The solution of water and sucrose is fertile ground for colonies of microorganisms, raising risks for the product. But the hydrophilic properties of sugar also make them resistant to microbial growth. The syrup medium needs to strike a balance between viscosity and pathogen resistance.

A sucrose concentration of 85% or higher in cough syrups is considered microbe-resistant. In cases where the concentration is lower, you can counter pathogenic development with preservatives. A range of compounds such as glycerin, sorbic acid, and butylparaben are effective.