In this paper, we deduct an alternative continuum description of smectic C liquid crystals with a consideration on the symmetry of molecular elastic interactions. With this expression, we reveal the intrinsic connection between molecular interactions and layer deformation, and establish a generic connection between the elastic constants and the layer deformation coefficients. While the continuum theory can be connected with molecular elastic interaction, the new expression should be more suitable to describe those "frustrated smectics" where layer structure is not clearly formed, which are very often observed in complex biologic systems. (c) 2006 Elsevier B.V. All rights reserved.Physics, Condensed MatterSCI(E)EI1ARTICLE1-2123-128...