In the name of Allah, the most Beneficent, the most Merciful.
Hair transplants consists of the redistribution of your naturally growing hair. Hair follicles growing at the back of the head are transplanted to the bald areas.
With regards to your question it is permissible to have hair transplants as long as your natural hair or synthetic fibres are being used. However, it should be borne in mind that if the transplant entails joining human hair to one’s hair, then this would be impermissible in Islam, as it involves deception and using a part of the human body, both of which are unlawful. (Fatawa Hindiyyah p.358 v.5)
Saaiduna Abu Hurairah Radiallahu Anhu narrates that the Prophet of Allah Sallallahu Alahi Wasalam has said:
“Allah has cursed the woman who joins (her or someone else’s) hair (with the hair of another man or a woman) and the woman who asks for her hair to be joined (with the hair of another person) and the one who tattoos (herself or someone else) and the one asks to get tattooed.” (Sahih Bukhari p.879 v.2)
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham.