Hi Arpita, Welcome to HealthcareMagic Forum.
Does he have any other symptoms like, Changes in skin pigment, Decreased muscle mass, Diarrhea
, Failure to gain weight and grow, Fatigue, Large belly??? If yes, he needs a Further evaluation by a Pediatrician
to rule out if he has Kwashiorkor, It is a form of malnutrition
that occurs when there is not enough protein in the diet. He will require a Urinalysis
and Blood work up. Apart from grey hair, if he has no other symptoms, Then the cause may be hereditary, that is, it may run in families. It is always better you get him evaluated by a Dermatologist
Feed him more calories and Protein rich diet which should include, eggs, chicken, milk, Fish, fresh fruits and Green leafy veggies. Calories are given first in the form of carbohydrates, simple sugars, and fats. Proteins are started after other sources of calories have already provided energy. Vitamin and mineral supplements will also be needed.
I Wish him Good Health, Take Care.