(8)Micro-revolution in Embryology of Cutaneous Adnexae

Abstract

The development of all skin appendages (hair follicles, sebaceous glands, sweat glands, nails) has been embryologically considered to be“down-growth from skin ectoderm”(down-growth theory). This may be true from the viewpoint of the xed position of the epidermis. However, it is possible to change the viewpoint and think that“the skin thickens while leaving the deepest part of each adnexa xed”(stay-in theory). Are these two ways of thinking merely“relative differences”that “look at one phenomenon from a different way”? These two perspectives were compared for following 10 items : consistency of direction, waste of energy, destruction of dermis, movement with the mesenchymal cell mass, relationship between cellular differentiation and proliferation, development of apocrine glands, development of sebaceous glands, development of arrector pili muscles, formation of perifollicular sheath, and the interface between dermis and subcutaneous adipose tissue. As a result, it seems that the“stay-in theory”can explain these 10 items better. Although it is not a concerning problem for daily medical practice, it may be not useless for dermatologists to consider the embryological development of skin appendages. Skin Research, 18 : 59-70, 2019