Across the world, there is great diversity in skin color. Across this array of skin colors, there are many disorders related to skin pigmentation such as post-inflammatory hyperpigmentation (PIH), sun spots, and melasma. But why do those with darker skin color are more prone to pigmentation issues?

The skin is a complex organ with the primary role of protecting the body from external threats such as UV rays, dirt, microorganism, and toxins. When the skin receives insults and becomes inflamed, it immediately springs into action to defend itself. Exposure to UV radiation, heat, or other forms of trauma that results in inflammation will trigger an immune response from the skin. One form of defense the skin has is the production of melanin, a dark pigment that absorbs UV radiation. Those with darker skin tones have melanocytes that are more active thereby producing more melanin than those with fair skin. It is important to understand that all humans have roughly the same amount of melanocytes. Skin color variations are due to melanocytes productivity in making melanin.

New research leveraging advanced imaging technology has enabled a more specific understanding of the skin biochemistry. Research conducted by Dr. Sriwiriyanont and colleagues shows that inflammation may result in hyperpigmentation through several mechanisms. One example is inflammatory mediators such as IL-1-α, endothelin-1, and/or stem cell factor directly stimulate melanocytes to produce melanin (Sriwiriyanont et al., 2006; Unver et al., 2006). Another mechanism discovered is reactive oxygen species such as peroxides, superoxide, and hydroxyl radical induce epidermal cells to release of endocrine inducers of pigmentation, such as an α-melanocyte-stimulating hormone. Melanin produced during an inflammatory event can enter the dermis layer of your skin and get engulfed by macrophages to become “melanophages”. Melanophages in the dermis often stubborn and tend to stay for a much longer duration than melanin. Therefore, post-inflammatory hyperpigmentation typically is long-lasting and highly difficult to remove.

When dark skin becomes inflamed, a combination of the mechanisms described above triggers melanocytes to produce more melanin. Dark skin has a natural high baseline of melanin production and when stimulated, it’s rate of melanin production can increase much faster than that of light skin. Therefore, dark skin has a greater risk for hyperpigmentation as a response against any form of skin trauma.

Treatments of pigmentation concerns have long used hydroquinone. However, due to cytotoxicity concerns, hydroquinone has been banned in Europe and Japan. New insights into the mechanisms of melanin induction will lead the way to newer and less toxic approaches to treating pigmentation.

Reference:

Journal of Investigative Dermatology Symposium Proceedings
Volume 13, Issue 1, April 2008, Pages 10-14
Latest Insights into Skin Hyperpigmentation

Modern Pathology
September 2001
Morphologic Features of Melanocytes, Pigmented Keratinocytes, and Melanophages by In Vivo Confocal Scanning Laser Microscopy

Lab Investigation, 86 (2006), pp. 1115-1125
Sriwiriyanont, A. Ohuchi, A. Hachiya, M.O. Visscher, R.E. Boissy
Interaction between stem cell factor and endothelin-1: effects on melanogenesis in human skin xenografts