as a basic part of your qualities or characteristics.
She always seemed to be acting, but she had the theatre in her blood, and performing was as natural for her as breathing.
Related vocabulary: born to do something
in (one's) blood
Innate, as of a skill or quality. All of my relatives are doctors—medical prowess is just in our blood.She knows how to play. Music is in her blood.
in your blood
COMMON If something is in your blood, it is a very important part of you and seems natural to you, for example because it is traditional in your family or culture. Trilok has music in his blood. `I was born into a family of musicians.'The sea was in his blood — his father had been a marine.