The Koebner phenomenon refers to a skin condition in which the erythematous plaques of plaque psoriasis develop in response to trauma such as burns, friction, sunburn, contact dermatitis, chemical irritation or tattooing.  This condition is associated with psoriasis, lichen planus, vitiligo, and other cutaneous disorders.  Certain medications to include lithium, antimalarials, beta blockers, calcium channel blockers, ACE inhibitors, and interferon may cause an endogenous Koebner phenomenon in which patients may develop psoriasis or suffer worsening of their underlying psoriatic disease while on these medications.