Hi, Premature graying of hairs is very common problem. In your case it is limited to beard only. I think, it may be hereditary most probably. Genetic cause is inevitable. Other causes like thyroid dysfunction,anaemia, vitamin deficiencies, endocrinal diseases,internal diseases..etc may be ruled out. Stress and tension may also precipitate the the disease. Have nutritious food and avoid worries and stress. Local application of melatane gel for long time might improve. Calcium penthothanate tab may be taken for few years. Underlying cause may be treated. If no improvement, take it granted..and be remain happy. I hope you got my answer. Thanks. Dr. Ilyas Patel MD