NOTCH signaling in the skin exerts a pivotal role in the regulation of normal keratinocytes turnover by mediating the balance between proliferation, differentiation, apoptosis and autophagic flux progression. Two skin diseases are characterized by the presence of gene variants that cause an impairment in NOTCH signaling: hidradenitis suppurativa(HS) and Dowling-Degos disease(DDD). To date, both HS and DDD are orphan diseases still lacking of specific treatments. This project aims at improving the current knowledge on the pathogenesis of HS and DDD, by deepening the understandings on the role played by keratinocytes in these pathologies and also by determining why mutations found in the same pathway cause different diseases. This study aimed to obtain in vitro models, derived directly from patients (from hair follicles) and from keratinocytes (HaCaT) cell cultures, for the study of these skin pathologies and also for the testing of novel innovative therapies such as photobiomodulation therapy.