Abstract: A synergistic antimicrobial composition for use in personal care products functions as an antifungal agent in hair shampoo and hair care products, and includes (A) an undecylenic acid based phosphobetaine depicted by Formula I, where R=Undecylenic acid: and (B) a sophorolipid, a biosurfactant produced by a fermentation process using Candida bombicola, having a structure as depicted by Formula II(A), Formula II(B), or a mixture thereof: