Nevocellular nevus can develop by two mechanisms: 1. after the chronic solar irradiation of the skin which impairs barrier lipids' homeostais and keratinocytes together with melanocytes undergo apoptosis; 2. Apoptosis can arise in melanocytes during phylogenetic development from the neural crest to epidermis when it migrates through the "enemy" territory of dermis. Apoptosis can be thus stopped by enzymatic process which results in anoikis and the endangered melanocyte would further proliferate. The later is the path of nevocellular nevi.