Damage and necrosis of hair follicles after scalp trauma are actually the result of the body’s own natural defense mechanisms:
Hematoma- A possible cause of very early post-trauma hair loss (seconds to minutes)
After a blunt or sharp trauma the skin begins to bleed in two places : The first and most distressing is OUTSIDE the skin. The second is inside and under the skin. The skin of the scalp contains several layers. The most important are, from the outside inward: epidermis, dermis, and fat.
- The epidermis is very thin and easily disrupted. It’s main job is to keep moisture in so we don’t dry out.
- The dermis is where most of the “action” related to skin happens. It is in this dense layer that the organelles of the skin mostly live such as sweat glands and hair follicles.
- And then there is the fat layer. This level acts as a cushion or shock absorber but because it is fluffy and low in density it is the perfect place for ruptured blood vessels to actively bleed into and pool.
As the blood naturally coagulates a lump begins to form which can expand to excruciating levels. In doing so, just the high pressure associated with this expansion may be all that is needed to kill some hair follicles- either through direct trauma or through the strangling of the blood supply. If a hematoma isn’t drained surgically, or doesn’t drain on its own naturally, calcium can begin to form within the clot before it is absorbed leaving a permanent lump that literally feels like bone.
Edema- A possible cause of early post-trauma hair loss (hours to days)
This is the swelling that begins almost immediately after the trauma. This is a normal defense mechanism used by the body and is effective in slowing blood loss in the case of scalp rupture secondary to blunt or sharp trauma. By “puffing” the skin up it allows the scalp to cushion another traumatic blow should it come, thereby distributing the force (or heat) of the trauma over a much larger area. It’s like the body makes a small temporary pillow appear over the wounded area.
Say for example: the swelling was caused by being hit on the head during a mugging. The first strike would rupture the skin and allow a lot of energy to reach the skull. But if another strike comes later, the engorged scalp skin can act as a shock-absorber. It is a miraculous mechanism of the body but the price may well be the hair follicles. The edema itself can be of such high pressure that it might kill weaker hair roots almost immediately. But more likely it is the decreased perfusion of blood through the edema that is the likely cause of most follicular death right after scalp swelling. Follicles, like everything else living, rely on blood vessels to survive. Swelling edema may actually strangle these tiny blood vessels just long enough to prevent perfusion of the distant tissue thus causing cell death. Ultimately the edema will drain, and if the blood vessels themselves weren’t damaged they will re-open allowing blood to flow again. Follicles that could survive the diminished blood flow may well wake up and grow just fine. But they may also only grow in at a fraction of their normal caliber. And, of course, some will never regrow again leaving a bald patch.
Fibrosis-A possible cause of late post-trauma hair loss (weeks to months)
This is another normal defense mechanism of the body and can be viewed as the “end game” after trauma. Once the initial trauma is over and the edema drains away- the scalp skin begins to make the injured areas physically tougher. Imagine the seam on any clothing. The fabric is always soft and flexible to the touch until you reach the seams where it becomes obviously more stiff and rough. This is because the uniform flow of the fibers has been disrupted. The same thing for the scalp in the case of fibrosis.
The major problem with fibrosis is that it limits the amount of blood vessels that can grow through it. So if there are hair follicles in the vicinity of significant fibrosis as it develops they may become injured or die. This may result in a complete loss of hair, patchy loss, or just a marked thinning of the hair shaft itself. Just look at the man in the photo to your left. That entire area is fibrotic with almost no hair growth.
A real world example of this effect is after the sharp trauma inflicted by all Follicular Unit Extraction (FUE) procedures. Every time an attempt is made to remove individual grafts from the back of the head the hole left by the tiny punch heals in by fibrosis. The surgical term for this is “secondary intention”, but in reality is just means: “allowing the skin to close itself by scarring.”
Scarring is fibrosis. And Fibrosis is scarring.
During the FUE procedure the holes left behind in the donor area are very small, however, there are so many of them that the cumulative effect of fibrosis is massive- about ten times that of an equivalent sized Follicular Unit Transplant (FUT) procedure. The end result is noticeable thinning throughout the donor area giving a see-through and unnatural appearance. It also decreased the number of grafts that can be obtained for future Hair Transplant Procedures should they be needed.
This problem is becoming more apparent as more and more FUE-machine clinics pop up around the world. This is why we do not advocate for large FUE sessions and try to direct patients who need to cover large areas of thinning and balding more toward the FUT(Strip) procedure.
The Good Fibrosis– Not all fibrosis is bad, however. In fact it is actually needed for a successful Hair Transplant. When grafts are inserted into the tiny slits within the balding and thinning areas we actually rely on fibrosis to lock the graft down permanently. The fibrotic attachment is so strong that if the hair pulled the surround skin will rip free before the graft is pulled out. Think of concrete. See the photos below. These are close ups of a newly created hairline and frontal scalp area. Every hair you see standing is “new”. That is, they came from the donor area in the back. This hair will take root by fibrosing to the surrounding dermis and then go into a sleeping mode. About 4 months later the hairs will wake up producing new hair that when grown longer with the other transplanted hairs should look quite pleasing.