Nikolsky's sign is a clinical dermatological sign, named after Pyotr Nikolsky (1858–1940), a Russian physician who trained and worked in Ukraine, which was part of the Russian Empire at that time. The sign is present when slight rubbing of the skin results in exfoliation of the outermost layer.
Nikolsky's sign is almost always present in toxic epidermal necrolysis and is associated with pemphigus vulgaris. It is useful in differentiating between pemphigus vulgaris or mucous membrane pemphigoid (where it is present) and bullous pemphigoid (where it is absent). The Nikolsky sign is dislodgement of intact superficial epidermis by a shearing force, indicating a plane of cleavage in the skin. Also present in Staphylococcal scalded skin syndrome caused by the exfoliative toxin of Staphylococcus aureus.