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Définition et cause de l'hyperpigmentation post-inflammatoire.

Post-inflammatory Hyperpigmentation (PIH): Definition and Causes.

Some skin traumas require such an anti-inflammatory response that they leave dark spots known as post-inflammatory hyperpigmentation (PIH). What biological mechanism lies behind them? What is PIH? Do these spots only appear after acne breakouts, or are there other causes? Here's the lowdown.

What Is PIH?

Sometimes called hyperpigmented scars, these marks are a type of hyperpigmentation. They appear as persistent flat brown or black spots (see photo above), depending on skin color.

As the name suggests, PIH appears following an inflammatory response in the skin, which can be triggered by acne flare-ups, atopic dermatitis, psoriasis, certain aesthetic treatments (dermabrasion, chemical peels and laser treatment) or even injury.

They are due to increased melanin production in response to the inflammatory reaction in question. In fact, the appearance of these hyper-colored areas relies on the production of inflammatory cytokines, with pigmentogenic properties, by the surrounding cells. These cytokines activate melanocytes (melanin-producing cells), leading to a major release of melanosomes (pigment granules) and thus surplus melanin.

Although this phenomenon can affect all skin types, it is generally more frequent in people with mixed to dark skin (phototypes IV to VI). Indeed, these subjects contain more melanin and their melanosomes are more reactive. In addition, a 2016 study found that post-inflammatory hyperpigmentation resulting from acne breakouts takes a long time to go away – at least 1 year for more than half the subjects surveyed, and up to 5 years for some. The majority of patients also reported that this hyperpigmentation is as bothersome, if not more so, than the acne itself.

Post-inflammatory Hyperpigmentation: Accentuated by UV Rays.

When the cutaneous barrier is damaged by inflammation of any kind (acne, injury, disease…), the healing zone is the thinnest and most fragile part of the skin. It is therefore all the more vulnerable to the sun's UV rays. If you expose the irritated area to the sun, the skin will overreact to protect itself, recruiting large quantities of pro-inflammatory molecules such as cytokines. The result: excessive, localized melanin production, which further contributes to the appearance of post-inflammatory hyperpigmentation.

What's more, a 2015 study demonstrated that effective sun protection can reduce the appearance of PIH. Participants were randomly assigned to receive SPF30 or 60 sunscreen applied daily for 8 weeks during the summer. Results showed a lightening of pre-existing hyperpigmented spots in 81% of patients, and a reduction in the number of spots in 59% of patients. What's more, those using the SPF60 sunscreen showed greater improvements in the overall lightening of brown spots than those using the SPF30 sunscreen. However, the lack of control is a limiting factor in this study.

In any case, make sure you protect yourself from the sun on a daily basis by applying a broad-spectrum SPF sunscreen, and limit your exposure to the sun as much as possible. To protect yourself from the sun's UV rays, choose one of our body or face sunscreens, each available in SPF30 or SPF50.

Sources :

  • ORESAJO C. & al. Evaluation and effectiveness of a photoprotection composition (sunscreen) on subjects of skin of color. Journal of the American Academy of Dermatology (2015).

  • BAD-CASINTAHAN F. & al. Frequency and characteristics of acne-related post-inflammatory hyperpigmentation. The  Journal of Dermatology (2016).

  • HAMZAVI I. H. & al. The role of sunscreen in melasma and postinflammatory hyperpigmentation. Indian Journal of Dermatology (2020).

  • MADAN R. Post-inflammatory hyperpigmentation: A review of treatment strategies. Journal of Drugs in Dermatology (2020).

  • SANGHA A. M. Managing post-inflammatory hyperpigmentation in patients with acne. Journal of Clinical and Aesthetic Dermatology (2021).

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