Baby (Powder) It.

This is the oldest trick in the greasy hair book. Sprinkle a teeny tiny bit of baby powder on your roots, wait a second for it to soak up the oil, and then brush it out. Women with dark hair might want to try a pigmented hair powder, but you can also use a bit of powder makeup, dabbed onto your roots with a loose makeup brush, for the same effect.

Johnson's Baby Powder, $7, Amazon