n-Octyl 4-hydroxybenzoate-2,3,5,6-D4 is a labelled analogue of n-Octyl 4-hydroxybenzoate. n-Octyl 4-hydroxybenzoate is part of a family of compounds called parabens, which are commonly used in cosmetic formulations and are hypothesized to cause allergic dermatitis in humans. n-Octyl 4-hydroxybenzoate also has potential antifungal activity.