['High-performance sunscreen protects both healthy consumers and photosensitive patients from strong ultraviolet (UV) exposure. The sun-protection factor (SPF), which indicates the efficacy of UV protection, is determined using a prescribed sunscreen application thickness of 2.0 mg/cm(2). Therefore, users should apply at least 2.0 mg/cm(2) of sunscreen to obtain the level of UV protection expected from a product. In most cases, however, users apply insufficient amounts of sunscreen.', 'To determine the amount of sunscreen applied under specific conditions, and the relationship between application thickness and SPF value in high-performance sunscreen.', 'The amount of applied sunscreen was calculated under practical conditions and conditions that directed a double application. The SPF values of high-performance sunscreen applied at three thicknesses (2.0, 1.0 and 0.5 mg/cm(2)) were determined according to the international SPF testing method. RESULTS. The relationship between SPF value and application thickness correlated in a logarithmic curve. The mean application thickness under practical conditions was approximately 1 mg/cm(2), and directing subjects to use a double application increased the application thickness to nearly 2 mg/cm(2).'] Is relationship between sun-protection factor and application thickness in high-performance sunscreen : double application of sunscreen recommended?