Effectiveness of sunscreens and factors influencing sun protection: a review

The effectiveness of sun protection depends directly on the photo-protective product employed, the way it is used and the amount applied. Many studies report that sunscreens are often applied incorrectly, at amounts much lower than those recommended for the sun protection factor (SPF) specified on the label. When not used properly, the effectiveness of the product against sun exposure damage is reduced. Currently, sunscreens are available in a variety of different formulations and types, such as stick (bar), aerosol, cream, lotion, oil, tanning formulations and makeup. However, developing an effective stable photo-protective formula that can be correctly applied regardless of type poses a challenge, as effectiveness is dependent on several factors. Factors influencing effectiveness include sun exposure conditions (direct or indirect), level of protection (SPF), amount of product applied, maximum exposure period before reapplication, product type (spray, lotion, etc.), layer thickness required, coverage, and ability to spread and permeate into the skin. Studies comparing the effectiveness of different forms of sunscreens, the amount of product applied by consumers and SPF and UVA protection determined by validated methodologies, are lacking. Therefore, the objective of this study was to review the available literature on the topic and discuss the effectiveness of sunscreen formulations and factors influencing sun protection. This review was carried out on the scientific databases MEDLINE, PubMed and Scielo. Of the many publications retrieved, thirty-nine articles most relevant for this review were selected.