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).
keratosis, seborrhoeic. Lesion of the skin appearing as brown or yellowish thickening of the skin of the face, eyelids and/or conjunctiva. It is common in the elderly and may be a precursor to squamous cell carcinoma.Management includes cryotherapy, local surgical excision or radiotherapy.esion of the skin appearing as brown or yellowish thickening of the skin of the face, eyelids and/or conjunctiva. It is common in the elderly and may be a precursor to squamous cell carcinoma. Management includes cryotherapy, local surgical excision or radiotherapy.