lanugo vs vellus hair

lanugo

noun
  • Soft down or fine hair, specifically that covering the human foetus or a tumorous area. 

vellus hair

noun
  • Short, fine, light-colored, and barely noticeable hair that develops on most of a person's body from his/her childhood. 

  • An individual strand of vellus hair 

How often have the words lanugo and vellus hair occurred in a corpus of books? (source: Google Ngram Viewer )