Sunscreens are the most effective and widely available interventions for sun damage, other than sun avoidance or clothing. However, sun-screens vary widely in their ability to screen various UV wavelength components. Testing methods for sunscreens rely on UV-induced erythema to determine a sun protection factor (SPF), primarily a measure of UVB protection only. Determination of an immune protection factor (IPF) has been proposed as an alternative or adjunctive measure to SPF, and, indeed, recent studies show that the IPF can detect the added in vivo functionality of sunscreens--such as high levels of UVA protection--that the SPF cannot. Consensus on the definition of IPF, however, is required. Data are available on quantification of the IPF for restoring the afferent or induction arm of contact sensitivity, but other immune parameters also have been measured. A review of in vivo studies in humans, in which sunscreens are used to intervene in UV-induced modulation of immune response, cells, or cytokines, highlights the technical variables and statistical approaches that must be standardized in the context of an IPF for regulatory product claim purposes. Development of such IPF standards would allow the integration of both UVB and non-UVB solar wave-band effect-reversals. In addition, it could be applied to integrate the effects of other ingredients with protective function (ie, antioxidants, retinoids, or other novel products) and spur the development of more advanced and complete protection products.