A hair follicle is a living tissue. A lot of things take place after the follicle is planted into the new site. Understanding of the natural histochemical process is crucial, as a better graft survival means a better outcome.
After the graft is harvested from the donor area, it is placed in a storage solution for preservation until implanted in the recipient area. Its original blood supply is detached. Oxygen is depleted and waste products begin to accumulate. The ability of the graft to receive nutrients from the recipient site and undergo revascularization (formation of new blood vessels) therefore determines survival. After the graft is inserted into one of the slits, the wound healing process immediately takes place. There is a cascade of cellular activities – edema (swelling), erythema (redness), hair shedding, new hair formation, and the revascularization of the hair graft.
Clinical Features
Swelling
Most patients would have slight to moderate edema in the transplanted area immediately after surgery. The swelling usually disappears after one week.
Redness
Erythema is present after the surgery but decreases gradually over time. In most case the redness is not noticeable after 2-4 weeks.
The Scab (Dead Skin)
It falls off after 1-2 weeks, facilitated by the use of olive oil.
Histological Changes
• On day 1, only edema is found
• By day 3, important influx of neutrophils and occasional eosinophils
• By day 7, neutrophils and macrophages are both present
• By day 14, predominant cell types seen are macrophages, fibroblasts, lymphocytes, occasional histiocytes
• From days 21 to 28, inflammatory cells decrease and then disappear
• Collagen III and IV present from day 1 to 6 months
Graft Survival
It may take 4–8 hours to complete the insertion. The elapsed time is critical for hair growth and survival because increased time results in decreased survival. As oxygen is depleted and waste products such as carbon dioxide, sugar, and urea begin to accumulate, a newly planted hair graft will be acidotic. The first 48–96 hours after implantation is critical. If the circulation cannot be re-established (the primary inosculation) to correct the metabolic imbalances, the hair graft won’t survive and could die.
Reperfusion after ischemia can also produce apoptosis and/or necrosis of the hair graft and the release of free radicals. This is called "ischaemic re-perfusion injury". The revascularization phase for a hair graft is gradual. Therefore it is critical to decrease the ischemia time and accelerate the revascularization phase. Maintaining a healthy blood supply to the scalp and minimizing hypoxia and ischemia of the hair graft during hair transplant surgery and up to a minimum of 4 to 5 days post-op should increase the survival rate.
Shedding of the Transplanted Hair
After the transplanted hair graft is taken and survives, the process may continue with one of the following scenarios:
• A small percentage of hair continues to grow from day 1 with no shedding
• Most hair will fall out after 1–6 weeks (anagen effluvium)
• Some hair will take a longer 7–12 weeks to fall out (telogen effluvium)
After the hair falls out a new hair will begin to grow 2–4 weeks later. By the 6th month most of the recipient area shows new hair growth. As hairs within a single follicular unit can have different hair cycles: some hair grew and some fell out. It is unpredictable but seems to be helped by the use of Minoxidil as adjuvant therapy.
