Hi doctors Good evening my son is 3 years old. He has white patches only on his  face. And he bites his nails , toes and lick surfaces from past arround one month. He consistently bite his nails put fingers in mouth. Lick everyone body. What is the reason. Which vitamin deficiency may be he suffer... And his left knee produce crackling sound every time when he ride staircase upside . Every time, he goes upside on stairs clear cut cut sound listen only from left knee when pressure take on it to go up. What is the reason . Currently he is having only pediasure and nothing else. Guide me in  better way.