Adult stem cells refer to undifferentiated cells existing in differentiated human tissues. Their differentiation potential is weaker than embryonic stem cells. Those cells can self-renewal and differentiate into cells in their corresponding tissue. Its physiological significance is for renewing aging/dead cells during normal aging processes and maintaining the normal function and structure of human tissue. Adult stem cells are regarded as the “reserved force” of the body. Adult stem cells reside in all types of tissues and organs in the human body, current discovered adult stem cells include hematopoietic stem cells, bone marrow stromal cells, neural stem cells, liver stem cells, skin stem cells, intestinal stem cells, retinal stem cells, pancreatic stem cells, etc.