Iso-valeric Acid (IVA) is a common mal-odor that has the smell of "stinky feet". Our previous efforts have shown that IVA can be masked by sub-threshold perfume raw materials (PRMs) (Huang et al., 2022). However, whether this masking effect is mutual hasn't been studied yet. In this study, the interaction between IVA and PRMs was fully investigated using Sniff Olfactometery (SO) (Rochelle et al., 2017; Wyckoff & Acree, 2017). Four different PRMs were chosen as potential masking agents, s-limonene, neohivernal, florhydal and methyl iso-eugenol, to explor the interactions between each PRM and IVA. All 8 subjects' peri-thresholds for both IVA and PRMs were obtained by calculating the concentration where the detection probability of an odorant is 0.5 and one quarter of the peri-threshold concentration was treated as the sub- threshold concentration. We started from the threshold measurement, then based on these individual peri-threshold samples were prepared. The effect of sub-threshold concentration of a single PRM on the peri-threshold concentration of IVA was studied first to make sure we could reproduce our previous results (Huang et al., 2022) and to provide a reference for this study. Then the effects of a sub-threshold level of IVA on the peri-threshold levels of each single PRM was studied. On average, all sub-threshold levels of the PRMs could suppress the subjects' perception of peri-threshold IVA. However, the effect of the sub-threshold level of IVA on the peri-threshold levels of each PRM showed individual differences-, i.e., masking, synergy or little effect.