Q: I’ve heard a lot about platelet-rich plasma (PRP). What is platelet-rich plasma, and how does it promote hair growth? — A.V., Scarsdale, NY
A: To begin, first let’s define a few basic terms: blood plasma, platelets and PRP
What Is Blood Plasma?
Blood plasma holds the blood cells in a liquid suspension. Blood plasma makes up about 55% of the body’s total blood volume. There are three basic types of blood cells: red blood cells (that carry oxygen), white blood cells (that have immune functions to help fight infection) and platelets (that facilitate coagulation, wound healing and repair).
What is a Platelet?
A platelet is a type of white blood cell containing approximately 50 to 80 tiny encapsulated structures called alpha-granules. Each alpha-granule contains a high number of growth factors, many playing a fundamental role in healing following tissue damage. ((Eppley BL, Pietrzak WS, and Blanton M. Platelet-Rich Plasma: A Review of Biology and Applications in Plastic Surgery. Plastic and Reconstructive Surgery, 2006.)) Many of these platelets are also known to regulate the growth cycle of hair follicles. ((Itami S, Kurata S, Takayasu S. Androgen induction of follicular epithelial cell growth is mediated via insulin-like growth factor-I from dermal papilla cells. Biochem Biophys Res Commun. 1995; 212: 988–94.))
Platelets are formed in the bone marrow and circulate throughout the bloodstream in a concentration of approximately 140,000 to 400,000 platelets/mm3.
What is Platelet-Rich Plasma?
Derived from a patient’s own blood plasma, platelet rich plasma is concentrated blood plasma which contains approximately five times the number of platelets and growth factors normally found in the blood.
How Does Platelet-Rich Plasma Work to Promote New Hair Growth?
Studies that have looked at the therapeutic effects of PRP on hair loss have found that it promotes hair survival and hair growth in both laboratory studies ((Li ZJ, Choi HI, Choi DK et al. Autologous platelet-rich plasma: a potential therapeutic tool for promoting hair growth. Dermatol Surg 2012; 38: 1040–6.)) and human clinical trials, but exactly how PRP promotes new hair growth isn’t clear. Researchers have suggested a few possible mechanisms.
In a recent pilot study ((Schiavone G, Raskovic D, Greco J, Abeni D. Platelet-rich plasma for androgenetic alopecia: a pilot study. Dermatol Surg. 2014; 40(9): 1010-9.)) that found that PRP injections resulted in noticeable improvement in both males and females with androgenetic alopecia, researchers suggested that PRP may have stimulated hair growth by prolonging the anagen (growth) phase of the hair follicle.
In another study ((Cervelli V, Garcovich S, Bielli A, Cervelli G, Curcio BC, Scioli MG, Orlandi A and Gentile P. The effect of autologous activated platelet rich plasma (AA-PRP) injection on pattern hair loss: clinical and histomorphometric evaluation. BioMed Research International 2014; 1-9)) that showed PRP promoted hair growth in males with alopecia, researchers suggested that PRP may have protected the hair follicles against one of the possible main mechanisms of pattern hair loss: the death of dermal papilla cells in the hair follicle. ((Whiting DA. Possible mechanisms of miniaturization during androgenetic alopecia or pattern hair loss. J Am Acad Dermatol. 2001 Sep;45(3 Suppl):S81-6.)) The death of these cells leads to a gradual shrinking and eventual disappearance of the hair shaft, a process called miniaturization.
Other studies have observed that PRP seems to promote the growth of new blood vessels around treated hair follicles. Because of this, researchers have suggested that the growth of new blood vessels may be helping to stimulate new hair growth. ((L. Mecklenburg, D. J. Tobin, S.Muller-Rover, et al. “Active hair growth, anagen, is associated with angiogenesis.” Journal of Investigative Dermatology 2000, 114:5; 909–916.))
In sum, while published studies so far suggest that PRP therapy is a safe and effective treatment option for male and female androgenetic alopecia, there is still a need for more extensive studies to better understand the mechanism by which PRP treatments promote hair growth.
Posted by Robert M. Bernstein M.D. 
