Many individuals claim that insect repellents offer them little protection. This article explains the factors that lead alternatively either to longer or to shorter protection times. In most instances, those factors leading to shorter protection times can be overcome by more generous and frequent applications of commercially available repellents.
Howard I. Maibach, Abdul A. Khan, William Akers. Use of Insect Repellents for Maximum Efficacy. Arch Dermatol. 1974;109(1):32–35. doi:10.1001/archderm.1974.01630010012002