sex work vs world's oldest profession

sex work

noun
  • Any job in which sex or eroticism is involved, especially prostitution or pornography. 

  • My mother distributes condoms and outreach materials to those that do sex work for a living in the Tenderloin and Mission. 

world's oldest profession

noun
  • Prostitution. 

How often have the words sex work and world's oldest profession occurred in a corpus of books? (source: Google Ngram Viewer )