (2012 Sept. 16). Chromophore. Wikipedia. [Online]. Available:
http://en.wikipedia.org/wiki/Chromophore
[8] D. P. Ketumahkha. (2004 May 24). The Bohr Atom. [Online] Available:
http://venables.asu.edu/quant/Dinesh/Bohratom2.html
[9] American Institute of Physics. (2012). Bright Idea: The First Lasers. [Online] Available:
http://www.aip.org/history/exhibits/laser/sections/whoinvented.html
[10] Lawrence Livermore National Laboratory (2012 Sept. 13). Education: How Lasers Work,
NIF & Photon Science. [Online] Available:
https://lasers.llnl.gov/education/how_lasers_work.php
[11] Mayo Clinic (2012). Laser Hair Removal. [Online]. Available:
http://www.mayoclinic.com/health/laser-hair-removal/MY00134/
[12] (2012 Sept. 16). Laser Hair Removal. Wikipedia. [Online]. Available:
http://en.wikipedia.org/wiki/Laser_hair_removal
[13] A. Thompson. (2011). Understanding Pulsed Light Hair Removal. [Online]. Available:
http://www.ajthompson.com.au/human-sciences/understanding-pulsed-light-hairremoval.htm
[14] A. James. (2001 August 21). Hair Removal methods: Laser History and Current Issues.
[Online]. Available:
http://www.quackwatch.com/01QuackeryRelatedTopics/Hair/laserhistory.html
[15] (2012 Sept.) Education: Photochemistry. Zerona. [Online]. Available:
http://www.myzerona.com/education-photochemistry-0