You can prevent further greying of hairs...As a person ages, the melanin pigment of the hair decreases gradually, which causes graying of hair. Nowadays it is very common for the people under the age groups of 35 to have gray hair. The natural colour of hair is due to the cells in the hair follicles known as melanocytes which generate a pigment which gives colour to the hair. When melanocytes stop producing these pigments, due to increasing age,decreased nourishment,protein deficiency etc your hair starts to lose its natural colour which leads to graying of hair. Though one cannot prevent the natural cycle of whitening of hair, but you can always prevent your hair from premature graying...Consult nearest dermatologist they will do the needful.