Ḍākinī and Śāṅkhinī are two companions of Lord Śiva and his wife who are supposed to be extremely inauspicious, having been born of ghostly life. It is believed that such inauspicious living creatures cannot go near a nima (neem) tree. At least medically it is accepted that nima wood is extremely antiseptic, and formerly it was customary to have a nima tree in front of one’s house. On very large roads in India, especially in Uttar Pradesh, there are hundreds and thousands of nima trees. Nima wood is so antiseptic that the Āyurvedic science uses it to cure leprosy. Medical scientists have extracted the active principle of the nima tree, which is called margosic acid. Nima is used for many purposes, especially to brush the teeth. In Indian villages, ninety percent of the people use nima twigs for this purpose.
Ref >> Srila Prabhupada Vani.