Optimizing Red Light Therapy for Dark Skin Types
Studies including people with darker skin types are often lacking in Photobiomodulation and LLLT literature.
The published dosing guidelines by the World Association for Laser Therapy (WALT) are noted to be for Caucasian skin types:
"Recommended doses are for white/caucasian skin types based on results from clinical trials or extrapolation of study results with similar pathology and ultrasonographic tissue measurements."
https://waltpbm.org/documentation-links/recommendations/
While many studies acknowledge the potential impact of skin color on Photobiomodulation dosing and effects, it has not been thoroughly investigated yet.
One review article attempted to investigate the effects of using PBM to treat diabetic foot ulcers based on skin color, but of the 15 studies they reviewed; only one reported the skin color demographics and adjusted the dose based on skin type.[1]
"Most studies conducted thus far on PBM do not mention the skin color nor race of patients, which should be considered due to varying photon absorbencies by melanin. Only one of the studies evaluated in this review took skin color into consideration and adjusted the dose accordingly. " [1]
It is recommended that studies record the skin color of the participants in order to make analysis of results based on skin type. Even if no adjustment to the parameters is made yet, this will be valuable data to use in the future to improve treatments.
"Complete reporting should also include the distance of the light device from the tissue surface, spot size (cm2), skin color, and use of the current terms" [2]
In this blog we review the PBM articles that discuss how skin color impacts red light therapy, and the recommended dosing adjustments that can be made to improve results based on skin phototype.
Melanin and Photobiomodulation
Melanin is a pigment in the skin that primarily protects from excess sunlight exposure. Inevitably, this has a significant impact on light therapies.
Having a darker skin type means there is a higher concentration of melanin in the skin. Lighter skin types means there is relatively less melanin in the skin.
With higher melanin concentrations, wavelengths of light will be more superficially absorbed by this pigment. This leads to a reduction of light penetration, less dosage reaching target tissue, and superficial heat effects.
"Skin color and skin thickness affect transmittance and reflectance of laser light and must be accounted for when selecting energy dose to ensure therapeutic effectiveness at the target tissue. " [3]
For optimal red light therapy - adjustments to the wavelengths, intensity, application modes, and/or dose may be required to produce better results depending on Skin PhotoType (SPT).
Summary:
There are two main theories for how to dose based on Skin PhotoType for Photobiomodulation (PBM).
1. As long as the device parameters and dosage are considered safe and non-thermal for all skin types, most studies make no adjustments based on Skin PhotoType for patients.
2. Adjustments for darker skin types may include:
- A preference for Near-Infrared (NIR) wavelengths (800nm+) to improve penetration and reduce superficial heating from Red wavelengths.
- Reduce the intensity by up to 50% to reduce heat effects from high intensity devices (or as-needed).
- Use pulsed modes or other cooling methods to reduce skin heating.
- Increase the dosage by up to 25-50% to ensure adequate energy reaches the deeper tissue. This means multiplying the typical dose by 1.25 or 1.50.
These adjustments may be more important for treating deeper tissue. Reducing the intensity by even 25% and increasing the dose by 25% also means the exposure time will be increased by around 1.6 times!
For skincare and superficial treatments, it is likely fine to use the same parameters for all skin types - again assuming it is mostly non-thermal intensity and a reasonable dosage.
Background: Skin PhotoType and Vitamin D from Sunlight
The Fitzpatrick scale from I to VI (one to six) is used to describe the general range of skin color in humans as determined by the melanin concentration in the skin.This is also shortened to Skin Phototype (SPT). [4]
A higher melanin concentration is important for UV protection from the sun.
A standard metric called the Mean Erythyma Dose (MED) is when the skin reddens from UltraViolet (UV) dosage (i.e. what we call Sunburn). The MED is 2-6 times larger for dark skin types compared to light skin types due to higher protection factor provided by the melanin. [5]
Which is overall a good thing in terms of protection from skin cancers, as is one of the functions of the Fitzpatrick PhotoType scale is to determine relative risk of skin cancer. With lighter skin types being 20-32 times more prevalent to skin cancers due to a lack of natural UV protection from melanin. [5]
However, some studies have found that people with darker skin types produce 1.3 to 6 times less Vitamin D than the same UV dose delivered to the lighter skin types.[6] These experiments confirm the reason why surveys find a correlation between people with darker skin types and Vitamin D deficiency. [7]
Another study mentions:
"Individuals with lighter skin can generate >50 nmol/L of 25(OH)D from 30 minutes of sun exposure daily, but darker skin requires upwards of two hours of exposure to reach the same amount produced "[7]
Requiring 4 times more sunlight exposure time than lighter skin types to produce the same amount of Vitamin D.
We introduce this background section to remind people how sunlight is essential to optimal health, and the parallel that longer exposure times may also be required for red light therapy for people with darker skin types.
Interestingly, it was noted in one study that the Fitzpatrick skin phototype scale was originally developed to help clinicians adjust the dose for UV-A treatment for psoriasis. The same concepts may apply to Red Light Therapy. [8]
Skincare / Dermatology Photobiomodulation for Dark Skin
Several studies have been conducted with Fitzpatrick Skin types ranging from II to VI with Red and Blue LED phototherapy to manage acne.[9][10][11]
A review article titled "Acne Vulgaris in Skin of Color: A Systematic Review of the Effectiveness and Tolerability of Current Treatments" concludes:
"Overall, LED appears to be tolerable and effective therapy for acne vulgaris in skin of color patients." [12]
One study used the Ominlux 633nm and 830nm clinical grade system for an improvement in melasma with 60 females Fitzpatrick IV-V. They used the same dosing protocol that is also used for skin rejuvenation trials for other skin phototypes. [13]
A study using the Omnilux for Men LED mask notes that people with darker skin types are more susceptible to postinflammatory hyperpigmentation, erthemya, and blistering particularly at higher intensities or doses. [14]
However, they reassure the reader that LED face masks have a large margin of safety for skincare even for darker skin types:
"The commercially available face mask doses used for treatment are far below this threshold associated with adverse events in skin of color patients. Larger randomized controlled trials (RCTs) with more racial and ethnic representation are needed to further evaluate safety, efficacy, and overall experience using PBM in darker skin types." [14]
As is often noted, there is a call to action that more studies are needed with better diversity in order to truly optimize the safety and effectiveness.[14]
So for superficial applications like skincare, it is likely fine to use the same dosing parameters for all skin types.
Dosing - No Adjustments Needed Based on Skin Phototype
The general sentiment for dosing is summarized by the following quote. The parameters of PBM do not need to be adjusted based on skin type as long as it is non-thermal for all skin types.
"As the PBMT device used in the study causes no harmful thermal effects,[23] volunteers of different skin colors will be recruited." [15]
However, a recent 2024 study using PBM for plantar fasciitis found that the patients with darker skin types had poorer outcomes than people with lighter skin types. Although some benefits were gotten using the same dose for all skin types, it likely could have improved with some adjustments.
"The study had a significant finding that higher Fitzpatrick category was predictive for poorer outcomes in the FAAM ADL and sports subscale, but had no significant impact on pain. Though these results should be interpreted cautiously due to the small number of participants in higher Fitzpatrick categories, it is important to remember when designing treatment protocols to consider using a longer wavelength option (e.g., 980 nm) for those individuals" [16]
So although many benefits are gotten by treating all skin types with the same parameters, it is becoming clear that adjustments should be made to account for bioindividuality.
Adjusted Dosing For Darker Skin Types
Here are a few studies and documents that advise adjusting the intensity, dose, wavelengths, and/or application mode (pulsed vs continuous) based on skin phototype.
One study recommends generally higher doses to reach deeper tissue targets:
"The clinical implication is that higher doses may be needed to deliver the same quantity of photons to the target tissue below the skin of persons with dark skin compared to those with light skin. Additionally, longer wavelengths may be more effective in treating deep lesion in individuals with darker skins.9,11" [17]
Another study notes that they increased the dose by 50% for people with dark skin in the trial:
"For dark residents with dark skin, the dose around the periphery was increased by 50%, as melanin absorbs photons and less is delivered to underlying tissue." [18]
In the Handbook of Low-Level Laser Therapy, authors Hamblin, de Sousa, and Agrawal comment that practitioners have observed less effectiveness treating wounds for darker skinned patients. They recommend increasing the dose by 25% and using pulsed modes to reduce heating. [19]
One study notes that the intensity was reduced by 50%, presumably to reduce superficial heating. However, it did not seem to increase the dose other than increasing the exposure time to deliver the same dose at the lower intensity (i.e. the exposure time would need to be doubled if the intensity was cut in half to reach the same dose).
"For patients with dark skin color, there is a pigment adjustment selection button on the laser console. When the pigment selection is activated, laser intensity is reduced by 50% and the software automatically recalculates the required dose." [20]
One study notes that for the lightest skin types the dose was decreased by 25% and for the darkest skin types the dose was increased by 25%:
"To address the possible effect of skin pigmentation on photon absorption, the Fitzpatrick Skin Type Scale (95) was used to determine skin type (pigmentation level), ranging from 1 (very fair skin) to 6 (darkest skin). The dose was adjusted when treating participants who had the lightest pigmentation, 1; or the darkest pigmentation, 6. Four participants had levels 1 or 6, and all others, in between. For those with the lightest skin, the treatment time/dose was reduced by 25%, and for those with the darkest, increased by 25%." [21]
One study comments that the recommendation is typically to increase the dose by up to 50% for darker skin types and decrease the dose by up to 50% for lighter skin types. However, they caution that this advice is "arbitrary", meaning it lacks evidence or substantiation. [8]
So we do have some clear guidelines that doses could be increased by 25-50% for the darkest skin types and even reduced by 25-50% for the lightest skin types. Reducing the intensity or using pulsing will also be helpful to reduce heat effects. However, many of these adjustments have not been well studied and standardized.
Heating and Safety:
With superficial absorption and melanin's excellent ability to convert photons into heat, then safety becomes an important factor for dark skin.
"Melanin takes in excessive light energy and converts it to heat in a process called absorption; heat is then dissipated into the environment as infrared radiation, thereby protecting the underlying skin." [22]
One laser study monitored the skin temperature response in patients with a range of skin phototypes. They found that typical powers and doses did not cause significant heating in the light and medium skin tones, however with the higher powered laser the people with darker skin types felt a pain response from too much heat.
"The significant heating of dark skin by the 200 mW, 810nm laser has implications for irradiation safety and clinical practice. There was three to sixfold increase in skin temperature in dark skin, reaching 42-43C, when compared with light and medium skin. This temperature corresponds to the thershold for painful thermal stimuli and was achieved even at small irradiation doses." [23]
Another study investigated the dosing limits based on skin types, and found that darker skin types had adverse events at lower doses than lighter skin types.
"Adverse events (AEs) included treatment-site erythema, hyperpigmentation, and blistering, all of which were mild and resolved without permanent sequelae.38 We concluded that LED-RL is safe up to 480 J/cm2 and may exert differential cutaneous effects depending on race and ethnicity, with darker skin being more photosensitive.38" [24]
Another study notes on the maximum intensity tolerated will be lower for people with darker skin types.
"Depending on the wavelength used, the upfront heat generated from absorption by melanin may be a dominant factor limiting the upper maximal limit of tolerable power intensity, particularly in darker pigmented individuals. " [25]
High intensities will cause more rapid heating which could lead to more adverse effects. Prolonged exposures and high doses are also correlated with more adverse effects.
This is why some clinicians are recommending reducing the intensity or using pulsed modes to reduce the heat. Near-Infrared wavelengths that will cause less heating compared to Red light will be more superficially absorbed by melanin.
Melanin Concentrations in The Skin
Melanin is a strong pigment for visible light, but does continue absorption into Near-Infrared range.
We often refer to this chart of the primary chromophores that cause superficial absorption in the skin.
The brown line in the chart above is the Melanin absorption coefficient spectrum. You can see it steadily decreases with longer wavelengths. However, it is clearly a strong absorber in the Red range and even into the NIR.
What this chart doesn't tell you is the concentration of melanin in the skin, only the coefficient of absorption.
A relevant study titled "Melanin Density Affects Photobiomodulation Outcomes in Cell Culture" tells us that the melanin concentration of the skin ranges from 0.008% (light skin) to 0.023% (dark brown). [26]
This is a 3 times difference in melanin concentration depending on Skin Phototype. The study concludes that the dosage for people with darker skin types will likely need to be higher especially for deeper tissue targets. [26]
Another study notes:
"Dark skin typically contains four‐ to sixfold more melanin" [5]
Another study describes the percentage of melanin found in the epidermis.
"Melanin can be found in the epidermis by approx. 3% for Caucasians, up to 16% for Mediterraneans and 43% for highly pigmented Africans [27]. " [27]
With such a significant range of melanin concentrations of the skin, we cannot ignore the role it could play in the efficacy of light therapies.
Optimal Wavelengths For Dark Skin Types
One study notes that for what they call "fair skin" the optical window of wavelengths is from 600nm to 1300nm. Which is consistent with the range typically referenced in PBM literature. [28]
However, the same study says for what they call "black skin" the optical window is restricted to 750nm to 1300nm. Meaning that the Red wavelengths are no longer part of the ideal optical window for darker skin phototypes. [28]
https://link.springer.com/chapter/10.1007/978-3-030-92880-3_3
The above study has a good graph on this phenomenon.
We can also make a graph from the human skin reflection data collected by the NIST.
Many will remember this graph is the reason why skin contact is preferred to reduce the reflection losses from Red and NIR light, which is substantial at about 60% for Caucasian skin.
However, for the darker skin group we see much less reflection in the Red (660nm) range, around only 40%. The difference of 20% is likely being absorbed superficially by melanin. Again confirming the superficial absorption of Red that will cause more of a heat effect.
It shows much more reflection in the 800's and 1050's where all phototypes become more similar. High reflection is a good thing, as it means there is a lack of superficial absorption and better penetration.
Another study concludes:
"the status of pigmentation should be taken into account for PBM using visible light (635 nm)." [2]
By now it should be clear that red wavelengths are not preferred to be used for people with dark skin types, as the "optical window" of wavelengths is clearly shifted.
Penetration of Wavelengths:
The penetration of wavelengths is substantially different depending on skin phototype.
One study finds up to 2 times less penetration in the darkest skin types compared to lighter skin types, even for 851nm light:
"Using the diffusion equation, Phan et al., determined the penetration of 851 nm light into varying skin-types and showed that light travelled the furthest through subjects with the palest skin pigmentation (ranging from approximately 1.8 mm – 4.75 mm amongst the 10 subjects) [65]. Light penetration was least for subjects with the darkest skin pigmentation, ranging from approximately 1.85 mm to 2.5 mm amongst 5 subjects." [29]
Another study noted a 24% decrease in penetration based on skin type with a 904nm laser.
"Over the range of Fitzpatrick scale values employed, from 2 to 6, there was a 24% decrease in energy transmission at this site. We calculated that for each Fitzpatrick scale point of skin pigmentation after a value of 2, there was a 6% decrease in energy transmission due to absorption by progressively darker skin colours." [8]
One study notes a drastically diminished light penetration (transmittance) with higher melanin concentrations with 635nm and 808nm laser. [3] With the 635nm having 60% less penetration and the 808nm having 30% less penetration.[2]
"As dark skin contains epidermic keratinocytes enriched with the melanin pigment, there was also less light transmittance of almost 60% and 30% after irradiation of 3.0 mm-thickness tissue with red and NIR light, respectively [77]." [2]
With a lack of penetration, this may be the reason why larger doses or exposure times will be needed to get adequate photons to the deeper layers of the body.
Cosmetic Laser Wavelengths for Dark Skin:
High intensity lasers are often used in dermatology clinics for skin resurfacing such as treating wrinkles, scars, acne, pigmentation, and tattoo removal.
These lasers are heating and ablative, essentially vaporizing surface layers of the skin or specific cells to promote regrowth. Often with downtime like skin redness for about 2 weeks after treatment. [30]
Since this is a high-intensity heat therapy with lasers, there has been a lot of work to distinguish optimal parameters based on Skin PhotoType, particularly to avoid adverse responses to people with darker skin types.
In contrast, Photobiomodulation is by-definition non-thermal and low intensity. This perhaps explains the lack of studies based on skin type for PBM. There hasn't been any urgency to adjust the dose for PBM because it does not pose an immediate safety risk.
However, we can certainly learn from these high-intensity laser studies to help inform us about optimizing PBM safety and dosing based on skin type.
One study titled "Laser photorejuvenation of Asian and ethnic skin" gives a good description of factors used to compensate for different skin phototypes.
They note:
"Since melanin absorption decreases exponentially with increasing wavelengths, lasers with longer and more deeply penetrating wavelengths generally produce safer and more reliable clinical results in dark skin (5)." [31]
Another study notes:
"Whereas early-generation lasers for hair removal and resurfacing were generally contraindicated for individuals with Fitzpatrick skin phototypes (SPT) IV–VI, advances in the past decade have given rise to a range of devices that can be safely used in ethnic skin. Longer wavelength lasers such as the 810 and 1064 nm Nd:YAG;" [32]
And another study tells us:
"We believe two wavelengths are generally appropriate for use in dark Latino skin, which include the Diode laser 810nm at low fluence and high repetition rate “in motion” (up to phototypes V) and Nd:YAG 1064nm (up to phototypes VI)" [33]
So this helps confirm why wavelengths like 810nm and 1064nm will be preferred to get adequate penetration and improve safety and effectiveness.
Melanin - an Active Chromophore?
Water absorption was once considered an inactive chromophore and merely a hinderance to penetration. However, thanks to relatively new research by Gerald Pollack on the understanding ot EZ (Exclusion Zone) Water, it is now recognized as not only an active chromophore for photobiomodulation mechanisms - but water absorption may be a dominant mechanism for PBM effects.
Even blood absorption is now appreciated to have a more active role in Photobiomodulation by virtue of the recent discovery of cell-free mitochondria in the blood.[34] So again, once considered a hinderance to penetration, blood absorption is credited to play a role in systemic mechanisms of photobiomodulation.
Similarly, we have yet to discover if Melanin can play any active roles in photochemical responses by light absorption. The heat generated by the melanin absorption may confer some benefits as long as it is not burning.
Many organisms utilize melanin, and it seems to perform many more functions than merely protection from light.
"No other natural polymer is characterized by so many intriguing properties and is able to fulfill such a wide variety of different functions as eumelanin (called henceforth EU), which is the dark-brown/black component of the melanin family. " [35]
Neuromelanin is a type of melanin found in the brain. It seemingly has no business being there. However, neuromelanin clearly serves important brain functions since we know that the loss of this brain pigment is correlated with the progression of Parkinson's disease. [36]
A 2014 article titled "The role of human photosynthesis in predictive, preventive and personalized medicine" discusses the possibility that melanin can create energy as a kind of photosynthesis in humans and animals. [37]
A 2008 article titled "Melanin directly converts light for vertebrate metabolic use: Heuristic thoughts on birds, Icarus and dark human skin" references the paradox of migratory birds making long flights despite an apparent lack of energy sources. They also believe melanin to be providing energy from light to sustain the patterns of these birds. [38]
However, other articles have dubbed this theory of melanin producing energy as a kind of photosynthesis in animals and humans as pseudoscience. [39]
A real scientific phenomenon is the ability of melanated "melanopic" mushrooms to grow in highly radioactive environments like Chernobyl, as one paper titled "Melanin, Radiation, and Energy Transduction in Fungi" describes. This paper does confirm the mushroom's melanin is able to convert the radiation into a useful energy for their metabolism.[40]
With melanin being a unique light absorber with many enigmatic functions in living organisms, it will not be surprising if we do find an active role it plays in PBM in the future.
Summary:
Red and Near-Infrared light therapy has the ability to help the health of all people. As always, to optimize the benefits of red light therapy for the individual is to appreciate the many aspects of bioindividuality.
The concentration of melanin in human skin is widely varied. As it is naturally a strong pigment for absorbing light, it plays an important role in how we implement light therapies.
Responsible usage of Red Light Therapy is safe and effective for all skin types. But, it is clear that the parameters should be adjusted to optimize the outcomes.
For darker skin types it may be ideal to increase the dose by 25-50%, prefer NIR wavelengths over Red, and reduce the intensity or use pulsing to reduce heating.
And vise-versa, people with the lightest skin types can tolerate higher intensities, both Red&NIR light, however may do well with lower doses due to higher penetration of the light.
There is still much to understand about the intracies of how Red and NIR light interacts with the body.
However, we do have a lot of evidence right now to help improve outcomes for more people.
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Water Absorption Coefficient Spectrum:
https://omlc.org/spectra/water/data/hale73.txt
https://omlc.org/spectra/water/abs/
[42]
Hemoglobin Absorption Coefficient Spectrum:
https://omlc.org/news/jan98/skinoptics.html
https://omlc.org/spectra/hemoglobin/summary.html
[43]
Melanin Absorption Coefficient Spectrum: