The discovery of high-$T_c$ superconductivity in sulfur trihydride (${\mathrm{H}}_3\mathrm{S}$) over a decade ago opened an exciting era of research on superconducting superhydrides; however, in spite of extensive studies, there remain unresolved issues concerning the structural stability and superconductivity of ${\mathrm{H}}_3\mathrm{S}$. Most conspicuous are large discrepancies between theoretical and experimental pressures for stabilizing the optimal high-$T_c$ phase and between calculated and measured $T_c$ values. Here, using first-principles calculations, we show that deviatoric stress and associated strain, omnipresent in experiments yet omitted in past theoretical treatments, can notably impact stability and $T_c$ of ${\mathrm{H}}_3\mathrm{S}$. These findings unveil stress-altered properties of highly compressed ${\mathrm{H}}_3\mathrm{S}$, offering a possible explanation for the disparity between theory and experiment. Moreover, this study showcases deviatoric stress as a viable mechanism for modulating material properties, which has important implications for high-pressure research across multiple scientific fields where nonhydrostatic pressure conditions are prevalent.

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• Lattice dynamics
• Pressure effects
• Superconductors
• Crystal structures
• Hydrides
• Density functional calculations
• Eliashberg theory