This only occurs in Leviticus 13 and 14 where it is used 14 times to describe bald or scaly patches of eruption on the skin. Such patches are generally the result of the action of parasitic organisms. The common form known now as scalled head is produced by a microscopic plant, Achorion schoenleinii. In Old and Middle English, scall was used for scabbiness of the head (Chaucer and Spenser). See also Skeat, Concise Etymol. Dict. of English Language.