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).
Common Benign Growths Online Medical Reference - from diagnosis through treatment options. Co-authored by Justin G. Woodhouse and Kenneth J. Tomecki of the Cleveland Clinic. Seborrheic keratoses may be the most common benign tumor of the skin. Typically, they are scaly (hyperkeratotic), brown (hyperpigmented), often somewhat greasy plaques that vary in size and thickness and often appear to be stuck onto the skin surface (Fig. 1).