Red light delivered by
low intensity lasers, has been used to stimulate tissue repair for
over 30 years. Its uses now include the alleviation of a range of skin
conditions including
Acne (Hirsch and Shalita, 2003)
Scarring (Patel and Clement 2002)
Skin deterioration due to aging and sun damage (Alam & Dover,
2003)
All these conditions involve tissue injury, sometimes acquired over
many years. Their improvement is achieved by tissue repair, which can
be initiated and stimulated by exposure to low intensities of red
light and to some other forms of electromagnetic radiation such as
infrared (IR) radiation. Exposure to red light increases blood flow to
the skin thus improving its metabolism, and stimulates the manufacture
of collagen, the protein that gives strength to the skin (Bjerring et
al 2002). Other uses of red light include accelerating the resolution
of inflammation (Dyson 2004) and the reduction of pain (Moore et al
1988).
The laser technique
used to deliver this light is usually termed low level laser therapy (LLLT),
also referred to as low intensity laser therapy (LILT), low energy
photon therapy (LEPT) and phototherapy. Unlike the high intensity
medical lasers used to cut and coagulate tissues, LLLT involves the
use of medical lasers such as the Beurer SoftLaserTM that operate at
intensities too low to damage living tissues. Unlike most LLLT devices
that are relatively large and designed for clinical use, the Beurer
SoftLaserTM is a small, hand held, device designed for home use.
LIGHT
Light consists of those
wavelengths of the electromagnetic spectrum that are visible to the
human eye. This part of the spectrum extends from violet (the shortest
visible wavelength) to red (the longest visible wavelength). Infrared
(IR) is just beyond the visible range. The perceived colour depends on
the wavelength. White light is a mixture of all the visible
wavelengths. For photons to reach the skin, all that is required is
that it be either exposed to air or, if injured, to be covered by a
transparent dressing. Exposure to red light and/or infrared radiation
can stimulate the healing of both chronic injuries of the skin (Mester
et al 1985) and acute injuries (Dyson & Young 1986).
LASER
This is an acronym for
Light Amplification by the Stimulated Emission of Radiation. The
stimulated emission of radiation occurs when a photon interacts with
an energized atom. When an atom is energized, for example by
electricity, one of its electrons is excited, i.e. raised to a higher
energy orbit than its orbit when in the resting state. If the energy
of the incident photon is equal to the energy difference between the
electrons excited and resting states, then stimulated emission of a
photon occurs and the excited electron returns to its resting state.
This photon has the same properties as the incident photon, which it
also emitted. This process is repeated in the adjacent energized
atoms, producing a laser beam. Unlike light from non-laser sources,
this light is:
Monochromatic, i.e. of a single wavelength
Collimated, i.e. its light rays are non-divergent
Coherent, i.e. in phase, the troughs and peaks of the waves
coinciding in time and space.
With regard to the
biomedical effects of LLLT, monochromaticity is its most important
characteristic. To produce an effect, the light must be absorbed, and
absorption is wavelength-specific. Different substances absorb light
of different wavelengths. Mitochondria, present in all mammalian cells
except erythrocytes, contain cytochromes that absorb red light.
LLLT EQUIPMENT
This has three
essential components:
Lasing medium, which is capable of being energized sufficiently
for lasing to occur
Resonating cavity containing the lasing medium.
Power source that transmits energy into the lasing medium.
The type of lasing medium used determines the wavelength, and
therefore the colour, of the laser beam. For example, a HeNe laser, in
which the lasing medium is a mixture of helium and neon gases,
produces red light with a wavelength of 632.8 nm. Gallium, aluminium
and arsenide, the lasing medium of GaAlAs semiconductor diodes, also
produces monochromatic radiation, but the wavelength of this depends
on the ratio of these three materials and is in the red-infrared range
of the electromagnetic spectrum, typically 630-950 nm.
The resonating cavity containing the lasing medium has two parallel
surfaces, one being totally reflecting, the other being partially
reflecting. Photons emitted from the lasing medium are reflected
between these surfaces, some of them leaving through the partially
reflecting surface as the laser beam. The cavity of a HeNe laser is
many cms long, whereas that of a GaAlAs semiconductor diode is tiny,
the diode being the lasing medium and its polished ends the reflecting
surfaces. Modern low intensity laser therapy devices are generally of
the GaAlAs type. Their treatment heads may contain either one or
several diodes. Those with one diode resemble laser pointers and are
designed to treat acupuncture and trigger points; they can also be
used to treat points in and around skin injuries. Those with many
diodes are generally called cluster probes and allow large areas to be
treated rapidly. The diodes may be housed in a rigid head or in a
flexible material. The latter can be applied around curved surfaces
such as the shoulder. Each diode emits either red or IR radiation. Red
light is absorbed by all cells, whereas different wavelengths in the
infrared range appear to target specific cell types.
The power source for a LILT device may be either a battery or mains
electricity. Many LILT devices are portable. The main function of the
power source is to energize the lasing medium.
The Beurer SoftLaserTM
This hand-held LLLT
device is a low level Class 3A laser manufactured in Germany by Beurer
GmbH. It has a single probe containing a 5 mW GaAlAs diode producing
red light of 635-670 nm wavelength. It is powered by 2 AAA batteries.
Application of
SoftLaserTM to skin
The probe is placed in
contact with clean skin at right angles to the skins surface and
moved slowly over the region to be treated for a few minutes,
typically 3-6 minutes for a region of about 1 cm diameter. A
convenient way to use it is twice daily, shortly after cleansing the
skin in the morning and evening, and before the application of a
moisturizing cream and/or cosmetics.
LLLT EFFECTS ON
DAMAGED SKIN
Effects of the Beurer
SoftLaserTM on skin
The Beurer SoftLaserTM has been found by its users to:
Reduce wrinkles
Make scars less visible
Tighten large pores
Elevate pock marks
Improve skin tone
Give a temporary radiance to the skin
Soften chapped lips.
Treatment of damaged
skin with red light accelerates the resolution of inflammation,
leading to faster repair (Dyson 2004). The stimulated secretion of
collagen by fibroblasts at the site of a wrinkle or of a pock mark
will increase the thickness of the dermis locally, helping to fill in
the tissue deficit. The gradual removal of excessive scar tissue may
be due to the activation of fibroblasts, fibrocytes and other cells in
and around the scar.
As with any other technique, tissue repair can only be stimulated by
LLLT if it is absent or delayed. In these circumstances,
epithelialisation and granulation tissue production can be stimulated
by LLLT as can wound contraction (Dyson & Young 1986) This reduces
the area in which scar tissue is produced resulting in less obvious
scarring.
HOW LLLT PRODUCES ITS
EFFECTS
For LLLT to be
effective, the tissue targeted must absorb photons. Absorption is
wavelength dependent. Red light is absorbed by cytochromes in the
mitochondria; all human cells, other than mature red blood cells
(erythrocytes) contain mitochondria. Provided that appropriate
wavelengths and energy densities are used, cell activity can be
stimulated if it is suboptimal. Cells in which this has been
investigated include mammalian keratinocytes, lymphocytes,
macrophages, mast cells, fibroblasts and endothelial cells, all cells
of significance in tissue repair. Much of the research on this has
been reviewed by Baxter (1994) and by Tuner and Hode (2002). Cells
affected by LLLT show a temporary increase in permeability of their
cell membranes to calcium ions (Young et al 1990). This may be an
important component of the mechanism by which LLLT modulates cell
activity; other electrotherapeutic modalities, such as ultrasound, may
act in a similar fashion (Dyson 2004).
The triggering of cell activity by reversible changes in membrane
permeability when photons are absorbed could be responsible for the
stimulation of tissue repair (Young & Dyson 1993). Increase in
calcium uptake by macrophages exposed to red light and IR in vitro has
been shown to be wavelength and energy density dependent. Of the
wavelengths tested, 660, 820 and 870 nm were effective; 880 nm was
ineffective. These same wavelengths also affected growth factor
production by the macrophages, 660, 820 and 870 nm being stimulatory,
whereas 880 nm was not. Energy densities of 4 and 8 J/cm2 were found
to be effective; 2 and 19 J/cm2 were not (Young et al 1990). Red light
of 660 nm wavelength is absorbed by the cytochromes of mitochondria,
where it stimulates ATP production and increases cytoplasmic H+
concentration, which can affect cell membrane permeability (Karu
1988). IR radiation of 820 and 870 nm may be absorbed by components of
the cell membrane. Some of these components vary in different cell
types, which may be why the IR wavelengths absorbed by cells differ
according to the cell type. For example, 870 nm affects macrophages
(Young et al 1990) but not mast cells (El Sayed & Dyson 1990). It
may be possible to selectively stimulate macrophages but not mast
cells in vivo by exposure to an 870 nm probe.
Following a reversible change in membrane permeability to calcium
ions, the cells respond by doing what they are programmed to do. In
the case of macrophages, this is to produce growth factors and to
phagocytose debris, whereas fibroblasts manufacture collagen and other
extracellular components of the dermis.
The molecular mechanisms by which LLLT affects cell activity begin
with photoreception, when the photons are absorbed. This is followed
by signal transduction, amplification and a photoresponse, e.g. cell
proliferation, protein synthesis and growth factor production, all of
which may assist in tissue repair. Membrane structure differs
according to the cell type, which, if IR is absorbed by parts of the
membrane, may explain why different cell types absorb different
wavelengths of IR. Theoretically, it should be possible by the
judicious selection of IR wavelengths to affect some cell types while
leaving others unaffected. In contrast red light, since it is absorbed
by the mitochondrial cytochromes present in all mammalian cells other
than erythrocytes, and also by the hemoglobin contained in
erythrocytes, affects all mammalian cells.
Cellular effects
relevant to skin repair
The cellular effects of LLLT relevant to skin repair include the
stimulation of
adenosine triphosphate (ATP) production
growth factor release by macrophages
keratinocyte proliferation
collagen synthesis
angiogenesis.
All of the above are
required for skin to renew itself and repair the damage done to it by,
for example, environmental factors such as excessive exposure to the
elements, damage that accumulates with age.
Temporary
vasodilatation following the exposure to red light improves the
transport of essential nutrients and oxygen to the skin and the
removal of toxic waste materials from it. It also gives sallow skin a
radiant glow.
PAIN RELIEF BY LLLT
Although many of the
reports of pain relief following exposure to LLLT are anecdotal, there
have been a number of reports based on trials aimed at assessing LLLT
as an antinociceptive or analgesic modality, one of the earliest being
that of Walker 1983 who implicated alteration in serotonin metabolism
as one mechanism of LLLT-mediated analgesia.
Rheumatoid pain
Walker et al (1987) reported a highly significant reduction
(p<0.001) in the levels of pain and analgesic medication intake
reported by rheumatic patients either treated with low intensity red
laser or sham-irradiated, pain relief being greater in those given
laser treatment. Palmgren et al (1989) found that treatment of the
small joints of the hand in rheumatic patients with low intensity
infrared laser was followed by reduced pain and swelling, reduced
early morning stiffness and increased grip strength and range of
movement. In contrast Basford et al (1987) found that red laser
irradiation of the osteoarthritic thumbs of patients was not followed
by significant reduction in pain; however, the power and energy levels
used (0.9 mW and 0.081J) are well below those recommended for clinical
application (Baxter 1994) and may have been sub threshold.
Chronic neurogenic pain
Moore et al (1988a) have investigated the effect of red laser in the
treatment of patients with chronic neurogenic pain including that of
post-herpetic neuralgia. It was found that there was a significant
reduction in reported pain following treatment in comparison to that
in sham-irradiated patients. Similar effects have been reported by
Hong et al (1990) using the same equipment.
Mechanisms
It has been suggested by Obata et al (1990) that laser-mediated relief
of rheumatic pain may be linked to autonomic changes that produce
vasodilatation and slight increases in local temperature. It is also
possible that laser treatment affects the synthesis, release and
metabolism of a range of neurochemicals involved in nerve transmission
and pain relief (Walker 1983). Relief following the stimulation of
acupuncture points with LILT has been ascribed to the production of
endogenous opiate-like peptides and serotonin by Zhong et al (1989).
CONCLUSIONS
Scarring associated
with acne and skin deterioration due to ageing and sun damage can be
alleviated by LLLT. These skin conditions involve tissue injury, the
repair of which is improved by exposure to LLLT in the form of red
light. LLLT can reduce the duration of inflammation, improving tissue
repair where this is delayed or defective. It can also reduce both
acute and chronic pain. By assisting in the resolution of
inflammation, the proliferative phase of tissue repair begins earlier
and the reparative process is completed earlier. Cell activity is
jump-started by changes in membrane permeability. This occurs when the
cells absorb red and/or infrared radiation. The cells are also
energized when red light is absorbed by their mitochondria,
stimulating the synthesis of ATP and thus providing readily available
energy for cell activity. The improvement in the skin produced by LLLT
has been described as skin rejuvenation (Lee 2002). The Beurer
SoftLaserTM takes LLLT from the clinic into the home where it can be
used regularly for skin care.
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