· skincare · 6 min read

The science behind your skin hyperpigmentation

Let me guess! probably at some point in your life, you got inflamed breakouts, and after treating them they started fading away. You thought for a second that it was all over but then dark spots appeared where the inflamed acne was nesting. This is post-inflammatory hyperpigmentation (PIH) so let's understand it and its underlying mechanism to manage it better.

PIH is one of the dyschromic disorders that occur after inflammation or cutaneous injury (like acne lesions) in all skin phototypes, but it’s mainly a hallmark of dark-skinned individuals (Fitzpatrick skin phototypes III to VI).

Types of PIH:

There is an epidermal, dermal, and mixed dermal-epidermal hyperpigmentation based on the location of the pigment.

  • Epidermal PIH: light to dark brown spots
  • Dermal PIH: grey to blue spots

How does the PIH develop?

First of all, we should know that the PIH mechanism involves two types of cells:

  • Keratinocytes: They are abundant in all layers of the epidermis (the outermost skin layer) and produce keratin to protect epithelial cells from all types of stress and hold the skin cells and layers together.
  • Melanocytes: They are located in the basal layer of the epidermis and secrete a protective pigment against UV rays; melanin.

PIH develops locally in areas of previous inflammation. In fact, due to skin inflammation melanocytes react differently depicting increased activity, hyperplasia, and hypertrophy. In cutaneous inflammation, cytokines and other inflammatory mediators are released such as Tumor Necrosis Factor (TNF-alpha), and interleukins… These mediators stimulate abnormal epidermal melanogenesis. In the melanocytes, the excess melanin is synthesized from tyrosine within melanosomes (intracellular organelles found in melanocytes and within which the melanin is made and stored). Then via melanocytes dendrites, the melanosomes transport the melanin to the keratinocytes. You can read more about this here 1.

This excess of melanin in keratinocytes exhibits epidermal hyperpigmentation, but it can develop into deeper dermal hyperpigmentation. How? Inflammation is among the factors that damage the basal keratinocytes. Once the damage takes place, it facilitates the melanin to be phagocytized by macrophages which form dermal melanophages. The melanin will be released in the dermis which causes the grey to blue coloration and which may be permanent.

You have to know that both epidermal and dermal PIH can occur within the same inflamed injury, and that epidermal PIH is more prone to resolution than dermal one because the available topical treatments do not target the melanophages involved in the dermal hypermelanosis.

Another mechanism by which PIH occurs is that inflammation stimulates the generation of eicosanoids (lipid-based signaling molecules) from cell membranes and they include Prostaglandins E2 and D2, leukotrienes B4, C4, D4, and E4, and thromboxanes B2. Leukotriene C4 increases tyrosinase activity and this means increasing melanogenesis from the substrate tyrosine 2.

How to make your PIH fade away?

You have to bear in mind that epidermal PIH lasts from months to years after the cutaneous inflammation has occurred whereas the dermal PIH may be permanent. Don’t feel discouraged because if the underlying inflammation is treated properly, then the PIH can be asymptomatic. You also need to be patient because expecting results only after a few weeks of applying treatments is not enough. It’s a marathon, not a sprint. Focus on applying your products meticulously and consistently, and make sure to invest in good-quality sunscreens.

  • Photoprotection: UV and visible light (VL) are very dangerous as they exacerbate PIH. Thus, applying sunscreen with an SPF ≥ 30 can be a game changer. Sunscreens with zinc oxides are very effective in preventing the destructive effect of sun rays. Moreover, iron oxides in tinted sunscreens are very efficient as well in blocking UV rays and VL so say goodbye to the myth that says tinted sunscreens are not photoprotective. my tip to you is to invest in an SPF 50 sunscreen and reapply it regularly every two hours.

  • Hydroquinone: it will block the tyrosinase enzyme that catalyzes the synthesis of excess melanin. OTC hydroquinone is available in 2% and prescribed by physicians with a percentage of 4%. Hydroquinone has several adverse effects such as stinging, face swelling, inflammation, and rashes… You should know that applying hydroquinone on normal skin will cause hypopigmentation and you definitely should apply sunscreen like crazy I would say to prevent any side effects.

  • Hydroquinone, retinoid, corticosteroid combination: This triple combination cream (TCC) therapy is effective in reducing PIH, and with which the effect of hydroquinone is way better than using it by itself. Retinoids decrease melanosome transfer whereas corticosteroids suppress non-selectively melanogenesis. side effects like erythema and peeling may be observed.

  • Azelaic acid, niacinamide, vitamin C, kojic acid, bakuchiol, arbutin, and thiamidol: These are natural compounds found in different cosmeceutical products and share the ability to decrease and stop the tyrosinase activity which puts end to the hypermelanosis. These compounds can be found together in various OTC cosmeceuticals. They have also a noticeable effect of scavenging reactive oxygen species. Remember that with azelaic acid you have to aim for a minimum 15% concentration to fade the pigmentation. Anything lower than 15% is just useless to buy.

  • Tranexamic acid (TXA): Topical TXA (2% to 3%) has been shown to be effective in treating PIH when combined with 1% kojic acid and 5%niacinamide, or combined with niacinamide alone. TXA reverses UV-induced hyperpigmentation by inhibiting the binding of plasminogen to the keratinocytes reducing the melanocyte tyrosinase activity and leading to a decrease in inflammatory mediators secretion such as prostaglandins. Overall, TXA efficacy is still a topic of debate about its efficiency in treating PIH.

To satisfy your curiosity, you can read about the mechanisms of action of the previously mentioned active ingredients here 3.

Sunscreen usage + topical treatments are the first lines of therapy before shifting to oral treatments. In the upcoming articles, I will dive deeper into each active ingredient and suggest products to purchase that can alleviate selectively your PIH so stay tuned.

PS: You are beautiful the way you are! love yourself first because it’s the best placebo effect you can ever experience.

  1. Moreiras, H., Seabra, M. C., & Barral, D. C. (2021). Melanin Transfer in the Epidermis: The Pursuit of Skin Pigmentation Control Mechanisms. In International Journal of Molecular Sciences (Vol. 22, Issue 9, p. 4466). MDPI AG. https://doi.org/10.3390/ijms22094466

  2. Silpa-archa, N., Kohli, I., Chaowattanapanit, S., Lim, H. W., & Hamzavi, I. (2017). Postinflammatory hyperpigmentation: A comprehensive overview. In Journal of the American Academy of Dermatology (Vol. 77, Issue 4, pp. 591–605). Elsevier BV. https://doi.org/10.1016/j.jaad.2017.01.035

  3. Ko, D., Wang, R. F., Ozog, D., Lim, H. W., & Mohammad, T. F. (2023). Disorders of hyperpigmentation. Part II. Review of management and treatment options for hyperpigmentation. In Journal of the American Academy of Dermatology (Vol. 88, Issue 2, pp. 291–320). Elsevier BV. https://doi.org/10.1016/j.jaad.2021.12.065

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