Pollution as a Risk Factor for the Development of Melasma and Other Skin Disorders of Facial Hyperpigmentation ‑ Is There a Case to Be Made?

Melasma is a complex disorder, often refractory to treatment, emotionally distressing, and associated with a decreased quality of life. Pollution may work synergistically with other factors such as genetics, cumulative ultraviolet and visible light exposure to stimulate melasma. Pollution may be an important puzzle piece for the medical management of melasma. Targeted efforts to reduce skin pollution may be considered in the overall treatment plan. We currently recommend sun avoidance, sun protection, use of physical sunscreens, and antioxidants. In addition, we may need to counsel our patients regarding the cleansing and neutralization of environmental pollutants from the skin. This is the first cited published article that links pollution as a possible etiologic factor for melasma. If supported, this may also apply to other refractory disorders of facial hyperpigmentation with a unique geographic predilection. Further global investigations are needed to add to our body of knowledge and validate or not, this clinical hypothesis. A PubMed search was performed using keywords: Pollution, Polycyclic Aromatic Hydrocarbons, Oxidative stress, Extrinsic Aging, and Melasma.

Worldwide pollution is a major health concern. There is accumulating scientific evidence that pollution plays an important role in extrinsic aging skin.^1,2 This article invites the reader to consider pollution as a possible emerging etiologic factor synergistic with established risk factors for development of melasma and other facial pigmentary dyschromias. Air pollution in the form of airborne particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) enter the skin via nanoparticles.

Lademann proposed that long term exposure to PM-bound PAHs nanoparticles may lead to skin entrance either through the hair follicle or transepidermal absorption.³ These nanoparticles generate quinones. Quinones are redox-cycling chemicals that produce reactive oxygen species (ROS), which target mitochondrial DNA.^4,5 The PM increases the amount of reactive oxygen species which increases the metalloproteinases and leads to extrinsic aging, which includes skin pigmentation.⁶ It has been noted that skin pigmentation may be induced in the absence of UVR.⁷ Krutmann et al demonstrated PAH’s to induce melanocytic proliferation in mice.⁸ This may shed light on why some Asians who are diligent about sun avoidance develop solar lentigines on sun protected skin.⁹ The incidence of some disorders of facial hyperpigmentation specifically, melasma, is highest in individuals of skin type III-VI living in India and Southeast Asia.^{10- 13} These are interestingly also geographic regions with very heavy pollution. India, Southeast Asia, China and United States are world leaders in pollution.¹⁴ Given the evolving body of evidence of the role of PAH with extrinsic aging, it is not unreasonable to propose that pollution may have a role in the development of melasma and other pigmentary dyschromias such as periorbital hyperpigmentation and solar lentigines. Drakaki et al categorized pollutants which affects the skin (Figure 1).¹⁵ 1) Particulate matter (PM) consisting of airborne particles in solid or liquid form. PM includes aerosols, smoke, fumes, dust, ash and pollen. 2) Polycyclic Aromatic Hydrocarbons (PAHs), which originate from woodburning, combustion of organic material including vegetative combustion, charred meats, coal burning, and cigarette smoke. We have long associ-