The present invention relates to methods and compositions for inhibiting the activity of skin proteases, especially human kallikrein 7 (KLK7), human kallikrein 5 (KLK5), and human kallikrein 14 (KLK14). More specifically, the invention relates to the use of substituted 3,1-benzoxazin-4-ones being selective inhibitors of human skin kallikreins for the treatment of skin diseases, more specifically for the treatment of inflammatory skins diseases, especially Netherton syndrome.