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Minerals

The Next Level in Mineral Sunscreens: Innovative Particle Technology

Sun care products are a 1.9 billion dollar a year industry in the U.S. alone — especially for broad-spectrum protection — and customers are demanding more natural products.

So why haven’t mineral-based sunscreens achieved greater market penetration? Aesthetic challenges are mostly to blame. However, breakthrough formulation technology is transforming the look and feel of mineral sunscreens without sacrificing UV protection.

High sensory expectations and changing UVA claims

Consumers have long complained about the whiteness or grittiness of sunscreens containing minerals like Zinc or Titanium — a result of metal oxide particle size and distribution. In one research study, a descriptive sensory analysis assessed the sensory properties of over 50 commercial sunscreen lotions with SPF claims of 30 or 50. Those that performed best for consumers had low gloss and “very low whiteness” after 20 minutes. (Interestingly, consumers accepted some whiteness during rub out, but wanted no residue afterwards.) 1

More countries are moving toward a single UVA performance criteria.

There’s another reason aesthetics matter: more countries are moving toward a single UVA performance criteria. This means companies have less room to stand out with numerical claims and must rely more on aesthetic perceptions of their products.

Particle distribution — and size — matter

Mineral dispersions tend to form agglomerates that decrease efficacy while simultaneously increasing whitening properties. These collections or groups of particles actually let in and scatter damaging UV light into the skin, and the look and feel leaves a lot to be desired. The effect appears in both TiO2 and ZnO formulations, although the issue is more severe in TiO2 formulations. In addition, TiO2 tends to be photocatalytic, promoting the formation of skin-aging reactive oxygen species and catalyzing the decomposition of organic materials. Uniform and narrow-size particle distribution is key to a smooth, elegant feel and low whiteness — but formulators can’t lose the mean particle size necessary for UV attenuation.

Innovative coatings manage particles

A new and proven approach to tightening overall particle size distribution is to coat the micronized TiO2 and ZnO particles in a concentrated form in a liquid dispersion. An effective coating system consists of silica moieties (derived primarily from tetraorthosilicate), alkyl groups (derived from triethoxycaprylylsilane) and polydimethylsiloxane (derived from dimethiconol). This combination forms a complete coating that surrounds the mineral particles and eliminates gaps. Chemical interactions between the particles are virtually eliminated and the particles no longer form clumps; they behave as individual entities. This quality also enhances flowability and smoothness desired by consumers, since particles “roll over” each other and aren’t forming structures resistant to flow.

“Chemical interactions between the particles are virtually eliminated and the particles no longer form clumps; they behave as individual entities”

For example, Hallstar’s zinc and titanium oxide dispersions (HallBrite® EZ-FLO ZDX, EZ-FLO ZDX Plus, EZ-FLO TDX, and EZ-FLO TDX Plus) feature proprietary and patented coating systems that eliminate agglomeration and create a smooth lotion consistency while also outperforming the competition on whiteness reduction. But these dispersions also maintain safe, high-performing broad spectrum protection without the synthetic sunscreens many consumers want to avoid (though the dispersions also work well with Avobenzone). With the addition of Hallstar’s industry-leading SolaStay® S1, the most powerful photostabilizer on the market, these innovative products are also exceptionally stable. It’s a triple win for beauty and personal care companies: efficacy, aesthetics and natural ingredients.

Not all mineral dispersants are alike

Manufacturers still have the option of adding powder directly to a formula, but it’s easy to see signs of agglomeration, and mineral powders can also be difficult to work with. In fact, developing the formula and simultaneously keeping particles well distributed is no easy task. Even when formulators turn to dispersants, their compatibility is sometimes limited to certain fluids. The dispersant must be designed for compatibility.

“Our mineral sunscreen dispersions are actually a combination of the coated particles and our HallBrite® BHB fluid—which has been described as pillowy and cushioning, enhancing the improved skin feel,” says Dennis Zlotnik, Senior Market Developer Manager at Hallstar. “This is a turnkey, final formula broadly chemical compatible across a range of oil and water formulas. It’s convenient for the formulator, and it’s better for the consumer.”

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Sources

1 Hewitt, Julian P. “Sunscreen formulation: optimizing aesthetic elements for twenty-first century consumers.” Eds. Wang, Steven Q., Lim, Henry W. Principles and practice of photoprotection. New York: Springer, 2016.

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