Waterproof enhancing technologies (WET) are critical ingredients used to increase the wash, sweat, migration, transfer, sand, and rub resistance of sunscreen formulations. Often these technologies can also be used to boost SPF and reduce the skin penetration of chemical sunscreens. WET are normally used at a 1-3% active level in formulations depending on the type of application and formulation.
The performance of WET can be highly variable depending on the type of formulation and its inherent wash resistance. The goal of the formulator should always be to employ the most efficient technology to keep the use level to a minimum since WET can have a negative impact on skin feel.
Balancing performance with skin feel tradeoffs is key. The use of high hydrophilic-lipophilic balance (HLB) emulsifiers, highly hydrophilic ingredients like polyols, and water-soluble sunscreens like Phenylbenzimidazole Sulfonic Acid should be kept at a minimum for optimal results. It is even possible to formulate waterproof SPF formulations through good formulation design without using any technology.
The main chemical classes used in WET include:
- oil and water-soluble film-forming polymers
- latex-based water-dispersible polymers
- waxes/resins
- emollients
The types of technologies used in the marketplace suggest that they function by forming highly hydrophobic films on skin in which the sunscreens are either soluble or dispersed uniformly within the residual film on skin. The type of technology used in products is very dependent on the type of formulation.
Looking for waterproof materials?
UL Prospector® offers listings for waterproof materials, from emulsifiers to UV absorbers and more. Find technical data, request samples, and contact global suppliers – all right within Prospector.
Register today for access!
The most common recreational sunscreens currently sold are aerosol/non-aerosol anhydrous sprays which use Acrylates/Octylacrylamide Copolymer as the main waterproofing polymer. Other common technologies used include VA/Butyl Maleate/Isobornyl Acrylate Copolymer and Styrene Acrylates Copolymer. “Sport” type spray formulations positioned for more demanding physical activity frequently use higher levels of actives and combinations.
The most common emulsion-based SPF products are oil in water dispersions using Styrene/Acrylates Copolymer, Acrylates/C12-22 Alkyl Methacrylate Copolymer, and VP/Eicosene Copolymer. Frequently better results can be achieved using combinations of WET. Good results can be achieved with most chemical classes of WET when used in an optimized formulation.
The historical WET benchmark is VP/Eicosene Copolymer, which has been used for over 30 years. Results, however, can be highly variable and formulations can feel tacky when using 2% or higher concentrations.
In vivo performance testing
In order to meet the FDA Sunscreen Monograph, sunscreen products making water resistance claims must maintain their claimed SPF for 2/20 minute sessions of moderate water activity to be labeled water resistant and 4/20 sessions to be labeled very water resistant1. Good products can maintain 80-100 percent of their static SPF in a very water-resistant test. Normally very water-resistant products also have good sweat resistance.
In vitro performance testing
The static in vitro SPF is determined in triplicate using ether Poly(methyl methacrylate (PMMA) plates or a collagen substrate. A positive control is also run that has known in vivo static and water-resistant SPF results. The control should be similar to the type of vehicle used in the developmental formulation.
- Prepare samples in triplicate and place in a glass cylinder filled with tap water at a temperature of 25°
- Use a propeller mixer to stir the water for 80 minutes at a constant RPM.
- Remove the samples, allow to air dry, and perform the in vitro SPF. Excellent correlation with in vivo results is normally achieved.
Waterproof sunscreen formulation tips
- Use hydrophobic-coated metal oxides to provide better wash resistance
- Develop and use an in vitro waterproof screening method.
- Good results can normally be achieved in all types of vehicles; oil in water, water in oil, sticks, oils, and hydroalcoholic formulations. I believe that the best results are obtained in formulations containing volatile solvents like water or Ethanol.
- Make sure that your crystalline sunscreens like Avobenzone and Oxybenzone don’t crystalize in product or on skin during use. A good screening test is to place the product oil phase without volatiles or waxes at -15°C and check for crystals at room temperature.
- WET should be evaluated using 2% active. Try to use ingredients that also have an SPF-boosting effect.
- Use Potassium Cetyl Phosphate/Hydrogenated Palm Glycerides, Cetyl Phosphate neutralized using TEA or Aginine as a primary o/w emulsifier
- Think of combinations to improve SPF, skin feel, and reduce the level of active needed.
- Develop surfactant-free, sterically-stabilized oil in water emulsions to improve the inherent wash resistance formulations and reduce the level of WET needed. These dispersions typically use a hydrophobically-modified acrylate polymer (Acrylates/C10-30 Alkyl Acrylate Crosspolymer) as an emulsifying/stabilizing agent and low levels of VP/Eicosene Copolymer to reduce the particle size of the oil droplets. Excellent water-based SPF sprays can be developed using this approach.
References
- FDA.gov: Code of Federal Regulations Title 21, Capter I, Subchapter D, Part 352: OTC Sunscreen Drug Products
The views, opinions and technical analyses presented here are those of the author or advertiser, and are not necessarily those of ULProspector.com or UL Solutions. The appearance of this content in the UL Prospector Knowledge Center does not constitute an endorsement by UL Solutions or its affiliates.
All content is subject to copyright and may not be reproduced without prior authorization from UL Solutions or the content author.
The content has been made available for informational and educational purposes only. While the editors of this site may verify the accuracy of its content from time to time, we assume no responsibility for errors made by the author, editorial staff or any other contributor.
UL Solutions does not make any representations or warranties with respect to the accuracy, applicability, fitness or completeness of the content. UL Solutions does not warrant the performance, effectiveness or applicability of sites listed or linked to in any content.
This explains, why I use sun protection clothing and NEVER will allply any such sunscreen formulations to my skin.
Hydropobic coated metal particles, TEA, benzones, silanes etc. in formulation that even acrylate polymers are made shin permeable ???
Cosmetic Industry and users seem not to be well informed
Biologist
I find it concerning that you are still promoting the use of oxybenzene and avobenzenone when they have been restricted or banned for use due to the detrimental environmental impact they are having on coral reefs. Oxybenzene is also a known endocrine-disrupting compound (EDC).