Lichen planus is a chronic inflammatory disease of unknown origin, which most commonly affects individuals between 30–60 years of age and is characterized by different types of lesions involving the skin and mucosa. The most common lesions are purple papules with well-demarcated, irregular borders, which typically occur on the wrists, lower extremities, and genitoanal region. The surfaces of the lesions often exhibit a pattern of white lines known as Wickham's striae. The disease is diagnosed clinically, but may be confirmed through dermoscopy and punch biopsies. Biopsy also helps detect squamous cell carcinoma, the risk of which is increased in lichen planus. Treatment primarily consists of high-dose topical steroids but may also include oral steroids and phototherapy in cases of extensive or steroid-refractory disease. Lichen planus is generally a chronic-recurrent condition, except for the cutaneous form, which is usually self-limiting.
Cutaneous lichen planus 
May occur simultaneously with other subtypes
- Distribution pattern
Mucosal lichen planus
- Oral lichen planus
- Esophageal lichen planus
Genital lichen planus
The 6 P's of lichen Planus are: Pruritic, Polygonal, Planar (flat-topped), Purple Papules, and Plaques.
Subtypes and variants
Lichen planus can manifest with several subtypes, including: 
- Hypertrophic lichen planus (lichen planus verrucosus)
- Mainly affects the scalp of postmenopausal women and presents with pruritus and hair loss
- Frontal fibrosing alopecia (a variant of lichen planopilaris)
Lichen planus is clinically diagnosed based on the presence of typical skin lesions. Additional testing is performed to confirm the diagnosis and rule out other diseases.
- Lichen sclerosus
Drug-induced lichen planus (lichenoid drug eruption)
- A dermatologic condition that is triggered by certain drugs (e.g., beta blockers, ACE inhibitors, penicillamines, thiazide diuretics, hydroxychloroquine)
- Manifests with diffuse lesions that closely resemble lichen planus but are not histologically identical. 
- Management includes discontinuation of the suspected medication and topical glucocorticoids.
- guttate psoriasis and plaque psoriasis) (
The differential diagnoses listed here are not exhaustive.
- First-line therapy
- Second-line therapy
- Adjunctive therapy: oral antihistamines (e.g., hydroxyzine) to manage pruritus 
Any localization of erosive lichen planus can cause scarring, which may lead to functional limitations.