Stem cells in the skin generate cells that can differentiate themselves into surface tissue or hair follicles, as explained by ScienceDaily, and this process occurs roughly every 27 days. The skin, which is the largest organ in the body, is an outer covering of dead cells and four epidermal layers. WebMD explains that the epidermis hosts different types of cells, including keratinocytes, which produce keratin, the major component of skin.
Rockefeller University researchers discovered two proteins, TCF3 and TCF4, that are necessary for epidermal stem cell regeneration, according to a 2009 article in ScienceDaily. Additionally, EuroStemCell explains that scientists have identified epidermal, hair follicle and melanocyte stem cells. Hair follicle stem cells can regenerate damaged epidermis and sebaceous gland tissues as well as hair follicles. Melanocyte stem cells regenerate cells that make the melanin pigment in skin. Epidermal stem cells can be used to grow sheets of epidermis in a laboratory, which is then grafted back onto the donor, but EuroStemCell explains that the transplanted skin contains only epidermal cells and lacks hair follicles and sweat glands. Tissue regeneration can be impaired by chronic diseases such as diabetes, according to the Max Planck Institute for Biology for Ageing, which in turn can delay wound healing and increase mortality.