The Low Level Laser Therapy -
LLLT Internet Guide

FAQ - frequently asked
questions about laser therapy


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Q: What is laser therapy
Q: What is the correct name (LLLT, LPT; LPLT, low power laser, biostimulation)?

Q: Is laser therapy scientifically well documented?
Q: Where do I find such documentation?
Q: But I have heard that there are dozens of studies failing to find any effect of LLLT?
Q: Which lasers can be used in medicine?
Q: Can therapeutic lasers damage the eye?
Q: How do I know which laser I should buy?
Q: How come some LLLT equipment has power in watts and some only in milliwatts?
Q: Which frequency (pulsing) should be used for the various therapies?
Q: Which type of laser is best suited to which job?
Q: Can carbon dioxide lasers be used for LLLT?
Q: How deep into the tissue can a laser penetrate?
Q: Can LLLT cause cancer?
Q: What happens if I use a too high dose?
Q: Are there any contraindication?
Q: Does LLLT cause a heating of the tissue?
Q: Does it have to be a laser? Why not use monochromatic non coherent light?
Q: Does the coherence of the laser light disappear when entering the tissue?
Q: Do therapeutic lasers produce so-called soliton waves?

Q: What is laser therapy?

A: Laser therapy or Laser Phototherapy is a method where light from a laser is applied to tissue (or cells in culture) in order to influence cell or tissue functions with such low light intensity that heating is negligable. The effects achieved are hence not due to heating but to photochemical or photobiologic reactions like the effect of light in plants. The lasers used are normally called therapeutic lasers or medical lasers.

This is in contrast to the use of lasers in surgery and for esthetic purpose where strong lasers are used and where the biologic effects (cutting, evaporating, coagulating) are based on heat development from the absorption of strong light, i.e. burning glass effect.

Q: What is the correct name: LLLT, LPLT, therapeutic laser, soft laser, MID laser or biostimulation?

Regarding the therapy, we have chosen to use the term LLLT (Low Level Laser Therapy). This is the dominant term in use today, but there is still a lack of consensus. In the literature LPLT (Low Power Laser Therapy) is also frequently used.
Regarding the laser instrument, we have chosen to use the term "therapeutic laser" rather than "low level laser" or "low power laser", since high-level lasers are also used for laser therapy.
The term "soft laser" was originally used to differentiate therapeutic lasers from "hard lasers", i.e. surgical lasers. Several different designations then emerged, such as "MID laser" and "medical laser".
"Biostimulating laser" is another term, with the disadvantage that one can also give inhibiting doses. The term "bioregulating laser" has thus been proposed. An unsuitable name is "low-energy laser". The energy transferred to tissue is the product of laser output power and treatment time, which is why a "low-energy laser", over a long period of time, can actually emit a large amount of energy. Other suggested names are "low-reactive-level laser", "low-intensity-level laser", "photobiostimulation laser" and "photobiomodulation laser".
"LPT - Laser Photo Therapy" is a recently suggested term, and winning acceptance.
Thus, it is obvious that the question of nomenclature is far from solved.
This is because there is a lack of full agreement internationally, and the names proposed thus far have been rather unwieldy. Feel free to forget them, but remember LLLT until agreement is reached on something else.

Q: Is laser therapy scientifically well documented?

A: Basicly yes. There are more than 130 double-blind positive studies confirming the clinical effect of LLLT. More than 3000 research reports are published. Looking at the limited LLLT dental literature alone (370 studies already in 1999), more than 90% of these studies do verify the clinical value of laser therapy. About 250 papers are annually published in peer reviewed scientific papers.

Q: Where do I find such documentation?

A: The book "Laser Therapy Handbook" is the best reference guide for literature documentation. Abstracts from scientific papers can be found on PubMed,

Q: But I have heard that there are dozens of studies failing to find any effect of LLLT?

A: That is true. But you cannot just take a any laser and irradiate for any length of time and using any technique. A closer look at the majority of the negative studies will reveal serious flaws. Look for link under Laser literature and read some examples. But LLLT will naturally not work on anything. Competent research certainly has failed to demonstrate effect in several indications. However, as with any treatment, it is a matter of dosage, diagnosis, treatment technique and individual reaction. Se link critic on critic.

Q: Which lasers can be used in medicine?

A: Examples of lasers which can be used in medicine, both for surgery and therapy:

Therapeutic lasers (where the mechanism is not based oh heat):

Laser Wavelength Use
GaAs 904 nm (super pulsed) Treatment of deep problems (back, shoulders, knees, head ache etc)
GaAlAs 780-808-890 nm (cont. or chopped) Also deep problem, often a complement ot the GaAs-laser
InGaAlP 630-700 nm Treatment of skin and mucose problems
HeNe 633 nm Alternative to InGaAlP (see above)

Thermal lasers (for surgery or esthetic use):

Laser Wavelength Use
Ruby 694 nm Hair removal (for Q-switch type: tattoo bleaching)
Nd:YAG 1064 nm Coagulation of tumors, eye surgery (cataracts)
Ho:YAG 2130 nm Crushing of kidney stones, surgery
Er:YAG 2940 nm Dental drill, laser peeling of wrinkles and scars
KTP/532 532 nm Coagulation of blood vessels, hemangioma.
Alexandrite 755 nm Hair removal (for Q-switch type: tattoo bleaching)
CO2  laser 10600 nm Surgery and laser peeling of wrinkles and scars
Argon 514 nm Eye surgery (treatment of retinopathy)

There are many other types, but those mentioned above are the most common.

Q: Can therapeutic lasers injure your eyes?

A: Yes and no! Read the following:

Any strong light source - laser or not - can injure an eye.There are strong lasers that can cut in plastic and even steel. They can injure eyes and tissue, but laser pointers and therapeutic laser can normally not. Read more below:

The following factors are of importance regarding the eye risk of different lasers:

The output power (strength) of the laser. It is fairly obvious that a powerful laser (many watts) is more hazardous to stare into than a weak laser.

The divergence of the light beam. A parallel light beam with a small diameter is by far the most dangerous type of beam. It can enter the pupil, in its entirety, and be focused by the eye's lens to a spot with a diameter of hundredths of a millimetre. The entire light output is concentrated on this small area. With a 10 mW beam, the power density can be up to 12,000 W/cm2

The exposure time. To burn the retina, a certain energy is needed. Energy is power multiplied by time, so exposure time is important.

The wavelength of the light. Within the visible wavelength range, we respond to strong light with a quick blinking reflex. This reduces the exposure time and thereby the light energy which enters the eye. Light sources which emit invisible radiation, whether an infrared laser or an infrared diode, always entail a higher risk than the equivalent source of visible light. Radiation at wavelengths over 1400 nm is absorbed by the eye's lens and is thus rendered safe, provided the power of the beam is not too high. Radiation at wavelengths over 3,000 nm is absorbed by the cornea and is less dangerous.

The distribution of the light source. In an eye, like in a camera, the image of the source is projected on the retina/film. In a laser, the source is very small, so it is depicted as a point (compare with a burning glass where you get a picture of the sun in the focus "point"). A widely spread light source is projected onto the retina in a correspondingly wider image, in which the light is spread over a larger area, i.e. with a lower power density as a consequence. For example: a clear light bulb is apprehended as a more concentrated light source than a so-called "pearl" light bulb. A laser system with several light sources placed separated from each other (often called multi probe) constitutes a smaller hazard to the eye than if the entire power output was from one laser source, because the light sources separate placement means that they are reproduced in different places on the retina.

In conclusion. Lasers in general are much less dangerous than people think. No person has become blind by a laser. A few people have got injuries. Normally they will not notice such an injury. Even in the worst cases (where the inury is extensive and in the midle of the fovea) the consequensies are much less than any injury caused by stones, knifes, dart arrows, fireworks, dry branches int the forrest etc. See further the presentation named: What lasers can make you blind?


Q: How do I know which laser I should buy?

A: The laser market is very complicated and full of pitfalls. How do you know which instruments are good? What is expensive? Will it be expensive in the long run to buy something cheap? It is easy to make hasty decisions when faced with a skilful salesman - who is likely to know much more about the field than the customer. Before you know it, you've signed on the dotted line. All lasers are given a laser class. This classification is only to indicate the possible eye risk and has nothing to do with the possible efficktiveness in treatment. There are four laser classes where class 4 is the strongest and class 1, 2 and 3A and 3B are less hazardous to eyes. Lasers in CD players and for reading bar codes are usually class 1 lasers while surgicla and industial lasers usually are class 4 lasers.

Here are a number of questions which you should ask both the salesman and yourself. You would be well advised to read these carefully in case you regret not doing so later on!

1 "Laser instruments" have been sold which do not even contain a laser, but LEDs or even ordinary light bulbs. These instruments have been sold for between US $3,000 - $10,000. How can you acquire proof that the instrument really does contain a laser?

2 In a number of products, laser diodes have been combined with LEDs. This is often kept secret and the salesman has only talked about a laser. Are all light sources in the apparatus (except guide lights and warning lights) really lasers?

3 Is a strong laser better than a week? No, not necessarily. There is an optimal dose for what ever treatment - let's say that you want to administer 10 joules to a certain area. If the laser output is 1 watt, it takes 10 seconds to give 10 joules. With a 100 mW laser it takes 100 seconds to produce 10 joules. Further, it has become clear that also treatment time should not be too short or too long. As high power has become a more and more common sales argument, it can be difficult to achieve both optimal dose and optimal treatment time. Naturally, also a too weak laser can make the treatment less successful.

4 For oral work and wound healing, InGaAlP and GaAlAs are the most common types, with GaAlAs as the most versatile one. For injuries to joints, vertebrae, the back, and muscles, that is, for the treatment of more deep-lying problems, the GaAs laser is the best documented. For veterinary work, a laser is needed which is designed so that the laser light can pass through the coat, and penetrate to the desired depth. For superficial tendon and muscle attachments, the required depth can be reached with the GaAlAs laser. Many companies have only one type of laser, such as a GaAlAs, and the salesman will naturally tell you that it is the best model for everything, and that it is irrelevant which type of laser is used. However, research tells quite a different story. GaAs further requires lower dosage than GaAlAs, so nominal power is not everything.

5 Size, colour, shape, appearance and price vary a great deal from manufacturer to manufacturer. Because a piece of equipment is large, it does not necessarily follow that its medical efficacy is high, or vice versa. The most important factor is the energy (dose) which enters the tissue. Make sure the laser you buy is designed so that all the light actually enters the tissue. Ask the salesman: how is the dose measured? What dose is too high, and what is too low?

6 Many companies which import lasers have deficient knowledge in terms of medicine, laser physics, and technology. In fact, there are many examples of companies which have gone bankrupt. If a piece of equipment is faulty, it may have to be sent to the country of manufacture for repair. How long would you be without your equipment in such a case, and what would it cost to repair? Can the importer document his expertise? Who can you speak to who has used the apparatus in question for a long period of time? Is there a well-known professional who uses this make? What does it cost to change a laser diode or laser tube, for example, after the guarantee has expired? Can you get written confirmation of this? Try to get a list of references who you can call and ask.

7 The difference between a colourful brochure and reality is often considerable. There are examples of brochures which describe output ten times that which the equipment actually provides. How can you find out the real performance of the equipment (e.g. its output)? Are there measurement results from an independent authority? Is it possible to borrow an apparatus in order to measure its performance? Is there a power meter on the apparatus which can measure what is emitted and show it in figures? It is not enough simply to have a light indicator.

8 Some dealers know that their products are sub-standard. This can often be seen by the fact that they are anxious to get the customer to sign a contract. If a product is good, the dealer will have no doubts about selling it on sale-or-return basis, with written confirmation of this. What happens if the medical effects are not as promised? Is it possible to get a written guarantee of sale-or-return?

9 In most countries, therapy lasers must be approved (e.g. CE or FDA approval). The approval certificate shows the laser type and the class to which the instrument belongs, e.g. laser class 3B. There is also a certificate number. A laser which is not approved may either not be a laser, or might be sold illegally.

10 Many companies organize courses and "training" events of markedly varying quality. A serious importer or manufacturer takes pains to ensure that his equipment is used in a qualified way, and makes sure that the customer receives some training in its use. What are the instructor's background and qualifications? Has he or she published anything? Is there a course description? What does the training material cost? Is a training course included in the cost of the equipment? Is the training material included? Is it possible to buy the training material only?

11 Development is going on at a fast pace. Suddenly, you have out-of-date laser equipment and a new and perhaps more efficient type of laser comes onto the market. What happens if your laser becomes outmoded? Do you have to buy a new laser, or can your equipment be updated with future components lasers?

12 Is it possible to get education or a qualified treatment manual? Is literature included in the price?

Q: How come some LLLT equipment has power in watts and some only in milliWatts?

A: A typical example is GaAs lasers. As a GaAs laser always works in a pulsed fashion, the laser light power varies between the peak pulse output power and zero. Then usually the laser's average power output is of importance, especially in terms of dose calculation. The peak pulse power value is of some relevance for the maximum penetration depth of the light. Some manufacturers specify only the peak pulse output in their technical specifications. "70 W peak pulse output" or even "70 000 mW power output" naturally sounds more impressive than 35 milliwatts average output!

Q: Which frequency (pulsing) should be used for the various therapies?
A: First we must differentiate between “chopping” and “superpulsing”. Some lasers, like the GaAs laser, are always pulsed. The pulses are very short but the peak power of the pulse is very high, several watts, but the pulse duration is typically only 100 to 200 nano seconds. Other lasers like the HeNe and the GaAlAs are normally continuous, but can be pulsed by mechanical or electrical devices. This means that the beam is turned off and on but the peak output power of each pulse is the same as if the light is continuous.
If a continuous laser is pulsed, the average output power will be lower. With most GaAs lasers the power decreases with lowered frequencies (unless there is a pulse train arrangement) and with “chopped” lasers we typically loose 50% (50% duty cycle).
There is some evidence from cell studies that the pulsing can makes a difference. But the evidence from clinical studies is almost absent. Since GaAs is always pulsed, we have to choose a frequency and then to use the anecdotal evidence there is about what frequency is good for what.
Q: Which type of laser is best suited to which job?

A: There are three main types of laser on the market: HeNe (now being gradually replaced by the InGaAlP laser), GaAs and GaAlAs. They can be installed in separate instruments or combined in the same instrument.

* The InGaAlP- or HeNe-laser has been used a great deal in dentistry in particular, as it was the first laser available. They are especially good for and have been used for wound healing for more than 40 years. One advantage is the documented beneficial effect on mucous membrane and skin (the types of problem it is best suited to), and the absence of risk of injury to the eyes. A Japanese researcher has even treated calves with keratoconjunctivitis with excellent results, that is, irradiation of the eye through the eye lid. Because HeNe light is visible, the eye's blink reflex protects it.

Normal HeNe output for dental use is 3-10 mW, although apparatus with up to 60 mW is available. An optimal dosage when using a HeNe laser for wound healing is 1-4 J/cm2 around the edge of the wound, and approximately 0.5 J/cm2 in the open wound. HeNe lasers are used to treat skin wounds, wounds to mucous membrane, herpes simplex, herpes zoster (shingles), gingivitis, pains in skin and mucous membrane, conjunctivitis, etc.

* The GaAs laser is excellent for the treatment of pain and inflammations (even deep-lying ones), and is less suited to the treatment of wounds and mucous membrane. Very low dosages should be administered to mucous membrane! Most GaAs equipment is intended for extraoral use, but there are special lasers adapted for oral use.

The GaAs laser is, like GaAlAs and InGaAlP lasers, a semiconductor laser. A purely practical advantage of this type of laser is that the laser diode is located in the hand-held probe. This means that there is no sensitive fibre-optic light conductor which runs from the laser apparatus to the probe, but just a normal, cheap, robust electric cable. Optimum treatment dosages with GaAs lasers are lower than with HeNe lasers.

The GaAs laser is most effective in the treatment of pain, inflammations and functional disorders in muscles, tendons and joints (e.g. epicondylitis, tendonitis and myofacial pain, gonarthrosis, etc.), and for deep-lying disorders in general. As mentioned above, GaAs is not thought to be as effective on wounds and other superficial problems as the HeNe laser (InGaAlP laser) and GaAlAs laser. GaAs can, nevertheless, be used successfully on wounds in combination with HeNe or InGaAlP, but the dosages should be very low - under 0.5 J/cm2.

* The GaAlAs laser can have a wavelength in the interval 750 to 980 nm and has become increasingly popular. Most common wavelength is 808 nm. As they are very easy to run electrically, small rechargeable lasers have been put on the market, often not much larger than an electrical toothbrush. (They can run on normal or rechargeable batteries.). GaAlAs lasers have appeared on the market with an output of over 500 mW.

200-300 mW laser diodes are now relatively cheap and the GaAlAs laser gives "a lot of milliwatts for the money". Recently, GaAlAs lasers have appeared on the market with an impressive output of over 500 mW. In Europe, GaAlAs laser with powers above 500 mW can only be used by doctors and dentists, being Class 4 lasers.

Many InGaAlP/GaAlAs lasers have well-designed, exchangeable, sterilizable intraoral fiber tips (light guides). For the infrared types especially, output power meters are essential because the light is invisible.

Q: Can carbon dioxide lasers be used for LLLT?

A: Yes. Therapeutic laser treatment with carbon dioxide lasers has become more and more popular. This does not require instruments expressly designed for that purpose. Practically any carbon dioxide laser can be used as long as the beam can be spread out over an appropriate area, and as long as the power can be regulated to avoid burning. This can always be achieved with an additional lens of germanium or zinc selenide, if it cannot be done with the standard accessories accompanying the apparatus.
It is interesting to note that the CO2 wavelength cannot penetrate tissue but for a fraction of a mm (unless focused to burn). Still, it does have biostimulative properties. So the effect most likely depends on transmittor substances from superficial blood vessels. Conventional LLLT wavelengths combine this effect with "direct hits" in the deeper lying affected tissue.

Q: How deep into the tissue can a laser penetrate?

A: The depth of penetration of laser light depends on the light's wavelength, on whether the laser is super-pulsed, and on the power output, but also on the technical design of the apparatus and the treatment technique used. A laser designed for the treatment of humans is rarely suitable for treating animals with fur. There are, in fact, lasers specially made for this purpose. The special design feature here is that the laser diode(s) obtrude from the treatment probe rather like the teeth on a comb. By delving between the animal's hair, the laser diode's glass surface comes in contact with the skin and all the light from the laser is "forced" into the tissue.

A factor of importance here is the compressive removal of blood in the target tissue. When you press lightly with a laser probe against skin, the blood flows to the sides, so that the tissue right in front of the probe (and some distance into the tissue) is fairly empty of blood. As the haemoglobin in the blood is responsible for most of the absorption, this mechanical removal of blood greatly increases the depth of penetration of the laser light.

It is of no importance whether the light from a laser probe, held in contact with skin is a parallel beam or not.

There is no exact limit with respect to the penetration of the light. The light gets weaker and weaker the further from the surface it penetrates. There is, however, a limit at which the light intensity is so low that no biological effect of the light can be registered. This limit, where the effect ceases, is called the greatest active depth. In addition to the factors mentioned above, this depth is also contingent on tissue type, pigmentation, and dirt on the skin. It is worth noting that laser light also penetrate bone (as well as it can penetrate muscle tissue). Fat tissue is more transparent than muscle tissue.

For example: a InGaAlP laser with a power output of 35 mW has a greatest active depth of about 10 mm depending on the type of tissue involved. A GaAlAs probe of some strength has a penetration of 35 mm and a GaAs laser has a greatest active depth of between 30 and 40 mm (sometimes down to 50 mm), depending on its peak pulse output (around a thousand times greater than its average power output). If you are working in direct contact with the skin, and press the probe against the skin, then the greatest active depth will be achieved.N.B. Clothes will reduce penetration between 80 and 100% depending on thickness and colour.

Q: Can LLLT cause cancer?

A: The answer is no. No mutational effects have been observed resulting from light with wavelengths in the red or infra-red range and of doses used within LLLT.

But what happens if I treat someone who has cancer and is unaware of it? Can the cancer's growth be stimulated? The effects of LLLT on cancer cells in vitro have been studied, and it was observed that they can be stimulated by laser light. However, with respect to a cancer in vivo, the situation is rather different. Experiments on rats have shown that small tumours treated with LLLT can recede and completely disappear, although laser treatment had no effect on tumours over a certain size. It is probably the local immune system which is stimulated more than the tumour.

The situation is the same for bacteria and virus in culture. These are stimulated by laser light in certain doses, while a bacterial or viral infection is cured much quicker after the treatment with LLLT

Q: What happens if I use a too high dose?

A: You may have a biosuppressive effect or just a non optimal effect. That means that, for instance, the healing of a wound will take longer time than normally. Very high doses on healthy tissues will not damage them.

Q: Are there any contraindications?

A: No, no medical contraindications. In most countries there are legal contraindications, i.e. you should not treat cancer or some other seious deseases. Pregnancy is not a contra indication if treatment is done with common sense. Pacemakers are electronical and are not influenced by light. The most valid contraindication is possible lack of adequate medical treatment.

Q: Does LLLT cause a heating of the tissue?

A: Principally yes - all light will cause some heating if absorbed by tissue. However stronger laser types. like GaAlAs lasers in the 300-500 mW range may cause a noticeable heat sensation, particularly in hairy areas, dark tattoo and on sensitive tissues such as lips. The amount of melanin in the skin is an important factor; dark skin will be more heated than fair skin. The biological effects have nothing to do with heat. Due to increased circulation there is usually an increase of 0.5-1 degrees Celcius locally.

Q: Does it have to be a laser? Why not use monochromatic non coherent light?

A: Monochromatic non coherent light, such as light from LED's can give good effect on superficial tissues such as wounds. In comparative studies, however, lasers have shown to be more effective than monochromatic non coherent light sources, especially in deep tissue.


Q: Does the coherence of the laser light disappear when the light is scattered in the tissue?

A: No. The length of coherence, though, is shortened. Through interference between laser rays in the tissue, very small "islands" of more intense light, called speckles occur. These speckles will be created as deep as the light reaches in the tissue and within a speckle volume, the light is partially polarized. It is easy to show that speckles are formed rather deep down in tissue and the existence of laser speckles prove that the light is coherent.


Q: Do therapeutic lasers produce so-called soliton waves?

A: No. Such claims are just sales tricks.


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