How many letters does the top answer for “a blemish on the skin that is formed before birth” have?

The most common answer is birthmark (9 letters).

Crossword clue: a blemish on the skin that is formed before birth

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

birthmark 9 letters wn-def

a blemish on the skin that is formed before birth

nevus 5 letters wn-def

a blemish on the skin that is formed before birth