The null hypothesis (H0) in this study could be formulated as follows: "There is no significant difference in the effectiveness of the four different body lotions when applied to unique body locations daily for two weeks."
In statistical terms, if we denote the effectiveness of the lotions as a dependent variable, the null hypothesis could be expressed as there being no significant difference in mean effectiveness across the four lotions.
It's important to note that the null hypothesis is a statement of no effect or no difference, and the goal of the study would be to either reject or fail to reject this null hypothesis based on the collected data and statistical analysis.