Coal forms from the accumulation of plant debris, usually in a swamp environment. When plant debris dies and falls into the swamp the standing water of the swamp protects it from decay. Swamp waters are usually deficient in oxygen, which would react with the plant debris and cause it to decay.
Porokeratosis is generally considered to be a benign condition though malignant transformation has been seen in all but the punctate variety, necessitating regular followup of patients with porokeratosis (Maubec et al., 2005; Sasson & Krain, 1996).
When we talk about Lichenoid keratosis, we are dealing with a skin problem. Lichenoid keratosis is small skin lesion that usually appears on the arm, hands and the chest. Lichen kerotosis is usually a solitary lesion which appears similar to a solar lentigo (freckles). It is easy to recognize lichenoid keratosis lesion from its red to grey color.