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He could be having androgenic alopaecia. There are other possible causes like dandruff, autoimmune disorders
which can cause the same picture but better to get examined by a Dermatologist
to find the right cause and treat accordingly. There are various hair growth solutions which are very effective for androgenic alopaecia like Minoxidil
2% solution which the Dermatologist can prescribe. Also there is permanent solution of hair transplant
which is expensive.