We see colored objects because they absorb visible light, and they have the color of the wavelengths that are reflected (and obviously are not absorbed). For instance, blue objects do absorb—more or less—red and yellow light. When a molecule absorbs light, one of its electrons becomes “excited.” When it is in such a state, it is bound less tightly to the molecule itself and is more prone to form bonds with surrounding molecules. This is the basic principle of photochemistry.

It can also happen that the excited molecule transfers its energy or the electron itself, to nearby acceptor molecules. When this occurs, it leads to the formation of a few reactive oxygen species (ROS) such as singlet oxygen (¹O₂­) or the Superoxide ion (O^2-).

Light and Life

As for everything else, both the toxicity and healing powers depend on the dose and on the site of administration. For example, we know that drugs can be beneficial in treating an organ, but they can have negative side effects in another organ. For instance, some drugs can be beneficial against inflammation and can still be toxic for the kidney. 

Chromophores’ Role

The same is true for visible light. 

For light to be “active,” it is necessary that there be, somewhere, a molecule able to absorb photons. Such molecules are called chromophores and are widely present in nature. The one that is perhaps the most abundant on the surface of the earth is chlorophyll, the molecule in plant cells that absorbs light from the sun and uses its energy to convert carbon dioxide and water into glucose and oxygen. 

And this is the reason why the rainforest can be helpful in reducing the excess carbon dioxide in the atmosphere. Other chromophores of interest are the linear tetrapyrroles that trigger photo movement in plants. 

In vertebrates, the rods and cones in the retina harbor the chromophores that allow vision to take place. When exposed to very intense illumination, the chromophores in the eye can be overwhelmed and temporary blindness can ensue. Damage to the retina by light depends on the intensity and on the wavelength of the light.

Light and Skin

Intense blue light, for instance, can damage the retina, but turns out to be quite effective in killing the bacterium Propionibacterium acnes, a microorganism that grows anaerobically in clogged pores and provokes the formation of the so-called pimples with the consequent fastidious inflammatory reaction. 

Since the treatment of acne with retinoic acid and antibiotic can have severe side effects, a non-invasive treatment such as blue-light phototherapy might be of extreme interest for acne patients.

As a matter of fact, P. acnes produces and releases orange molecules called Porphyrins that, upon absorbing blue photons, transfer their excitation energy to nearby oxygen molecules that so acquire the status of singlet oxygen, the most reactive, and therefore the most incredibly toxic of all the known ROS. 

So, when a P. acnes cell is exposed to blue light, the Porphyrins it contains catalyze the formation of singlet oxygen and the bacterium dies because it is being poisoned from within!

The published results relative to the efficacy of blue-light therapy of acne are surprisingly inconclusive so that the literature does not provide a clear-cut answer to the question: is blue-light therapy recommended for acne? 

Treating Acne

Some scientists have realized that the high extinction coefficient for blue light of the porphyrins might limit the penetration of blue photons in the skin. Porphyrins harbored by those P. acnes bacteria sitting on the top of the pores might hinder blue photons from reaching those bacteria niched more deeply in the pores. 

Realizing that porphyrins do also absorb red photons, albeit at lower rate, some scientists have undertaken to treat Acne vulgaris with a phototherapy consisting of red photons and blue photons. 

The reported results indicate that in a study with 24 patients, after four weeks of alternate blue light-red light treatment, the final improvements in non-inflammatory and inflammatory lesions were 34.28% and 77.93%, respectively.¹ 

In another study where 22 patients completed the trial, the reduction of lesions after four weeks was 46% and after 12 weeks the mean lesion count reduction was 81%  with p=0.001.² In a third study, red and blue light were administered in different ways to two groups of patients: one group received alternating blue (470nm) and red (640nm) light in two visits a week for four consecutive weeks, while the other group got blue- and red-light treatments consecutively on the same visit for four consecutive weeks. During the study period, conventional treatments were prohibited. 

There was no difference between the results obtained following the two regimens. Marked improvement were observed only for inflammatory lesions. There were no side effects noted throughout the study period.³

Conclusion

These results seem to provide supporting evidence to justify the manufacture of specific masks equipped with light emitting diodes (LED) able to cast red and blue light on the skin of the persons wearing them. 

“LED light therapy is actually a NASA technology that was adopted by the skincare community when its ability to heal wounds and tame inflammation was noticed,” explained Kathryn Shaffer, School of Dermatology. “Blue light frequencies are typically used to treat acne, while red light is used for anti-aging concerns. If shooting lights at your face sounds scary, you should know that there are no ultraviolet rays in these devices.”⁴

References

1. Lee SY, You CE, Park MY. Blue- and red-light combination LED phototherapy for acne vulgaris in patients with skin phototype IV. Lasers Surg Med. 2007 Feb;39(2):180-8. doi: 10.1002/lsm.20412. PMID: 17111415.
2. Goldberg DJ, Russell BA. Combination blue (415 nm) and red (633 nm) LED phototherapy in the treatment of mild to severe acne vulgaris. J Cosmet Laser Ther. 2006 Jun;8(2):71-5. doi: 10.1080/14764170600735912. PMID: 16766484.
3. Nitayavardhana S, Manuskiatti W, Cembrano KAG, Wanitphadeedecha R. A Comparative Study Between Once-Weekly and Alternating Twice-Weekly Regimen Using Blue (470 nm) and Red (640 nm) Light Combination LED Phototherapy for Moderate-to-Severe Acne Vulgaris. Lasers Surg Med. 2021 Oct;53(8):1080-1085. doi:
4. https://schoolofdermatology.com/pages/7-led-light-therapy-masks-that-will-not-suprise-your-dermatologist?gc_id=17277716811

Paolo Giacomoni, PhD

Insight Analysis Consulting
paologiac@gmail.com
516-769-6904

Paolo Giacomoni acts as an independent consultant to the skin care industry. He served as Executive Director of Research at Estée Lauder and was Head of the Department of Biology with L’Oréal. He has built a record of achievements through research on DNA damage and metabolic impairment induced by UV radiation as well as on the positive effects of vitamins and antioxidants. He has authored more than 100 peer-reviewed publications and has more than 20 patents. He is presently Head of R&D with L.RAPHAEL—The science of beauty—Geneva, Switzerland.