What is the reasons for the lack of growth of beard?

Beard growth: Since you don't list your age, I have to assume that you are young and have not yet had growth of facial hair. This could be for a variety of reasons. You may not be producing enough male hormone for this type of change to occur. If you are older and there is a decrease in beard growth the same or other factors may apply. Se your MD for evaluation and lab work if needed.