What is red light therapy?

Red light therapy involves the use of visible light emitted from low-energy lasers with the goal of stimulating cellular processes. Red light is just one type of visible light on the electromagnetic spectrum (Figure 1). In addition to visible light, the electromagnetic spectrum includes radio waves, microwaves, infrared (IR), ultraviolet (UV), X-ray, and gamma rays. The implementation of light sources as a form of therapy is sometimes called photobiomodulation, and it aims to promote healing and regeneration, and/or to have a restorative function on target cells and tissues.

Red light, which has a wavelength between 620 to 750 nanometers (nm), contains energy that may become absorbed by target cells. Infrared light (750 to 1000 nm) is also sometimes used in red light therapy, despite being in the infrared range. In comparison to other visible wavelengths, red light is better able to penetrate deeper tissues due to a longer wavelength.ⁱ Light with longer wavelengths has lower energy compared to light with shorter wavelengths.

Red light therapy is often called low-level light therapy (LLLT), low-level laser irradiation, or laser acupuncture. It uses a type of light emitting diode (LED) light, which emits a relatively low level of energy in comparison to non-visible light or UV light.ⁱⁱ It is believed that exposure to red light is not associated with DNA damage, unlike UV light, which is known to increase the occurrence of skin cancer.ⁱⁱⁱ

There are a variety of proposed mechanisms as to how red light therapy works, but the exact mechanism remains unclear.^iv Exposure of human cells to certain light intensities has been shown to increase cellular processes, including cell proliferation (increase in cell number) and metabolism.^v,vi It has been proposed that the energy emitted by red light triggers these beneficial cellular responses when it is absorbed by mitochondria,^vii which are present in varying quantities in almost all cells. Mitochondria are cellular structures that produce energy in the form of adenosine triphosphate (ATP), which is used by the cell.^viii,ix

Red and near-infrared light have been used clinically as a noninvasive therapy for many years in fields other than fertility, such as dermatology, dentistry, and neurology. For example, it has been used to promote wound healing and to treat chronic joint pain.^x,xi It is believed that the benefits connected to red light therapy are based on improvements in blood flow and angiogenesis (creation of new blood vessels)^{xii, xiii} due to changes in a chemical compound called nitric oxide (NO), which is discussed below.^xiv

Can red light therapy improve fertility outcomes?

Red light therapy has been shown to have certain clinical benefits in other fields. However, research into red light therapy for fertility is still needed to support its clinical application.

Enhanced mitochondrial energy production

Photobiomodulation via red light therapy is believed to enhance mitochondrial energy production, particularly in stressed cells.^xv This effect is relevant to eggs and sperm because they both have a high quantity of mitochondria, which support their functional needs.

For example, the oocyte contains an extremely large number of mitochondria (100,000 to 100,000,000) compared to other types of cells (1,000 to 2,500),^xvi,xvii which is necessary due to the large energy demands of oogenesis and, later, embryonic development.^xviii,xix The sperm cell midpiece contains approximately 50 to 75 mitochondria, which is a high density for the small cellular area it occupies.^xx

Mitochondria from sperm do not become incorporated into the resulting embryo, although they are critical for sperm fertilizing capabilities. Embryonic mitochondria are derived from the oocyte and play a large role in energy production during early embryonic development.^xxi,xxii

Overall, proper oocyte and sperm cell mitochondrial function is imperative for fertility. Given the proposed advantages of red light therapy on the mitochondrial function in other cell types,^xxiii,xxiv there is the potential for improvement in fertility with the use of red light therapy.

Increased blood flow

In addition, red light therapy has also been shown to increase blood flow to treated tissues, which is believed to be mediated by an increase in nitric oxide (NO) formation.^xxv,xxvi NO, an effective antioxidant, acts to maintain healthy physiological levels of reactive oxygen species (ROS).

The body requires a certain level of ROS for proper cellular function; however, increased ROS levels cause a state of oxidative stress. Aging is associated with an increase in ROS accompanied by a decrease in antioxidants, which counteract negative ROS effects. Oxidative stress has well-documented detrimental impacts on both male and female fertility.^xxvii,xxviii Hence, in theory, red light therapy may address age-related fertility concerns by improving blood flow and reducing oxidative stress.

Red light therapy for male infertility: Research evidence

Sperm cells rely heavily on mitochondrial adenosine triphosphate (ATP) production for optimal sperm motility and physiological reactions necessary for fertilization.^xxix Some research findings suggest there may be beneficial effects of LED red light on sperm cells.^{xxx, xxxi, xxxii} The potential benefits may include increased cell survival and motility.

One of the first studies to investigate laser light exposure, conducted in the early 1980s, suggested that human ejaculate exposure to red laser light could stimulate motility in live sperm cells that were previously non-motile; however, no differences in sperm velocity were noted and the effects on reproductive outcomes (i.e., clinical pregnancy or live birth rates) were not investigated in the study.^xxxiii

A different small study found that red light exposure of frozen-thawed human sperm samples resulted in a significantly increased velocity compared to non-treated sperm.^xxxiv While the study observed no significant level of DNA damage induced by red light therapy, there was again no impact of red light therapy on reproductive outcomes.^xxxv

In 2014, researchers from Iran published findings examining the effects of red light therapy on human sperm motility using fresh semen specimens from patients with low sperm motility (called asthenospermia).^xxxvi The findings showed that sperm cells exposed to a low-level laser had increased progressive motility.^xxxvii

These three studies examining the effects of low-light therapy were performed on sperm cells collected from human ejaculate. However, the potential effects of direct exposure of the testes to red light in humans are not well-documented. Data collected from animal studies suggest photobiomodulation therapy impacts sperm quality when applied directly to the testes. Mice with heat-induced azoospermia, or lack of sperm, due to elevated testicular temperatures, underwent testicular IR laser exposure over the course of 21 days.^xxxviii Researchers found the mice receiving testicular laser treatment experienced a restoration of sperm cell production and overall healthier testicular tissue in comparison to the non-laser-exposed mice.^xxxix

One very small clinical study in Indonesia examined the effect of direct testicular irradiation in humans. The 20 study participants had their testicles irradiated for four minutes two times per week for a total of 10 sessions.^xl This laser treatment in males with azoospermia (absence of sperm in the ejaculate) did not lead to an improvement in sperm count. However, males with oligospermia (low sperm count) had an average 2.7-fold and 3.6-fold increase in sperm counts.^xli No adverse effects were reported by any of the 20 individuals included in the study.^xlii That said, there is a lack of good quality and validated published evidence related to using red light therapy directly on the testes, and further studies are needed.^xliii

Overall, there is little published evidence supporting the use of red light therapy for male fertility in humans. Furthermore, in the published studies showing potential improvement to sperm, the impact on reproductive outcomes, such as live birth rates, has not been studied.

Red light therapy for female infertility: Research evidence

It is well documented that fertility decreases with age in females, especially as they approach their mid-30s.^xliv,xlv One major factor driving this decline in female fertility with age is decreased oocyte quality.^xlvi The occurrence of aneuploidy (having too few or too many copies of a chromosome), becomes more common as females get older, likely due to the impact of age on chromosomes.

In addition, aging oocytes contain aged mitochondria, which may not be as efficient at energy production.^{xlvii,xlviii,xlix,l} Therefore, as red light therapy is believed to improve cellular mitochondrial function, there is the potential for red light therapy to also improve mitochondrial metabolism in aging oocytes. However, more research is needed to verify this benefit experimentally and clinically.

There are very few research studies that have thoroughly characterized the effect of red light therapy on female fertility. In 2010, a Japanese research group reported a clinical study where the effect of an IR laser (830 nm) was examined in female patients seeking fertility treatment.^li Although they observed that the females who became pregnant had received more IR therapy sessions than individuals that did not become pregnant (3.1 vs. 2.6 sessions),^lii there are various limitations to the study that prevent the results from being generalizable. For example, most of the patients were over 40 years old, with over half being 43 years or older in the non-pregnant group, and the pregnancy rate was very low (16.5 percent, 97/491).^liii Additionally, details of the specific type(s) of infertility treatment the patients received were not described. The study is included here to demonstrate the paucity of quality research in this area. Because of the study limitations, conclusions on any fertility impact cannot be made from these results.

Another study, from Iran, assessed the ability of direct red light exposure to help improve the maturation of immature oocytes retrieved from 36 females with polycystic ovary syndrome (PCOS) following ovarian stimulation for IVF.^liv The oocytes exposed to red light (640 nm) had a significantly higher rate of in vitro maturation (IVM, 111/155 reached MII mature stage) compared to the non-exposed control oocytes (78/159 reached MII stage).^lv This treatment was also accompanied by a decline in reactive oxygen species (ROS) compared to controls. The impact on fertilization rates or IVF outcomes were not investigated in the study.^lvi

Animal models have also been used to study the effects of photobiomodulation on female fertility. Using a rat model of PCOS, treatment with red light therapy was found to decrease the number of ovarian cysts while increasing ovulation and follicle number, compared to a PCOS control group.^lvii The findings have not yet been validated in humans.

Another frequent cause of female infertility, poor endometrial receptivity, is a result of endometrial conditions that affect embryo implantation. One factor that may contribute to poor implantation is inadequate endometrial thickness.^lviii As red light laser therapy is known to enhance cell proliferation (cell division), it is being examined as a therapy method to increase endometrial thickness, though it is still in early experimental stages. Following the exposure of endometrial cell samples to a red laser of 635 nm in vitro (in a lab), researchers found the red light–exposed cells had significantly increased in cell number and surface area in comparison to control cells.^lix In addition, the red light therapy treatment increased the expression of genes known to be important to endometrial receptivity. It was also noted that multiple exposure periods further improved cell proliferation. Overall, this study suggests benefits for endometrial cells following direct exposure to red light therapy. However, it cannot yet be generalized in vivo (in living individuals) until more research is completed; the effects of red light therapy on endometrial function and fertility when applied directly on the pelvic region have not been thoroughly investigated.

There are currently no randomized control trials examining the use of red light therapy directly on the body for the improvement of fertility in either males or females. Randomized controlled trials are the gold standard in research when determining the effectiveness of potential treatment. Analysis of the current research suggests that red light therapy may potentially enhance the quality of both oocytes and sperm cells and increase endometrial cell receptivity in a laboratory setting, but there remains a lack of research supporting its clinical effectiveness.

Is red light therapy safe? Side effects of red light therapy

Red light therapy is an emerging technology in the field of fertility, and additional research is required to fully examine the safety, effectiveness, and both short-term and long-term effects.

Studies have investigated the safety of red light therapy for the treatment of other medical issues, such as musculoskeletal and dermatological conditions.^lx,^lxi Visible light therapies, such as red light therapy, do not use harmful, cancer-causing light rays such as UV. Further, there is no clinical trial data linking red light therapy with any significant negative side effects.^lxii However, it is worth noting that this has not been fully investigated directly in female pelvic structures or male genitalia.

While many devices are available on the market for at-home use, buyers should be aware of red light therapy devices marketed as “FDA approved,” as the FDA does not approve these devices.

Consumers, especially males, should be cautious of red light therapy devices that produce heat. It is critical for sperm production that testicular temperature remains approximately two to three degrees Celsius below body temperature; therefore, heat-emitting red light devices may have a negative impact on spermatogenesis and overall male fertility.^lxiii

It has been suggested that one potential unwanted side effect of red light therapy is DNA damage due to reactive oxygen species (ROS) that are generated in the process. For example, 630 nm laser light stimulation has been shown to increase production of ROS such as hydrogen peroxide (H₂O₂) in mouse sperm.^lxiv At high levels, reactive oxygen species can damage the DNA inside a cell and thus researchers have suggested that this potential side effect should be investigated further. One 2017 study showed that oxidative damage was not increased in sperm exposed to 633 nm red laser light in order to improve sperm motility. The study analyzed oxidative damage in the sperm DNA and found no evidence that irradiation caused DNA damage.^lxv

Similarly, researchers reported in 2023 that red light treatment of human PCOS oocytes undergoing in vitro maturation experienced a decrease in ROS levels, accompanied by a decrease in cell degradation–related gene expression.^lxvi

A study in Egypt using cultured endometrial cells examined potential negative effects of sustained laser exposure.^lxvii Findings showed that the higher laser dosage and increased laser exposure time (20 minutes vs. 10 minutes) resulted in thermal damage to endometrial cells. While this study was conducted in a lab using cultured endometrial cells, findings from this experiment further emphasize the importance of exercising caution around laser strength and exposure time when considering red light therapy.^lxviii

Given the variability of study results to date, individuals seeking red light therapy for fertility benefits should remain cautious, as various companies market red light therapy and associated devices without strong peer-reviewed evidence to back them up.

Timing and logistics

Some fertility providers may offer red light therapy add-ons for fertility treatment, but it is not common practice and lacks evidence of effectiveness. Red light therapy may also be offered by medical spas and at acupuncture clinics. Medical LED light therapy devices are also available for purchase for at-home use, though there is very little evidence for their effectiveness.

A specific type of red light therapy, called laser acupuncture, can be offered the day of embryo transfer.^lxix This therapy includes the use of a small pen-like device that emits a low-level red light laser. Treatment can be focused on points often targeted with regular acupuncture such as the ears, abdomen, arms, legs, and top of the head for approximately half a minute per area.^{lxx, lxxi} This treatment is painless and can be offered before the transfer, after the transfer, or both. The goal of laser acupuncture is to increase blood flow to the uterus and increase implantation success.^lxxii

There are larger red light (and near-red light) emitting devices that are available for focusing on the abdominal/pelvic area to focus treatment on the uterus and/or ovaries. Therapy sessions are usually recommended for a duration of 20 minutes.^lxxiii,lxxiv Because red light therapy is believed to impact cellular activity by increasing mitochondrial production of ATP, there is theoretical potential for red light therapy to improve egg quality which would increase fertility. Additionally, females may also potentially benefit from red light therapy by promoting blood flow to support embryo implantation.^{lxxv, lxxvi}

Red light therapy for male fertility may be offered using similar devices at acupuncture clinics. This therapy directs red light to the cells located in the testicles that stimulate sperm production, known as Sertoli cells. For males seeking sperm-related benefits, red light therapy sessions could theoretically be beneficial up to three months in advance for couples seeking assisted reproductive technologies including IUI or IVF. While males produce sperm every day, the period it takes to produce mature, motile sperm from immature spermatogonia is approximately three months.^lxxvii

Conclusion

Red light therapy may hold promise for enhancing male and female fertility by potentially improving mitochondrial energy production, blood flow, and reducing oxidative stress. However, the available peer-reviewed research in this area is minimal. While preliminary research is encouraging, further clinical studies are necessary to confirm its theoretical effectiveness. Although there are no studies indicating negative side effects of red light therapy, additional studies are required to address any potential risks and to ensure general safety.

Patients reading about red light therapy on blogs, social media, or other non-scientific sources should be wary of claims that red light therapy for fertility is supported by clinical research. Given the lack of evidence, and lack of support from medical societies, individuals considering red light therapy for fertility should consult with medical professionals before using red light therapy during their fertility journey.