Lichen planus pigmentosus (LPP, not to be confused with lichen planopilaris) is a rare variant of lichen planus (LP). Classically, it presents as patchy brown or gray pigmentation in sun-exposed areas. Rare variant presentations include lichen planus pigmentosus inversus (LPP-inversus) and LPP along Blaschko lines (linear LPP). Although LPP most often exists in isolation, it occurs with other forms of LP in around 20% of cases, including frontal fibrosing alopecia (FFA), lichen planopilaris, oral LP, and classic LP.

LPP is most common in people with intermediate and darker skin colors, is rare in people with lighter skin colors, and has a slightly higher prevalence in women than men. The condition most commonly occurs between the third and fifth decades of life. The time course of LPP is unpredictable, ranging from 6 months to 3 years. The condition is most often described as chronic and progressive with periods of remission and exacerbation. Lesions are usually asymptomatic but can be mildly itchy in some patients.

In LPP, CD8+ autoreactive T cells attack epidermal keratinocytes, leading to an inflammatory lichenoid response. The initial inflammatory infiltrate resolves relatively quickly and leaves behind marked dermal pigmentary incontinence.

LPP has been shown to be more prevalent in patients with hepatitis C virus, diabetes, thyroid disease, and dyslipidemia. Furthermore, 2 Indian studies have linked LPP to the use of mustard oil, amla oil, henna, hair dye, and nickel. Hormonal factors also may play a role as LPP often presents in women around menopause. LPP has also been shown to be triggered by surgery and by COVID-19 vaccination.