Lichen planus produces small, flat-topped bumps with a distinctive purplish color and a shiny surface. These bumps, typically 2 to 4 millimeters wide, most often appear on the inner wrists, forearms, shins, and lower back, but the condition can also affect the mouth, nails, scalp, and genitals. Each location produces a somewhat different appearance, which is why lichen planus can be tricky to recognize at first glance.
The Classic Skin Rash
Dermatologists traditionally describe lichen planus using a set of key features: the bumps are purple, polygonal (angular rather than round), flat-topped, and intensely itchy. Up close, the surface of each bump has a waxy or shiny quality. The single most telling visual feature is a network of fine white lines crossing the surface of the bumps, called Wickham striae. These lines form a lacy or fern-like pattern and are sometimes easier to see if you apply a drop of oil to the skin and look under good lighting.
The bumps often cluster together into patches or plaques. New bumps can appear in a straight line along a scratch or area of minor skin trauma, a response known as the Koebner phenomenon. So if you’ve scratched your forearm and a line of purple bumps developed in that exact spot a week or two later, that pattern is characteristic of lichen planus.
How It Looks on Different Skin Tones
On lighter skin, the bumps tend to be a faint purple with visible, interlaced white scale on top. On darker skin, the same bumps can look much deeper in color, ranging from dark purple to brown or nearly black, and the overlying scale may be hard to spot. The Wickham striae are still present but often require a closer look to see. Because the color can appear so dark, lichen planus in deeper skin tones is sometimes confused with other conditions like discoid lupus.
The discoloration left behind after the bumps heal is also more prominent in darker skin. This post-inflammatory hyperpigmentation can persist for months, sometimes longer, and often causes more cosmetic concern than the original rash. Sun-exposed areas tend to hold onto this discoloration the longest, and it can be difficult to resolve even with treatment.
Lichen Planus in the Mouth
Oral lichen planus affects the inside of the cheeks most commonly, though it can also involve the tongue and gums. It takes two main forms that look quite different from each other.
The reticular form is the more common pattern. It appears as a lacy web of slightly raised white threads on the inner cheeks, similar to the Wickham striae seen on skin lesions. Many people with this form have no pain at all and only notice it during a dental exam.
The erosive form is more troublesome. It produces bright red, raw-looking patches where the top layer of the lining tissue has worn away. This form can affect any surface inside the mouth and often causes a burning sensation, especially when eating spicy or acidic foods. Some people have both patterns at the same time, with white lacy streaks bordering areas of red erosion.
Nail Changes
When lichen planus targets the nails, the changes can range from subtle to severe. Early signs include lengthwise ridges running from the base of the nail to the tip, along with general thinning of the nail plate. As it progresses, nails may split at the free edge, become rough and brittle, or lift away from the nail bed.
The most distinctive nail finding is something called pterygium, where a wing-shaped fold of skin from the cuticle grows forward and fuses to the nail plate, creating a permanent groove or splitting the nail down the middle. Multiple fingernails and toenails can be affected at once. Unlike some other causes of nail damage, lichen planus can cause scarring that permanently alters the nail if not treated early.
Scalp Involvement
On the scalp, lichen planus goes by the name lichen planopilaris. It targets hair follicles rather than flat skin, producing red, scaly patches and rough bumps around the base of hairs. The affected areas often feel tender or itchy. Over time, the inflammation destroys the hair follicles and replaces them with scar tissue, leaving smooth, shiny patches of permanent hair loss. Because the scarring is irreversible, early recognition matters here more than almost anywhere else on the body.
Genital Lichen Planus
Genital lichen planus can appear on the vulva, vagina, or penis. On the vulva, the erosive form is most common, showing up as well-defined, glossy red patches on the inner labia and vaginal opening. These areas look glazed or raw, and the surrounding skin may show the same white lacy pattern seen in oral disease. On the penis, lichen planus more often resembles the classic purplish, flat-topped bumps, typically appearing on the glans in a ring-like pattern.
How Lesions Change Over Time
Lichen planus often resolves on its own within one to two years, though recurrences are common. During healing, the raised bumps gradually flatten, and the purple color fades. What’s left behind is typically a patch of darker skin (hyperpigmentation) that marks where the bumps once were. In lighter skin, these marks may be brown or grayish. In darker skin, the post-inflammatory color change can be quite pronounced and slow to fade.
Active lesions and healing lesions often coexist on the same person. You might see fresh purple bumps on one wrist while older, flattening patches with brown discoloration appear on the other. This mix of stages at different sites is typical and doesn’t mean the condition is getting worse. It reflects the natural, uneven pace at which lichen planus runs its course across the skin.