Lichen planus (LP) is a pruritic papulosquamous eruption in which autoreactive T lymphocytes attack basal keratinocytes in the skin, mucous membranes, hair follicles, and/or nail units. The etiology is unclear, but viruses, medications, or contact allergens have all been implicated.

Childhood LP has been described after hepatitis B vaccination. Drugs causing LP-like eruptions (lichenoid drug reactions) include antihypertensives (ACE inhibitors: captopril and enalapril; beta blockers: propranolol and labetalol), thiazide diuretics, antimalarials (quinidine and hydroxychloroquine), penicillamine, NSAIDs, griseofulvin, tetracycline, antiepileptics, and many other drugs.

LP usually affects the glabrous (non-hair-bearing) skin and sometimes the mucosa, scalp, and nails. (See oral lichen planus for oral mucosal presentation and see lichen planopilaris for scalp presentation.) The frequency of childhood LP varies from 2.1%-11.2% of all cases of LP.

The majority of children who develop LP develop the classic form. Other variants include actinic, hypertrophic, linear, eruptive, follicular, atrophic, and bullous lesions.

LP may resolve spontaneously over several months. However, the disease generally has a chronic course with frequent remissions and exacerbations.