Investigations will be performed to determine the effect of composition on the internal structure of semi-solid oil-in-water emulsions designed to model the GlaxoSmithKline Physiogel range of skin care products. The model creams studied will involve essential structural components only, viz., chemically pure surfactant/co-surfactant emulsifier, and water, but with added (hydrogen- or deuterium-labelled) preservative. The latter is added to prevent microbial contamination of the creams but is also found to cause detrimental changes in long-term stability. The studies will be performed on systems with varying emulsifier composition, prepared with and without preservative, both fresh and after 1-month's storage. By such means, we aim to determine the changes in structure that manifest over time due to changes in emulsifier composition, and also those due to addition of preservative.