Acquired Blaschko dermatitis (ABD; also known as blaschkitis, adult blaschkitis, or acquired relapsing self-healing Blaschko dermatitis) is a rare dermatologic disorder characterized by linear bands of papules or papulovesicles along Blaschko lines. These lines are thought to represent the embryologic migration of ectoderm, forming a V-shape over the spine, an arc or S-shape across the anterior and lateral torso, and straight lines down the upper and lower extremities. The etiology of the disease is thought to involve a T-cell mediated autoimmune reaction against genetically distinct keratinocytes in the context of genetic mosaicism.

The classic presentation of ABD involves a rapid onset of 1-4 mm pruritic, erythematous, edematous papules or papulovesicles that coalesce to form plaques across single or multiple lines of Blaschko. The bands are typically 2-4 cm wide, and when unilateral, there is a strict demarcation at the midline. Papules may have a fine scale. ABD typically resolves in weeks to months without treatment, though multiple recurrences may occur over the following months and years. The trunk is affected most frequently followed by the extremities, with rare involvement of the neck and face. The disease is typically seen among men and women in their fourth to fifth decade of life.

The classification of ABD has been controversial in the literature. Some authors classify it as the adult form of lichen striatus. Others view it as a separate diagnosis given its distinctive histopathology as well as the fact that typical lichen striatus cases are encountered in adults.