Homosalate is one of the most commonly used UVB filters in sunscreens in the US market. It belongs to the class of salicylates and has a peak absorption at 306 nm. The FDA approves a maximum concentration of 15%. Like other salicylates, such as octyl salicylate, it is a weak absorbent and is often combined with other organic absorbents.
homosalate
Octocrylene is another widely used UVB filter. This molecule works uniquely in stabilizing Avobenzone, the only long range organic UVA filter in the US. Without octocrylene, avobenzone degrades 50% after 1 hour of UV exposure, reducing the effectiveness of the sunscreen. Octocrylene has a viscous oily texture with peak absorption at 303 nm (range 290–360 nm).
Padimeter O
Q50.2 Para-aminobenzoic acid (PABA) was one of the first widely used chemical sunscreens. However, its use in modern sunscreens is limited for a number of reasons. This UVB filter requires an alcohol medium, which can stain clothing and cause a number of adverse reactions, including subjective stinging and allergic contact dermatitis. Ester derivatives, primarily padimate O (octyldimethyl PABA), have become more popular due to their better compatibility in various cosmetic vehicles and their lower potential for staining or other adverse reactions. Although PABA is an effective UVB absorber, problems with its formulation have limited its use. Padimate O is the most effective UVB absorber approved by the FDA. The decline in PABA usage and the need for higher SPF products has led to the incorporation of multiple active ingredients in a single product to achieve the desired SPF.
Octinoxate (octyl methoxycinnamate)
Q50.2 Cinnamate largely replaced PABA derivatives as the second most effective UVB absorber. Octinoxate (octyl methoxycinnamate, OMC) is the most commonly used sunscreen ingredient. As shown in Figure 50.2, which shows the absorbance curve on a logarithmic scale, OMC is an order of magnitude less potent than padimate O.
Caprylic acid (octyl salicylate)
Octyl Salicylate is used to enhance UVB protection in sunscreens. Salicylates are weak UVB absorbers and are often used in combination with other UV sunscreens. Other salicylates need to be used in higher concentrations.
Ensulizole (Phenylbenzimidazole Sulfonic Acid)
Most chemical sunscreen ingredients are oils that are soluble in the oily phase of emulsion systems, which partly explains the heavy, greasy aesthetic properties of many of these products. Phenylbenzimidazole sulfonic acid is water-soluble and is used in formulations that feel lighter and less greasy, such as cosmetic moisturizers for daily use.