Post-inflammatory hyperpigmentation: definition and causes.

Sometimes referred to as hyperpigmented scars, these marks are a type of hyperpigmentation. They present themselves in the form of persistent flat brown or black spots (see photo above), depending on the skin colour.

As their name suggests, they appear following a skin inflammatory response, which can be triggered by an acne outbreak, atopic dermatitis, psoriasis, certain aesthetic treatments (dermabrasion, chemical peeling and laser treatment) or even an injury.

They are caused by a heightened production of melanin in response to the inflammatory reaction in question. Indeed, the emergence of these hyperpigmented areas is based on the production of inflammatory cytokines, which have pro-pigmenting properties, by the surrounding cells. They will activate the melanocytes (cells that produce melanin), leading to a significant release of melanosomes (pigment granules) and thus an excess of melanin.

Although this phenomenon can affect all skin types, it is generally more common in individuals with mixed to dark skin (phototypes IV to VI). Indeed, these subjects contain more melanin and their melanosomes are more reactive. Furthermore, a study conducted in 2016 specifies that post-inflammatory hyperpigmentation marks resulting from acne flare-ups take time to fade, at least 1 year for more than half of the subjects surveyed and this can go up to 5 years for some. The majority of patients also reported that this hyperpigmentation is as bothersome, if not more bothersome, than the acne itself.

When the skin barrier is damaged by any form of inflammation (acne, injury, diseases...), the healing area becomes a part of the skin where it is thinner and more fragile. Therefore, it is particularly vulnerable to the sun's UV rays. If you expose the irritated area to the sun, the skin will overreact to protect itself and recruit a significant amount of pro-inflammatory molecules such as cytokines. The result: an excessive and localised production of melanin which will further contribute to the appearance of a post-inflammatory hyperpigmentation spot.

Furthermore, a 2015 study demonstrated that effective sun protection could mitigate the appearance of post-inflammatory hyperpigmentation marks. Participants were randomly assigned to receive either an SPF30 or SPF60 sunscreen, applied daily for 8 weeks during the summer. The results showed a lightening of pre-existing hyperpigmented spots in 81% of patients and a decrease in the number of spots in 59% of patients. Moreover, those who used the SPF60 sunscreen showed greater improvements in the overall lightening of brown spots compared to patients using the SPF30 sunscreen. However, it should be noted that the lack of a control group is a limiting factor in this study.

In all instances, ensure you protect yourself daily from the sun by applying abroad-spectrum SPF sunscreenand limit your exposure as much as possible. To shield yourself from the sun's UV rays, choose one of our body or face sunscreens, each available in either a SPF30or aSPF50.

• ORESAJO C. & al. Assessment and efficacy of a photoprotection formulation (sunscreen) on individuals with skin of colour. 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. & co. The role of sunscreen in melasma and post-inflammatory 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).