Post-inflammatory hyperpigmentation (PIH) is an acquired pigmentary disorder that results from a preceding inflammatory skin disorder, injury, or similar cause (Callender, St Surin-Lord, Davis, & Maclin, 2011). PIH is more common in darker-skinned individuals of Fitzpatrick skin phototypes III-VI than in individuals with lighter skin (Davis & Callender, 2010) and frequently occurs in east Asians. The causes of PIH are various, including inflammatory conditions, such as atopic dermatitis, contact dermatitis, and psoriasis, infections, treatments such as laser irradiation and chemical peeling, sunburn, injury, and other forms of skin damage (Silpa-Archa, Kohli, Chaowattanapanit, Lim, & Hamzavi, 2017). Among those causes, PIH after atopic dermatitis often covers wide areas of skin and can be a significant concern for many patients. PIH also causes cosmetic issues that markedly diminish the quality of life (QOL) and restrict social activities (Seghers et al., 2014). However, the pathophysiology of PIH remains poorly understood, one reason being that an appropriate animal model for research has not been established.