The Blues Scale is derived from major by lowering the third, fifth and seventh of the scale. This creates the “darker” sound we often associate with blues melody and improvisation, which very often is superimposed on major chords.
Although all the notes of the major scale are available for blues playing and have been creatively used, the blues scale is often presented as the first, lowered third, lowered fifth, perfect fifth, and lowered seventh of the the major scale.
Disclaimer: All content is the author’s interpretation of standard music theory, & should be confirmed & validated by your music trainer, tutor or appropriate professional.