## 1 Introduction  
The placenta is arguably the least understood organ, perhaps due to its transitional nature [1, 2]. Despite its short lifespan, lasting 9 months of pregnancy, it performs functions typically carried out by various organs, including the lungs, liver, intestines, kidneys, and endocrine glands [3, 4, 5]. The variety of morphological forms of the placenta throughout mammals makes it hard to define by a list of common features [6]. [PERSON] stated that \"the normal mammalian placenta is the apposition or fusion of the fetal membranes with the uterine mucosa for physiological exchange\" [7]. The medicinal uses of the placenta date as far back as 2500 years ago. It has been used as an elixir of eternal youth and longevity, and is also valued as a remedy for physical and mental fatigue and weakness [8]. Traditional Chinese medicine experts believed that the placenta contains a \"life force\" and used it for boosting lactation, blood circulation, and immunity, as well as for lethargy, skin aging and hair loss [9]. [PERSON] (1885-1956) believed that any tissue of human or animal origin could be used to therapeutic purposes, even if histologically different from the diseased tissue--a concept he called the \"therapeutic tissue principle\" [10]. Althoughplacental extracts have been popular for over a century in Europe and parts of Asia (mainly China, Korea and Japan), there was no scientific evidence of their effectiveness until recently [10]. Nowadays, the placenta is known to be rich in bioactive molecules used as regenerative and anti-aging agents with significant therapeutic properties [11; 12; 13]. The composition of placenta extracts, and thus their biological effects depend on the method of preparation [14]. The manufacture of biological products for direct use in humans requires full compliance with the Good Manufacturing Practice (GMP), at all stages of production, starting from the retrieval of the raw material of which the active ingredients are made [15]. This review focuses on the use of two forms of placenta derivatives, namely placental proteins and protein hydrolysates. Placental protein extract is a mixture of proteins derived from animal placentae, whereas hydrolyzed placental proteins are produced by digesting placental proteins with acidic, enzymatic, or other hydrolysis methods (Table 1). The strongest biostimulating effects are ascribed to aqueous extracts of fresh, full-term human placenta [19]. The human placenta fulfills a variety of functions, therefore, it contains a range of biologically active compounds, most of which are proteins that act as hormones, enzymes, proenzymes, activators, inhibitors, immunoregulatory factors, transport and storage proteins, receptors or structural proteins [20]. Examples of placental-specific hormones are human chorionic gonadotropin (hCG) and human placental lactogen (hPL), placental enzymes include heat-stable alkaline phosphatase (HSAP), diamine oxidase (DAO) and oxytocinases, e.g., insulin-regulated aminopeptidase (IRAP) or leucyl and cystinyl aminopeptidase (LNPEP) [20]. Placenta extracts contain abundant amounts of vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), transforming growth factor-\(\beta\) (TGF-\(\beta\)), insulin-like growth factors (IGF), and adrenocortic hormone (ACTH) [21]. VEGF and IGF-1 from the umbilical cord protein extract can accelerate the proliferation of hair follicle (HF) and interfollicular cells [19]. The nutritional value of the human placenta is due to its abundance of proteins, including the iron storage protein ferritin and structural proteins such as collagen, fibronectin, and laminin, as well as amino