Lichen Planus is an allergic reaction triggered by problems centered on the body’s immune systems. Lichen Planus frequently appears as flat level bumps on the skin that is shiny and can have a reddish to a purplish color. Lichen Planus is an allergic reaction triggered by problems centered on the body’s immune systems. Lichen Planus frequently appears as flat level bumps on the skin that is shiny and can have a reddish to a purplish color.