It is belief that worshipping hanuman in this form to alleviate troubles and keep evil forces away. It serves as a protection to devotees who chant with utmost faith is a representation of him, showing 5 faces, in different directions.
It is based on the incident in Ramayana, where Hanuman assumes the form to kill, Ahiravana, the king of Pathala, and Ravan's brother.
Note : Dnt Clean with harsh chemicals. Use traditional method ( Lemon, Tamarind ) to clean.