'unblistered' originates from English, formed by the prefix 'un-' plus the past participle 'blistered' of the verb 'blister'.

'blister' changed from Middle English forms such as 'bleistre' or 'blistere' and eventually became the modern English word 'blister'; 'unblistered' was formed later by prefixing 'un-' to the past participle.

Initially, 'blister' referred to a bubble or swelling (a raised filled spot); over time it came to denote the raised sore on skin or surface, and 'unblistered' now means 'not having such blisters'.