Is this common? Why is this?
Psoriasis very often appears where skin has previously been injured. This phenomenon is called the Koebner phenomenon. It is named after its discoverer, Dr. Heinrich Koebner, a dermatologist in Germany who first described the phenomenon in 1872. The appearance of psoriasis after trauma is often called Koebner-ization and usually appears between 2 and 6 weeks after trauma to the skin. This phenomenon is found in some people with psoriasis, as well as those with other skin diseases like vitiligo and warts.
Koebnerization is thought to occur through the normal inflammation in traumatized skin. When skin is injured, a normal inflammatory reaction occurs with redness, warmth, pain, and swelling. In normal skin this inflammation resolves after the skin damage is healed. In contrast, the inflammatory reaction in a pso-riatic patient attracts the skin-reactive immune cells in addition to the normal response. These cells don’t simply aid in skin repair, but create changes in psoriasis in the traumatized area.
One reason that psoriasis is thought to be common on the elbows and knees is that these locations are constantly exposed to the slight trauma of stretching at flexible joints and rubbing against hard surfaces, which may cause ongoing Koebnerization at these sites.
Because of the Koebner phenomenon, traumatic skin procedures should be avoided whenever possible. Tattoos, including permanent makeup, can cause trauma that leads to Koebnerization. Skin-resurfacing techniques such as dermabrasion, often used for acne scars and skin tightening, could cause Koebnerization and psoriatic changes in previously healthy facial skin.
When trauma does occur, protect the skin as much as possible with occlusive bandages such as Band-Aids or other wound dressings. Keep injured skin greasy with ointments such as Aquaphor or Vaseline, or antibiotic ointments such as bacitracin, mupirocin (Bactroban), neomycin (Neosporin), or polymyxin (in Polysporin). Contrary to popular belief it is not necessary for a scab to form in order for the skin to heal.
In fact, the presence of a hard scab can block the skin from covering an injured area. Avoid drying out injured areas since dryness can cause skin tightness, scab formation, and rebreaking of the skin. Strong antiseptics like hydrogen peroxide or rubbing alcohol are rarely needed. Diligent care for skin injuries can minimize or prevent Koebnerization of psoriasis to injured skin.
The potential for Koebnerization varies among people, and not every person will have problems with psoriasis appearing after trauma. For unknown reasons, this phenomenon can come and go over a lifetime.