Frequent dying causes gray hair

The pigment in the hair called melanin determines the color of the hair.  Melanin is produced in the roots deep inside the skin. You dye the hair that is outside the skin which is basically dead tissue.  

No matter how many times you dye hair it does not harm the production factory present in the roots and thus does not affect the color of the hair. (Author by: "Doctor Khawar Nazir Dermatologist Lahore")