The process of developing and testing a sunscreen is not unusually difficult but it does require close attention to the regulations and coordination with the testing laboratory preparing the efficacy data.
Sunscreens may be part of a cosmetic line and those that are intended to provide protection from incidental sun exposure during the normal day’s activities are often called “cosmetic sunscreens”. On the other hand, sunscreens intended to provide protection from prolonged sun exposure activities such as beach, pool, or other activities where sun exposure is high and resistance to water or perspiration is required. These products are often called “active or sport” formulations. The formulation requirements for each class are slightly different but the underlying regulations for the products are the same.
In the United States, sunscreens and several other categories of functional products are regulated under the over-the-counter (OTC) drug regulations of the Food and Drug Administration (21 CFR 352). These regulations define the allowable active ingredients (termed UV filters) and their maximum use concentrations, the performance testing required to establish the efficacy of the product (SPF, Broad Spectrum coverage, and water resistance), and labeling of the product.
An important concept of the OTC program is that the active ingredients used in the formulation will be considered safe provided that the regulations are followed. Therefore, the individual new formulation does not require approval from FDA. The specific OTC drug regulations for sunscreens are unique to the United States, but many of the same principles apply in many markets. In the European Union, sunscreens are regulated as cosmetics (for labeling) but certain restrictions for active ingredients and testing apply.
In all major markets, the active ingredients that can be used as UV filters are prescribed by positive lists (that is, only ingredients on the specific list for that market may be used). The maximum concentration of each active ingredient is also indicated. These lists for both specific ingredients and maximum concentrations are not the same across markets. Thus, a product prepared for one market may well not be acceptable in another. For example, the United States has a shorter list of approved UV filters than does the EU and so many EU products are excluded from the U.S. market.
A functional sunscreen formulation is not simply the sum of its active ingredients. If it were, efficacy testing would be rather easy. The remaining ingredients, termed inactive ingredients under the regulation, are essential not only for the aesthetics of the product but for its efficacy as well. To function effectively, the formulation must hold the UV filters in a film on the surface of the skin. The film holds the UV filters to form a “tortuous path” through which the UV light must pass. The filters scatter and absorb the UV light attenuating exposure to the skin below. Since the surface of the skin is not flat, the formulation must form a film that can cover the skin peaks and valley to block the UV light.
While the formation of a surface film is required for function, it can impact product esthetics. Cosmetic sunscreens, such as facial moisturizers, are intended for incidental UV exposure with limited water or perspiration exposure. These products may be successful with less robust film former. Active or sport formulation require considerable water resistance (once they have dried on the skin) and so need more robust, less water-soluble film formers.
In summary, to ensure regulatory compliance of OTC sunscreen formulations, it’s important to closely follow the regulatory and testing requirements.