Growth factors are present in the follicular bulge area, where stem cells are found, and they interact with cells of the matrix, thus activating the proliferative phase of the hair. Stem cells are more primitive and of ectodermal origin; they give origin to the epidermal cells and the sebaceous glands. Cells of the dermal papilla, which are found at the capillary base, are of mesenchymal origin. Both cells are reliant on each other, and thus, when they interact through the stimulation of various growth factors, they give rise to the future follicular unit. 
While some growth factors are pro inflammatory and have negative effects on hair, other growth factors such as Platelet Derived Growth Factor (PDGF) and Vascular Endothelial Growth Factor (VEGF) are important for hair formation and follicle size.
PDGF signals are involved in both epidermis-follicle interaction and the dermal mesenchyme interaction required for: hair canal formation and the growth of dermal mesenchyme. 
In 2001, McElwee was the first to perform functional assays on hair follicle growth under the influence of VEGF. This growth factor has an important role in controlling hair biology and hair follicle size is partly dependant on VEGF induced angiogenesis. 
Other studies by Yano provided the first direct evidence that VEGF improved follicle vascularisation, promoted hair growth and increased follicle and hair size and studies by Rinaldi, demonstrate that VEGF accelerated revascularization and increased the size of the follicular unit.

The use of PRP in hair restoration surgery has multiple advantages. Carlos Uebel, MD first demonstrated that the use of PRP leads to increased follicular unit yield by 15.1%, suggesting an increase of 480 hairs per every 100cm2 transplanted surface area.
Numerous studies have demonstrated the use of PRP in hair transplantation leads to diminished scalp erythema, crusting, decreased patient discomfort, swelling, accelerated hair growth and increased size of follicular units.
In 2007, Greco suggested utilization of PRP in donor sites to promote quicker healing, less scarring and infusing PRP into the recipient site to promote vascularization to the new transplanted follicles. Since PRP treated patients hair matured sooner than non transplanted patients, a study was done in 2008 to ascertain effects of PRP on non transplanted hair and it indicated increased hair diameter in the PRP treated group.

Platelet rich plasma has been utilized in hair restorations surgery since 2004 and its role is expanding as more physicians understand the benefits in this surgical procedure. While still experimental, the use of PRP in patients as an adjunct treatment to thicken hair is gaining popularity and has been used since 2007. Double randomized independent studies are ongoing to further evaluate the efficacy of its use for this purpose, but because it is autologous (same donor) it is a safe therapy.

Absolutely, because its mechanism of action is different and when used in combination with a DHT blocker, Rogaine or photo therapy it seems to have synergistic effect.

Thus far there have been positive results in both men and women. Because females have less treatment options females experience less shedding within a few weeks and an improved character to their hair sooner than males because most males having PRP done are already on other FDA approved therapies. Most patients both male and female report an improvement in hair character.
Norwood I, II, III patients, younger patients just beginning to miniaturize see best results with increase aesthetic density while Norwood IV, V patients tend to maintain hair. There are some positive results with Norwood VII patients reversing miniaturization in the fringes of the donor by three inches.
Ludwig I female patients generally increase aesthetic density while Ludwig II patients seem to maintain their hair. Almost all patients will see an improvement in the character of hair being shiner, less brittle and less shedding in time.

It is not unusual for shedding to continue or even increase when first starting a treatment for hair loss be it Rogaine, Finasteride or PRP. Hair follicles may increase in growth rate or increase diameter a little while in the growing stage, but it is not possible for hair to undergo a noticeable change in size during this stage. The reason for this is that the follicles must go into dormancy or the telogen “resting” phase so it can begin to restructure its processes to produce a thicker, stronger hair.

While the treatment is still considered experimental, improvement in hair character, decreased shedding, and increased aesthetic hair density has been seen in Androgenic Alopecia and Telogen Effluvium. There are no permanent treatments for Alopecia Areata, but PRP is being used as treatment option and demonstrated growth in some of these patients.

Results are seen within two months. Less shedding of hair has been observed in less than one month with peak effect coming at four months to 6 months.

The cost per session averages $1,000 and that will vary among geographic location and clinic.

The treatment takes about 45minutes from the time of the initial blood draw for processing to the end of the procedure. There is no down time and you may shampoo your hair the following day. Other than avoiding aspirin type products there is no follow up care.

Yes, it is and like any treatment therapy for hair once you stop the treatment your hair will revert back to where it was before treatment.

There is a bell shaped curve effect with PRP and one treatment seems to last up to 10 to12 months, however it is possible to have treatments done prior to that time without any problem.

The only pain you will experience is mild because the treatment area is numbed with local anesthesia. Your scalp can feel slightly sore the next day and Tylenol is recommended.

The beauty of the treatment is that no after care is required other than shampooing your hair the next day. It is not necessary to sleep in any particular position or refrain from any normal activity.

Most patients can fly the same day of the treatment it is not necessary to avoid physical activity or miss work.

The growth factors immediately bind to the external surface of the cell membranes of cells in the graft, flap, or wound via transmembrane receptors. The importance of this is that the PRP growth factors never enter the cell or its nucleus, they are not mutagenic, and they act through the stimulation of normal healing, just much faster. Therefore, PRP has no ability to induce tumor formation and has never done so." (Marx, RE, 2001), (Schmitz, et al, 2001)

PRP is actually bactericidal (a substance that kills bacteria). While platelets are increased in PRP processing so are leukocytes (white cells that fight infection) over 6 to 8 times. This is one reason why PRP is so effective in wound healing. Not only do the increased levels of leukocytes enable the body to fight off infection they have a duel purpose. After platelets initially release their growth factors, leukocytes produce a secondary release or growth factors to promote healing.