Acne vulgaris is a common inflammatory skin disorder occurring often in adolescent years and can have a profound impact on the patient’s wellbeing.
In addition, it has the potential to cause scarring which can further compound the psychological burden. (1) Increasingly, acne is seen and reported in different age groups and with varying clinical presentations.
There are a large number of laser and light-based therapies available to patients for “common” acne, also known as acne vulgaris. However, these are not without side effects and in many cases the disease can be resistant to treatment, with relapses are relatively common. Current treatment options available include topical therapy (both over the counter and prescriptive), chemical peels, and systemic therapy in the form of tablets. The choice of treatment depends on a number of factors such as the severity grade, type of lesions present, anatomic location, and patient preference. (2)
Of late, interest in lasers and other light-based treatments has increased, with some authors reporting encouraging findings. One of the main advantages of the use of lasers in acne is the high degree of compliance and the negligible rate of potential systemic adverse events. (3) It is therefore an attractive choice to many patients who are either unwilling to commit to prescriptive therapies or have experienced undesirable side effects.
It must be noted that while lasers certainly play a role in the management of acne, it is not the first-line choice of treatment, and in my opinion, works better synergistically in combination with other treatments. It is suitable for mild-to-moderate severity acne and is not recommended for severe acne.
Mode of action
Prior to explaining the mode of action of lasers in acne it is useful to briefly revisit the pathogenesis of acne and the main factors involved in its prognosis and treatment. Acne is a disease arising from the pilosebaceous unit, which comprises of the hair follicle with the attached sebaceous glands and the follicular openings often referred to as pores. Four key mechanisms play a role in acne and include: overactivity of the sebaceous gland, often manifesting itself with oily skin, follicular hyperkeratinisation, manifesting itself with blockage of pores, overgrowth of a commensal gram-positive bacteria cutibacterium acnes (formerly known as p.acnes); and lastly an inflammatory response mediated largely by the innate immune system secondary to the presence of the bacteria and the excessive sebum production. (1)
It is well known that the innate system plays a key role in acne, when pattern recognition receptors called T-like receptors-2 are activated with mediators such as AP-1 and NFĸB eliciting an inflammatory response. (4) Successful treatment of acne therefore should target as many of these mechanisms as possible, and therefore combination therapy is often recommended.
Lasers and light-based therapies such as light-emitting diodes (LED) and intense pulsed light (IPL) work predominantly through a combination of photochemical and photothermal mechanisms. That is, the heat generated from the light can have beneficial effects on acne through effects on sebaceous gland activity, bactericidal killing and anti-inflammatory actions through heat shock proteins. Photochemical effects are largely aimed at the c.acnes bacteria through a phototoxic reaction, with further modulations of the inflammation through the biological interaction of light and tissue. (3)
Endogenous porphyrins produced by c.acnes are thought to absorb light at specific wavelengths which then produce phototoxic effects, resulting in bacterial death with, as result, a reduction in the secondary inflammation partly initiated by the overgrowth and presence of the bacteria. Another example of the photochemical effect is the alteration in the TGF-beta following the use of pulsed-dye laser (PDL) in acne. (5) In general, all lasers and light-based therapies have shown a preferential benefit in inflammatory acne compared to non-inflammatory comedonal acne and as such, lasers should not be recommended if the acne is predominantly non-inflammatory.
Main modalities
Each of the main laser or light-based modalities will be presented with regards to its role in acne:
LED (blue and red light)
Although blue light has poor skin penetration given its short wavelength in the range of 400-420nm, it exhibits the strongest porphyrin photo-excitation co-efficient and thus is the most effective wavelength to photo-activate the endogenous porphyrins produced by c.acnes. Pulsed blue light is not used in clinical practice hence LED is the preferred choice for this wavelength. The difference is that LED contains a band of wavelengths within the blue light spectrum, emitting continuous low-level energy light in a non-collimated fashion. There are several studies on blue light in acne as monotherapy or in combination, with most studies showing an improvement with photodynamic therapy (PDT) and blue light showing the strongest level of evidence. (6)
Red light penetrates the skin at a deeper level – down to the sebaceous gland – and is thought to have anti-inflammatory properties. Its deeper penetration is also clinically relevant in targeting the sebaceous glands and the micro-vessels around them. Currently the evidence of red light is the strongest in combination with blue light, topical therapy, or with a photosensitising drug as PDT. (7)
Pulsed dye laser (PDL)
The 585/595nm PDL targets oxyhaemaglobin and results in selective photothermolysis of vessels. It is largely considered the gold standard laser in vascular malformations and disorders largely owing to the vast level of evidence behind it. In acne the PDL has been used with overall good level of success both as monotherapy and in combination. The mechanisms are a combination of photothermal effects and in particular the microvessels that form part of the inflammatory process in addition to photochemical effects and bactericidal killing, as described earlier in the article.
This is because of the absorption spectrum of endogenous porphyrins with their peak in blue light and a second lower peak in the soret band between 500 and 600nm, hence the effect of the PDL. There are different parameters used with inconclusive evidence for one particular range and both purpuric and non-purpuric settings in acne showed comparable efficacy. (15)
Potassium titanyl phosphate (KTP)
This 532nm laser emits green light which penetrates deeper than blue light but less so than PDL for the same spot size. Given its wavelength within the soret band it exerts similar mechanisms to the PDL although with fewer studies and comparative trials.
Nevertheless, it has been used with success in acne and like the PDL works preferentially in the inflammatory type of acne. (3)
Infrared lasers
Infrared lasers penetrate deep into the dermis, targeting water as their main chromophore with a predominantly photothermal effect on the sebaceous glands in addition to the generation of heat-shock proteins that can lead to bacterial killing. A previously used laser with 1450nm was specifically designed for acne with good efficacy, although this is no longer being manufactured. (8)
The 1540nm erbium glass laser is a mid-infrared laser; its wavelength is absorbed primarily by water and thus targets the sebaceous glands and dermal matrix. There is minimal absorption by melanin, making it a safe option in dark-skinned patients. While it is predominantly used for scars and rejuvenation, there are few studies supporting its benefit in acne. (9)
The 1064nm Nd:YAG is probably the best studied and used infrared laser in acne, which similarly to the other modalities, has shown superiority in the inflammatory component with overall satisfactory results following few treatment sessions. Comparative studies have demonstrated comparable results to the PDL with few side-effects. The mode of action is predominantly photothermal and both the long-pulsed in millisecond as well as the microsecond modes have been used with equivocal efficacy. (3)
Photodynamic therapy (PDT)
Photodynamic therapy includes the use of a photosensitiser, which is taken up by the pilosebaceous unit and undergoes metabolism through the haem-synthesis pathway, resulting in the production of protoporphyrin IX. The activation of this pathway leads to the production of free radicals and singlet oxygen which are cytotoxic, thus destroying the pilosebacoues unit and killing c. acnes itself. (10)
For PDT to be effective, light, oxygen and a photosensitiser are required. A light source can be an LED or fluorescent lamp, laser, sunlight, xenon flash lamp, arc lamp or filtered incandescent lamps. C. acnes photo-inactivation can be altered depending on the concentration of porphyrins, which is governed by the type of acne lesion, effective fluence, wavelength of the photons emitted, exposure time and the temperature. Currently, most of the PDT is used in the setting of blue and red light with the highest level of evidence.11 Studies on PDT with IPL and PDL have however shown good results, albeit less compared to LEDs. (12)
Intense pulsed light
An IPL device delivers an intense source of light, the wavelengths of which can be modified via the use of filters. It is different to lasers in that the light is non-collimated and a band of wavelengths are used instead of a single wavelength. The theory of treating acne lesions with IPL is based on the photochemical and photothermal effects on both the c. acnes as well as the inflammatory process, sebaceous glands, and small vessels associated with the process.
Different filters are used either in the blue light range, soret band (500-600nm), or infrared. Some IPL machines have a dedicated “acne-filter” handpiece, emitting shorter wavelengths in blue and visible light with longer wavelengths in the infrared range to allow for maximum dual effect of both photochemical and photothermal effects at different depths. IPL is generally effective in acne and can be used in combination with other treatments. (13)
Photopneumatic therapy
Photopneumatic therapy combines pneumatic energy in the form of suction and broadband light (400-1200nm), encompassing the short blue light wavelengths and the longer infrared wavelengths with the advantages explained above. The suction acts to lift the contents of the dermis, bringing it closer to the skin’s surface, thus making energy transfer more effective. There is also an element of comedone clearance through the mechanical suction. This treatment is relatively safe with few studies supporting its efficacy in mixed inflammatory and comedonal acne, the latter in particular secondary to the pneumatic function. (14)
Combination therapy
As mentioned, while light-based therapies are largely effective in acne they are best used in mild-to-moderate severity cases, and preferably in combination. Appropriate skincare products suitable for acne such as salicylic or glycolic acid exfoliators or cleansers with topical niacinamide or retinoids can be combined with lasers for enhanced efficacy. Systemic drugs can be combined, although in most cases caution is required, and this would be limited to the experienced practitioner.
My preferred method is the PDL in lighter skin types (or the IPL) and the Nd:YAG in darker skin types to maximise safety. I prefer to combine the laser or IPL treatments with appropriate topical therapy and use at intervals of two to three weeks, with the exception of LED therapy, which is more frequent.
Lasers and light-based therapies appear to work better on the inflammatory component and require several treatment sessions based on the severity. They are a suitable choice for patients unwilling to or unsuitable for standard medical therapy and are generally safe. The main advantage is the lack of systemic side-effects, which is increasingly requested by patients.
Dr Firas Al-Niaimi is a consultant dermatologist, Mohs and laser expert with over 15 years’ experience. He is currently in full-time private practice in London alongside a lecturing and research post at a Danish university involved in scientific research. Dr Al-Niaimi has published over 180 publications in dermatology and lasers.
References
1. Zaenglein AL. Acne Vulgaris. N Engl J Med. 2018;379(14):1343-1352.
2. Nast A, Dréno B, Bettoli V, et al. European evidence-based (S3) guidelines for the treatment of acne. J Eur Acad Dermatol Venereol. 2012;26 Suppl 1:1-29.
3. Tong LX, Brauer JA. Lasers, Light, and the Treatment of Acne: A Comprehensive Review of the Literature. J Drugs Dermatol. 2017;16(11):1095-1102.
4. Dreno B, Gollnick HP, Kang S, et al. Understanding innate immunity and inflammation in acne: implications for management. J Eur Acad Dermatol Venereol. 2015;29 Suppl 4:3-11.
5. Seaton ED, Mouser PE, Charakida A, Alam S, Seldon PM, Chu AC. Investigation of the mechanism of action of nonablative pulsed-dye laser therapy in photorejuvenation and inflammatory acne vulgaris [published correction appears in Br J Dermatol. 2007 Feb;156(2):409.
6. Scott AM, Stehlik P, Clark J, et al. Blue-Light Therapy for Acne Vulgaris: A Systematic Review and Meta-Analysis. Ann Fam Med. 2019;17(6):545-553.
7. Posadzki P, Car J. Light Therapies for Acne. JAMA Dermatol. 2018;154(5):597-598.
8. Darné S, Hiscutt EL, Seukeran DC. Evaluation of the clinical efficacy of the 1,450 nm laser in acne vulgaris: a randomized split-face, investigator-blinded clinical trial. Br J Dermatol. 2011;165(6):1256-1262.
9. Politi Y, Levi A, Enk CD, Lapidoth M. Integrated cooling-vacuum-assisted 1540-nm erbium:glass laser is effective in treating mild-to-moderate acne vulgaris. Lasers Med Sci. 2015;30(9):2389-2393.
10. Pollock B, Turner D, Stringer MR, et al. Topical aminolaevulinic acid-photodynamic therapy for the treatment of acne vulgaris: a study of clinical efficacy and mechanism of action. Br J Dermatol. 2004;151(3):616-622.
11. Boen M, Brownell J, Patel P, Tsoukas MM. The Role of Photodynamic Therapy in Acne: An Evidence-Based Review. Am J Clin Dermatol. 2017;18(3):311-321.
12. Rojanamatin J, Choawawanich P. Treatment of inflammatory facial acne vulgaris with intense pulsed light and short contact of topical 5-aminolevulinic acid: a pilot study. Dermatol Surg. 2006;32(8):991-997.
13. Taylor M, Porter R, Gonzalez M. Intense pulsed light may improve inflammatory acne through TNF-α down-regulation. J Cosmet Laser Ther. 2014;16(2):96-103.
14. Omi T. Photopneumatic technology in acne treatment and skin rejuvenation: histological assessment. Laser Ther. 2012;21(2):113-123.
15. Forbat E, Al-Niaimi F. Nonvascular uses of pulsed dye laser in clinical dermatology [published online ahead of print, 2019 Apr 19]. J
