Hair transplantation
Hair transplantation involves relocating (transplanting) bald resistant hair follicles from the back and sides of the head (the donor areas) to a persons bald or thinning areas. The transplanted hair follicles will typically grow hair for a lifetime because they are genetically resistant to going bald. In recent years hair transplantation techniques have evolved from using large plugs and mini grafts to exclusively using large numbers of small grafts that contain from between 1 to 4 hairs.
Since hair naturally grows in follicles that contain groupings of 1 to 4 hairs, todays most advanced techniques transplant these naturally occurring 1  4 hair "follicular units" in their natural groupings. Thus modern hair transplantation can achieve a natural appearance by mimicking nature hair for hair. This recent hair transplant procedure is called "Follicular Unit Transplantation." 
Given the improved naturalness of hair transplantation surgery hair loss sufferers are increasingly selecting this hair loss treatment.

# History
The use of both scalp flaps, in which a band of tissue with its original blood supply is shifted to the bald area, and free grafts dates back to the 19th century. Modern transplant techniques began in Japan in the 1930s, where surgeons used small grafts, and even "follicular unit grafts" to replace damaged areas of eyebrows or lashes. They did not attempt to treat baldness per se. Their efforts did not receive worldwide attention at the time, and the traumas of World War II kept their advances isolated for another two decades.
The modern era of hair transplantation in the western world was ushered in the late 1950s, when New York dermatologist Norman Orentreich began to experiment with free donor grafts to balding areas in patients with male pattern baldness. Previously it had been thought that transplanted hair would thrive no more than the original hair at the "recipient" site. Dr. Orentreich demonstrated that such grafts were "donor dominant", as the new hairs grew and lasted just as they would have at their original home.  Today Dr. Orentreich's practice still performs hair transplants.
For the next twenty years, surgeons worked on transplanting smaller grafts, but results were only minimally successful, with 2-4 mm "plugs" leading to a doll's head-like appearance. In the 1980s, Uebel in Brazil popularized using large numbers of small grafts, while in the United States Rassman began using thousands of micrografts in a single session.
In the late 1980's, Limmer introduced the use of the stereo-microscope to dissect a single donor strip into small micrografts.  In 1995, Bernstein and Rassman published the first paper on "Follicular Unit Transplantation." where hair is transplanted exclusively in naturally occurring groups of 1-4 hairs.  With microscopic dissection of donor pieces from an excised portion of scalp, individual follicular units containing but 1-4 hairs could be prepared and individually relocated into needle punctures in the recipient areas. Since the transplanted hair mimics the way hair grows in nature, completely natural results were attainable.
The follicular unit hair transplant procedure has continued to evolve, becoming more refined and minimally invasive as the size of the graft incisions have become smaller. These smaller and less invasive incisions enable surgeons to place a larger number of follicular unit grafts into a given area. With current techniques, over 50 grafts can be placed per square centimeter, when appropriate for the patient.
Surgeons have also devoted more attention to the angle and orientation of the transplanted grafts. The adoption of the lateral slit technique in the early 2000s, enabled hair transplant surgeons to orient 2 to 4 hair follicular unit grafts so that they splay out across the scalp's surface . This enabled the transplanted hair to lie better on the scalp and provide better coverage to the bald areas.

## The procedure
At an initial consultation, the surgeon analyzes the patient's scalp, discusses his preferences and expectations, and advises him/her on the best approach (e.g.,single vs. multiple sessions) and what results might reasonably be expected.
For several days prior to surgery the patient refrains from using any medicines, or alcohol, which might result in intraoperative bleeding and resultant poor "take" of the grafts. Pre-operative antibiotics are commonly prescribed to prevent wound or graft infections.

## Cost
In recent years hair transplants have become less expensive. Prices typically range from $3.00 to $7.00 per graft, with $4 to $5 per graft being about average. Normally the price per graft also drops as the size of the surgical session increases. Depending on the needs of the patient a typical surgical session can range from 1,500 to over 4,000 grafts, resulting in a total cost of approximately $6000 to $15,000. A few clinics offer larger sessions of up to 6000 grafts in one sitting.

## Surgery
Transplant operations are performed on an outpatient basis, with mild sedation (optional) and injected topical anesthesia, and typically last about four hours. The scalp is shampooed and then treated with an antibacterial chemical prior to the donor scalp being harvested.
In the usual follicular unit procedure, the surgeon harvests a strip of skin from the posterior scalp, in an area of good hair growth. The excised strip is about 1-1.5 x 15-30 cm in size. While he is closing the resulting wound,  assistants begin to dissect individual follicular unit grafts from the strip. Working with binocular microscopes, they carefully remove excess fibrous and fatty tissue while trying to avoid damage to the follicular cells that will be used for grafting.
The surgeon then uses a fine needle to puncture the sites for receiving the grafts, placing them in a predetermined density and pattern, and angling the wounds in a consistent fashion to promote a realistic hair pattern. The assistants generally do the final part of the procedure, inserting the individual grafts in place.

## Post-operative care
Advances in wound care allow for semi-permeable dressings, which allow seepage of blood and tissue fluid, to be applied and changed at least daily. The vulnerable recipient area must be shielded from the sun, and shampooing is started two days after the surgery.  Some surgeons will have you shampoo the day after surgery. Shampooing is important to prevent scabs from occurring around the hair shaft.  Scabs adhere to the hair shaft and increase the risk of loosing newly transplanted hair follicles during the first 7 to 10 days post-op.
During the first ten days, virtually all of the transplanted hairs, inevitably traumatized by their relocation, will fall out ("shock loss"). After two to three months new hair will begin to erupt from the moved follicles. The patient's hair will grow normally, and continue to thicken through the next six to nine months. Any subsequent hair loss is likely to be only from untreated areas. Some patients elect to use medications to retard such loss, while others plan a subsequent transplant procedure to deal with this eventuality.

# Side effects
Hair thinning,  known as "shock loss", is a common side effect that is usually temporary. Bald patches are also common, as fifty to a hundred hairs can be lost each day.
Other side effects include swelling of areas such as the scalp and forehead. If this becomes uncomfortable, medication may ease the swelling. Additionally, the patient must be careful if his scalp starts itching, as scratching will make it worse and cause scabs to form. A moisturizer or massage shampoo may be used in order to relieve the itching.