Biochemistry of human axilla malodor and chemistry of deodorant ingredients

Key human axilla malodorants are hexenoic acid (3) and 3-hydroxy-3-methyl-hexanoic acid (5), accompanied by some 25 structurally related hydroxyalkanoic acids and alkenoic acids. These sweat acids are secreted in the axilla in the form of odorless glutamine conjugates and are released upon enzymolysis by AMRE (Axillary Malodor Releasing Enzyme), produced by Corynebacteria. The sulfanylalkanols 8-11 represent another important group of axilla malodor compounds that are also secreted in the form of odorless precursors. The major precursors are cysteine-glycine sulfanylalkanol conjugates of type 14 and the minor precursors are cysteine sulfanylalkanol conjugates like 15. The release occurs upon action of a beta-lyase of axilla bacteria. Besides the classical approaches of axilla malodor masking using fragrances, the use of chemicals to neutralize malodorants is described. The elucidation of the biochemistry of the sweat acid release has. allowed the development of fragrance precursors that act as competitive substrates to the natural malodor precursors as well as the development of specific antagonists that block AMRE. Finally, the characterization and functional expression of a first human malodor receptor presents an interesting approach for future development of axilla malodor blockers.