[6][7] Several such devices are cleared by the United States Food and Drug Administration (FDA), and research shows potential for treating a range of medical problems including rheumatoid arthritis[8] and oral mucositis.

In LLLT that chemical substance is represented by the respiratory enzyme cytochrome c oxidase which is involved in the electron transport chain in mitochondria,[12][13] which is the generally accepted theory.

Various LLLT devices have been promoted for use in treatment of several musculoskeletal conditions including carpal tunnel syndrome (CTS), fibromyalgia, osteoarthritis, and rheumatoid arthritis.

LLLT appears to be effective for preventing oral mucositis in recipients of a stem cell transplant with chemotherapy.

Concerns have been raised in the literature about brain stimulation techniques that rely upon low-level (low-power) lasers and light-emitting diodes (LEDs).

Brennen McKenzie, president of the Evidence-Based Veterinary Medicine Association, has stated that "research into cold laser in dogs and cats is sparse and generally low quality.

[35] Scientific evidence for some of his treatments is lacking, and later eradication of smallpox and development of antibiotics for tuberculosis rendered light therapy obsolete for these diseases.

[12] In 1974, he founded the Laser Research Center at the Semmelweis Medical University in Budapest, and continued working there for the remainder of his life.

[37] Mester originally called this approach "laser biostimulation'", but it soon became known as “low-level laser therapy" and with the adaptation of light emitting diodes by those studying this approach, it became known as "low-level light therapy", and to resolve confusion around the exact meaning of "low level", the term "photobiomodulation" arose.

[47] Cigna lists LLLT as "experimental, investigational, or unproven for any indication" and provides literature review summaries for a number of conditions.

[17] In 2013, however, a systematic review and meta-analysis of LLLT for neck pain indicated that the benefit was not of significant importance and that the evidence had a high risk of bias.

[55] There are tentative data that LLLT is useful in the short-term treatment of pain caused by rheumatoid arthritis,[8] and possibly chronic joint disorders.

These outcomes included pain, functional capacity, adverse events, inflammation, disease activity, range of motion, stiffness in the morning, muscle strength, and quality of life.

[56] The findings indicate that the differences between utilizing a sham and an infrared laser may be negligible or nonexistent in terms of pain, stiffness in the morning, grip strength, functional ability, inflammation, range of motion, disease activity, and side events.

We also discovered that the data about the effects of laser acupuncture against reflexology in terms of functional ability, quality of life, and inflammation is quite hazy, and about the effects of red laser versus sham in terms of pain, morning stiffness, and side events.

The types of devices (hat, comb, helmet) and duration did not alter the effectiveness,[72] with more emphasis to be placed on lasers compared to LEDs.

[81] However, as of 2012[update] and due to inconsistent results and the low quality of extant research, reviews in the scientific literature have not supported its widespread application.