01.02.08
Meeting Consumer Needs in Water-Resistant Sunscreens
Together with film-forming polymers, a novel thickener affords greater utilization of inorganic UV filters in water-resistant sunscreen products.
Jennifer Davis
National Starch Personal Care
Bridgewater, NJ
Aware of the damaging effects of prolonged sun exposure, consumers reach for high SPF water resistant sunscreen products in ever-increasing numbers. They want the security of a higher SPF sunscreen and the confidence that these products will remain effective after a swim in the ocean or a jog on the beach. Particularly in the U.S., high SPF water resistant sunscreens have proliferated in the marketplace. Unfor-tunately, formulation constraints and FDA regulated actives limit the options formulators have in addressing these consumer needs. Inorganic UV filters like zinc oxide and titanium dioxide—both of which provide broad spectrum UV protection—have generated limited use because they can be difficult to adequately disperse in finished formulations. A lack of compatibility between select rheology modifiers and the inorganic UV filters has further limited their application in water resistant sunscreen formulas. This article looks at film forming polymers and a novel thickener that together afford greater utilization of inorganic UV filters in water-resistant sunscreen products.
Challenges and Opportunities
Inorganic and organic UV filters have a long history of safety, yet both technologies can beset formulators with technical challenges. Like avobenzone, inorganic UV filters offer broad-spectrum protection, however, inorganic particulates offer both photostability and chemical stability in finished products. Avobenzone, on the other hand, exhibits well-documented photo-instability, especially in combination with other select organic UV filters. Inorganic filters come with a different set of formulation challenges. Insufficient suspension and dispersion can cause deterioration of their UV-blocking ability as well as long-term formulation stability issues. For these reasons, formulators may be reluctant to use inorganic UV filters in formulations. However, with the implementation of a new UVA test method in the FDA final monograph for sunscreens, the broad-spectrum capability of inorganic particulate filters may prompt a renewed interest in zinc oxide and titanium dioxide. A new option to incorporate inorganic UV filters in many water resistant sunscreen formulations is contingent upon alternative thickener technology. If a novel thickener can support the integrity of SPF values in both storage and use, then inorganic filters can be included within formulations at a higher level of confidence than has been historically the case. Traditionally, xanthan gum is used as a thickener for sunscreens containing inorganic UV filters. Yet when it comes to formulating high SPF water-resistant products that consumers prefer today, research suggests that xanthan gum provides no synergistic effect with the polymer technologies that lend water-resistance to sunscreens.
An alternative to xanthan gum is commercially available today. Dehydroxanthan gum (Amaze XT polymer), a naturally derived, physically modified, water-dispersible xanthan gum is very easy to incorporate within sunscreen formulas. Excellent suspension capability, low tack and a unique rheology profile provide for its use as a thickener in formulations containing inorganic UV filters. In an aqueous solution, dehydroxanthan gum provides 30000cps viscosity (at 1%).
Dehydroxanthan gum is distinct in that it also has the ability to form films. When used in combination with other water dispersible film forming polymers, the polymer technology enhances the overall water resistance of formulations containing organic and inorganic sunscreens. A sample test formulation (Water Resistant Formula 1) made with 0.5% of dehydroxanthan gum and 4.4% acrylates copolymer (Dermacryl AQF polymer) demonstrates a substantially higher SPF value than a nearly identical test formulation, wherein 0.5% of xanthan gum is substituted for the dehydroxanthan gum—proof that the alternative technology combination helps to better disperse the inorganic UV filters throughout the sunscreen film and retain the actives on skin.
Water Resistant Formula 1
Ingredient %Wt.
Phase A
Arlamol HD (Croda) 1.5
(Isohexadecane)
Finsolv (Innospec) 3
(C12-15 alkyl benzoate)
DC 245 Fluid (Dow Corning) 2.25
(Cyclopentasiloxane)
Span 60 (Croda) 1
(Sorbitan stearate)
Arlacel 165 (Croda) 2
(Glyceryl stearate and PEG-100 stearate)
Neo Heliopan 303 (Symrise) 2
(Octocrylene)
Neo Heliopan AV (Symrise) 7.5
(Ethylhexyl methoxycinnamate)
Neo Heliopan BB (Symrise) 3
(Benzophenone-3)
Spectraveil (Croda) 6
(Zinc oxide and C12-15 alkyl benzoate and polyhydroxystearic acid) (~59.5% ZnO)
Phase B
Water 53.34
Amaze XT (National Starch) 0.5
(Dehydroxanthan gum)
Dermacryl AQF 45% (National Starch) 4.4
(Acrylates copolymer)
Glycerin 3
Tioveil AQ-N (~30%) (Croda) 7
(Titanim dioxide and alumina and silica and sodium polyacrylate)
Phase C
Dry-Flo AF Pure (National Starch) 2
(Corn Starch modified)
Glydant Plus Liquid (Lonza) 0.6
(DMDM hydantoin and iodopropynyl butylcarbamate)
Citric acid (50% sol.) q.s. to pH 7
Four additional formulations with slight alterations to Formula 1 were tested. As a negative control, the water dispersible film forming polymer (acrylates copolymer) was removed, leaving the 0.5% dehydroxanthan gum. PVP/Eicosene copolymer, an oil dispersible film forming polymer, was added to Formula 1 in place of acrylates copolymer at equal solids. The third additional formulation substituted xanthan gum for dehydroxanthan gum at equal solids, to investigate the effects of this combination with PVP/Eicosene copolymer. Finally, the acrylates copolymer in Formula 1 was replaced with another water dispersible film forming technology, PPG-17/IPDI/DMPA copolymer.
After an 80 minute immersion in water, Formula 1 containing both dehydroxanthan gum and acrylates copolymer exhibited an in-vitro SPF value of 32.6, a value significantly higher than the 20.5 measured in the substitute formula containing xanthan gum as the rheology modifier. The negative control formulation containing only dehydroxanthan gum exhibited no water resistance, as does the formulation containing PVP/Eicosene copolymer. The formulation containing the PPG-17/IPDI/DMPA copolymer showed similar performance to Formula 1. The data demonstrate that when combined with select water dispersible film forming polymers, dehydroxanthan gum enhances the water resistance of sunscreens containing both organic and inorganic UV filters (Table I).
Table I: In-Vitro SPF Results of Test Formulation 1 and Modification Formulations
Pre-Immersion Post-Immersion
SPF SPF
Amaze XT & Dermacryl AQF polymers 47.9 32.6
Xanthan gum & Dermacryl AQF polymer 49.8 20.5
Amaze XT polymer only 33.9 8.7
Amaze XT & PVP/Eicosene copolymer 52.9 5.8
Xanthan gum & PVP/Eicosene copolymer 54 7
Amaze XT & PPG-17/IPDI/DMPA copolymer 50.6 28.5
Efficacy with Age
Shelf life is one of the most important attributes associated with formulation efficacy. High quality water resistant sunscreens will maintain a relatively constant SPF value over time. Aged samples demonstrate the long-term stability of these formulations. Formula 1 described above containing both dehydroxanthan gum and acrylates copolymer—evaluated after three months in a 45ºC oven—shows similar SPF values and retention when compared to a sample aged in controlled room temperature conditions. The combination of dehydroxanthan gum and acrylates copolymer continues to maintain the SPF value after three months, before and after immersion in water. The results demonstrate that dehydroxanthan gum prevents agglomeration of the particulate UV filter after accelerated elevated temperature aging (Table II).
Table II: In-Vitro SPF Results of Test Formulation 1—Aged Samples
Pre-Immersion Post-Immersion
SPF SPF
Amaze XT Dermacryl AQF polymer 50.5 30.4
Amaze XT Dermacryl AQF polymer (aged) 56.1 36.6
Synergy with Select Polymers
Using a combination of water dispersible polymers, it is possible to boost the overall SPF value of a very water resistant test formulation. With in-vitro data demonstrating that the SPF value of Formula 1 will differ with the substitution of various thickeners and film forming polymers, three of the formulations were submitted for in-vivo SPF testing. Adding dehydroxanthan gum as the thickener technology in lieu of xanthan gum substantially boosted the in-vivo SPF values of Formula 1, both pre-immersion and post-immersion. Following the Very Water Resistant (80 minute immersion) FDA monograph protocol on a limited number of subjects, the combination of dehydroxanthan gum and acrylates copolymer delivered a pre-immersion SPF value of 29, a full 10 points higher than the combination of xanthan gum and acrylates copolymer. A similar spread is seen in post-immersion SPF values (Table III).
Table III: In-Vivo SPF Results of Substituted Thickeners
Pre-Immersion Post-Immersion
SPF SPF
Amaze XT & Dermacryl AQF polymers 29 27
Xanthan gum and Dermacryl AQF polymer 19 19
Amaze XT polymer only 10 9
A second test formulation indicates that the benefit of dehydroxanthan gum in water resistant sunscreens is not limited to its synergy with acrylates copolymer technology. Formula 2 containing acrylates/octylacrylamide copolymer as the water resistant film forming agent also shows a boost in the performance attributes of sunscreens when combined with dehydroxanthan gum. This combination delivered a pre- 80-minute immersion in-vitro SPF value of 46.8 and a post-immersion SPF value of 36.6.
Water Resistant Formula 2
Ingredient %Wt.
Phase A
Arlamol HD (Croda) 1.5
(Isohexadecane)
Finsolv TN(Innospec) 3
(C12-15 alkyl benzoate)
DC 245 Fluid (Dow Corning) 2.25
(Cyclopentasiloxane)
Span 60 (Croda) 1
(Sorbitan stearate)
Arlacel 165 (Croda) 2
(Glyceryl stearate and PEG-100
stearate)
Neo Heliopan 303 (Symrise) 2
(Octocrylene)
Neo Heliopan AV (Symrise) 7.5
(Ethylhexyl methoxycinnamate)
Neo Heliopan BB (Symrise) 3
(Benzophenone-3)
Spectraveil (~59.5% ZnO) (Croda) 6
(Zinc oxide and C12-15 alkyl benzoate
and polyhydroxystearic acid)
Phase B
Water 53.34
Amaze XT (National Starch) 0.7
(Dehydroxanthan gum)
Dermacryl 79 (National Starch) 2
(Acrylates/octylacrylamide copolymer)
Glycerin (JT Baker) 3
Tioveil AQ-N (~30%) (Croda) 7
(Titanim dioxide and alumina
and silica and sodium polyacrylate)
TEA 99% (triethanolamine) 0.71
Phase C
Dry-Flo Pure (National Starch) 2
(Aluminum starch octenysuccinate)
Glydant Plus Liquid (Lonza) 0.6
(DMDM hydantoin and
iodopropynyl butylcarbamate)
Citric acid (50% sol.) q.s. to pH 7
The results of this substitution underscore the flexibility formulators have in tailoring products to meet consumer needs. While it is not likely that we will see a substantial number of new FDA regulated sunscreen actives in the years ahead, formulators actually have a number of tools at their disposal to make efficacious sunscreen products that meet consumer expectations in areas like enhanced water resistance properties, enhanced SPF values and broad spectrum protection.
Optimizing Formulations
With the advent of dehydroxanthan gum, it is no longer a technical challenge to incorporate inorganic particulate UV filters within water resistant sunscreen formulations. Not only does the technology suspend particulates in formulation and prevent agglomeration, its film forming capability works in conjunction with other select forms of water dispersible film forming polymers to improve the water resistance properties of the finished formulation and deliver higher SPF values. This creative application of polymer blends allows the formulator to achieve a range of product and marketing goals using only inorganic broad-spectrum UV filters.
The benefits of using select combinations of film-forming polymers include:
• The ability to enhance water resistance of inorganic particulate UV filters;
• The ability to produce efficacious formulations based only on inorganic filters;
• The ability to produce formulations with high SPF values; and
• The ability to produce formulations with low tack and a light, non-waxy after feel.
Test Formula 3 made with particulate UV filters and a combination of dehydroxanthan gum and acrylates copolymer demonstrates the relative ease in which inorganic only water resistant sunscreen formulations can be made efficacious. Following the FDA monograph and protocol for very water resistant sunscreens on a limited number of subjects, formula 3 demonstrated an in-vivo SPF value of 23.9 before immersion and 22.8 after 80 minutes. The relatively constant SPF value maintained after 80 minutes is proof that the polymer blends help to retain particulates on skin.
Water Resistant Formula 3
Ingredient %Wt.
Phase A
Arlamol HD (Croda) 1.5
(Isohexadecane)
Finsolv TN (Innospec) 3
(C12-15 alkyl benzoate)
DC 245 Fluid (Dow Corning) 2.25
(Cyclopentasiloxane)
Span 60 (Croda) 1
(Sorbitan stearate)
Arlacel 165 (Croda) 2
(Glyceryl stearate and PEG-100
stearate)
Spectraveil FIN (~59.5% Zno) (Croda) 20
(Zinc oxide and C12-15 alkyl
benzoate and polyhydroxystearic
acid)
Phase B
Water 38.75
Amaze XT (National Starch) 0.5
(Dehydroxanthan gum)
Dermacryl AQF (National Starch) 4.4
(Acrylates copolymer)
Glycerin (JT Baker) 3
Tioveil AQ-N (~30%) (Croda) 23
(Titanim dioxide and alumina
and silica and sodium polyacrylate)
Phase C
Glydant Plus Liquid (Lonza) 0.6
(DMDM hydantoin and
iodopropynyl butylcarbamate)
Citric acid (50% sol.) q.s. to pH 7
Formulators and marketers in search of new options to address consumer requirements need look no further than these polymer blends. The combination of dehydroxanthan gum and acrylates copolymer allows formulators to achieve formulation goals that are not otherwise possible with traditional thickeners, such as xanthan gum (Table IV).
Table IV: In-Vivo SPF Results Inorganic Filters Only
Pre-Immersion Post-Immersion
SPF SPF
Amaze XT & Dermacryl AQF polymers 23.9 22.8
(inorganic filters only)
Unlike other thickeners, dehydroxanthan gum is able to suspend particulate UV filters and provide some film formation. Blending this technology with select water dispersible polymers, such as acrylates copolymer, provides a boost in SPF values and water resistant properties.
Conclusions
Dehydroxanthan gum (Amaze XT polymer) provides a new level of formulation freedom for makers of inorganic UV filter-containing sunscreens. The polymer is proven to suspend particulate UV filters in formulation very easily and efficiently. Aged samples indicate formulation efficacy after three months, demonstrating a constant SPF value as seen via in-vitro measurements. When combined with select forms of water dispersible film forming polymers, such as acrylates copolymer (Dermacryl AQF polymer), or acrylates/octylacrylamide copolymer (Dermacryl 79 polymer), dehydroxanthan gum enhances the water resistance properties of test sunscreen formulations.
Dehydroxanthan gum gives a higher in-vivo SPF value than formulations containing xanthan gum when it is combined with acrylates copolymer (Dermacryl AQF polymer). Efficacy is demonstrated in both pre- and post-immersion values. In sunscreens made solely with inorganic UV filters—zinc oxide and titanium dioxide—select combinations of polymers also enhance water resistant properties, and this can be seen with in-vivo data.
Formulators now have the ability to produce efficacious sunscreens that cater to major consumer demands in areas such as water resistance, higher SPF values and broad-spectrum protection. Just as importantly, formulations containing combinations of organic and inorganic UV filters, or only inorganic UV filters can be made without technical challenges, given the compatibility and synergies that come with select polymer blends.