Sunscreen selection

[saresha]

Studies have shown (yes, I finally found them!) that a mix of chemical and physical filters work better, though efficacy is highly dependent on what mix and what ratio. (More below.)

Synergy Between Actives
Using combinations of sun filters is a necessity to obtain the higher SPF values required so finding synergy between them is a rewarding operation... W. Johncock investigated mixtures of zinc oxide with octocrylene and with isoamyl p-methoxycinnamate and found significant increases in protection. Hewitt and Housley studied the synergy that may be obtained when using inorganic oxides in conjunction with OMC and other organics. Thomas Wünsch found a mixture of 2.0% octyl triazone with 5.0% zinc oxide to be particularly effective...

From Factors affecting the formulation of sunscreen products by John Woodruff, Creative Developments, UK
http://www.creative-developments.co....mulations.html

However, some people break out or have allergy reactions to chemical filters, and must stick to non-chemical sunscreens. The biggest problem with non-chemical sunscreens (ie. only zinc oxide and/or titanium dioxide) is that they are usually thick and white, pore-clogging, and simply not cosmetically pleasing. To solve that problem, a number of sunscreens with micronised minerals, in particular micronised zinc oxide, have appeared. Because the particles have been made really small (nanoparticles), the resulting product is more translucent and less pore-clogging. However, the effectiveness of such products may be compromised as a result (note 2 below), so those who are very photosensitive should be cautious when using such products. There is also the issue of photostability of such particles, and coated/encapsulated particles are preferred for better dispersion (ie. so they spread evenly and don't "bunch up") and photostability.

Micronised zinc oxides
In late 2004, Shiseido and BASF said they are to jointly develop new UV protection technology for cosmetic sun protection products. BASF patented Z-Cote, and we can expect to see this in Shiseido suncare products in the near future. Z-Cote comes in coated and uncoated forms, both of which are claimed to be photostable by BASF.
ZinClear is patented by Advanced Nanotechnology and is claimed to be more transparent and better dispersed than other forms of micronised zinc oxide. ZinClear-S is a siliconate coated version. Both are supposedly photostable, due to their patented manufacturing process.

Micronised titanium dioxides
Kemira patented UV-Titan, a series of micronised titanium dioxides that are surface-treated for better dispersion.
In early 2005, BASF introduced T-Lite microfine titanium dioxide, a transparent ultraviolet (UV) light filter manufactured by Sakai Chemical Industry Company of Japan. "BASF will market the T-Lite ingredients to cosmetic and sunscreen manufacturers globally, under an agreement with Sakai. T-Lite microfine titanium dioxide provides superior transparency and elegance and is highly compatible and stable in various oils." BASF had already patented Uvinul TiO2, a micronised titanium dioxide coated with trimethoxycaprylylsilane.

The good news is that, compared to the market a few years ago, micronised zinc oxide products are plentiful these days. Google and you'll find them, but most combine it with chemical filters. If you are determined to avoid chemical agents and want a translucent product, options are fewer. For optimum protection, pick a product with both titanium dioxide and zinc oxide. Here's a list of the ones I know (PM me if you know others):

* DDF Organic Sunblock SPF 30 (micronised zinc oxide and micronised titanium dioxide)
* Linda Sy ZincO Cream SPF 20, tinted and untinted (dimethicone-coated micronised zinc oxide)
* BirchTrees Daily Guard Sun Screen SPF 15 (micronised zinc oxide)
* SkinCeuticals Physical UV Defense SPF 30 (5% Z-Cote and 10% titanium dioxide)
* June Jacobs Micronized Sheer SPF30 (micronised zinc oxide and micronised titanium dioxide)
* Peter Thomas Roth Ultra-Lite Titanium Dioxide Sunblock SPF 30 (titanium dioxide 7.5%, zinc oxide 10.0%; either only the former or both micronised)
* Epicuren Discovery Zinc Oxide Sunscreen SPF 20 (micronised zinc oxide)
* Noevir Sun Defense Body SPF 30+ (micronised titanium dioxide 7.90%, zinc oxide 5.94%)
* Noevir Sun Defense Face SPF 15 (micronised titanium dioxide 5.53%)
* all Wet Dreams SPF 30+ sunscreens http://www.wetdreams.com.au/sunscreen.html (ZinClear)
* Megan Gale Invisible Zinc SPF30+, Invisible Zinc Daywear Moisturiser SPF30+, Tinted Lip & Cheek Balm SPF30+ (ZinClear)
* Blue Lizard Baby and Blue Lizard Sensitive, both SPF 30 (micronised zinc oxide and micronised titanium dioxide)
* Total Block C.O.T.Z. SPF 58 (micronised zinc oxide and micronised titanium dioxide)

1.Spectral protection, including UVA protection, from micronized physical agents varies according to the size of the micronized particles, with smaller particles providing more UVB and less UVA protection.
http://www.dermatology.org/skinthera...***#Sunscreens


Issues with micronised minerals

Physical sunscreen is made from nonorganic pigments like zinc oxide or titanium dioxide, which reflects or diffuses the radiation. In micronisized form (size: 10-100nm) the particles absorb the UV-radiation. The concentration of physical filters is not limited in Europe, as are the chemical filters. The extinction and effectiveness of titanium dioxide microparticles sized under 100 nm reaches in the UVB-wavelength, both substances mixed have a perfect broad spectrum effect. A good effect can be reached with different particle sizes of either substance.

The substances even in smallest particles do not penetrate into the skin and are chemically inert, so do not produce allergies, and work immediately after application.

Though, there are some negative aspects concerning physical filters. In pigmented form it whitens the skin and is not very effective against UV-radiation. In micro particles it tends to agglomerate and aggregate due to electrostatic effects, which means a enormous loss in efficacy. Therefore the micropigments have to be coated and kept in dispersion, which is still a great challenge for the cosmetic industry.'

From Sun Protection: Dermatological and Cosmetical Aspects
Werner Voss, M.D., Dermatest
http://www.dermatest.de/PB/Publikati...rotection.html

The use of microfine inorganic oxides as sunscreen materials continues to expand as the safety and photo-stability of these materials is confirmed. BASF has acquired the Z-Cote brand of zinc oxide dispersions to add to its portfolio of Uvinul organic and inorganic filters. Z-Cote is a hydrophilic white powder and Z-Cote HP-1 is zinc oxide treated with dimethicone to render it hydrophobic. Uvinul TiO2 is titanium dioxide coated with trimethoxycaprylylsilane to improve dispersion in oil and silicone-based systems. Kemira surface treats titanium dioxide to provide readily dispersed versions under the UV-Titan trade name. UV-Titan XIII is coated with alumina and is water-dispersible while X170 is surface treated with alumina and dimethicone, which renders it hydrophobic and suitable for oil and silicone based products. The average crystal size of these two materials is.14 nm, which assures their transparency. Grade X610 is a mixture of two crystal sizes and is recommended for skin care and cosmetic formulations.

Uniqema Solaveil continuously improves the quality and variety of its titanium dioxide and zinc oxide dispersions. Small distribution of particle size maximizes the absorption efficacy at the critical wavelengths while reducing the tendency to whitening that was once a problem with all microfine oxides. Latest grades of titanium dioxide include 50% dispersions in most of the commonly used esters and silicone compounds and aqueous dispersions with various preservative systems. When formulating with microfine oxides a mixture of titanium dioxide and zinc oxide assures a high SPF in association with good UVA protection. Using an oil-based dispersion of zinc oxide with an aqueous dispersion of titanium dioxide simplifies formulation by reducing the solids loading in any one phase.

From Sun Care SPC 2001 by Creative Developments, UK
http://www.creative-developments.co....are%202001.htm

Micronized titanium dioxide particles block UV rays not only by scattering and reflecting, but also by absorbing, which could generate free radicals that could be damaging. This feature of titanium dioxide has prompted some people to limit their use of it as well as chemical UV screens. It has also spurred manufacturers to find ways to reduce particle reactivity. Particles coated with silicone or a similar substance, have been show to be less reactive than uncoated particles.

If sunscreens stay in the epidermis, the effects of free radicals may not matter, since the epidermis is made of largely dead skin cells, but if they penetrate more deeply and are then excited by UV light, there may be damage to living tissue.

Recent studies have shown that micronized titanium dioxide particles, regardless of size or shape, stay within the outermost layers of the stratum corneum and do not penetrate to the deeper dermal layers but an earlier small scale study found that that levels of titanium dioxide in the epidermis and dermis of subjects who applied microfine titanium dioxide to their skin were higher than the levels of titanium dioxide found in controls. This finding has been questioned by many experts because there is no apparent method of transport for the particles. It may be an artifact of contaminated measurement devices.

The sunscreen solvent plays a role in how deeply a UV filter penetrates the skin, with oil in water emulsions (light lotions or gels) penetrating more deeply than water in oil emulsions (creams) or petrolatum (ointment) vehicles. Alcohol is a known penetration enhancer, and is often used in the lightest or gel base sunscreen formulations.

Microfine zinc oxide, which absorbs UV rays to a limited extent, also generates free radicals on UV exposure, but its reactivity is far lower than that of titanium dioxide and is essentially insignificant when the particles have a protective coating, usually silcone-based. Microfine zinc oxide’s superior protection compared to microfine titanium dioxide in UVA between 340 and 380 nm coupled with its lower potential for reactivity make it the first choice for many people. However, titanium dioxide is more efficient than zinc oxide at filtering UVB and short wave UVA, and a lower concentration of titanium dioxide than zinc oxide is needed to achieve a target SPF in a sunscreen formulation.

Despite their potential for reactivity and their possible ability to penetrate the skin, mineral sunscreens have been found to reduce UVB-induced lesions in DNA and UVA-induced strand breaks in human fibroblasts in a dose (SPF) dependent manner.

Free radicals generated deep in the epidermis by UV radiation are far more damaging than radicals generated in and among the dead cells in the stratum corneum where sunscreens reside. Radicals generated near the basal, germinative layer of the skin are much more likely to damage DNA in cells that can give rise to cancer. Instruments that are sensitive enough to measure DNA damage generated by sunscreens themselves may be of little significance because UVB striking unprotected skin typically generates oxygen radicals in a quantity that is several orders of magnitude greater than that of the sunscreen itself.'

From The Biochemistry of Beauty by Carol Demas & Barbara Kwiatkowska
http://tinyurl.com/4u3u4
(this cached page may expire any time)

[saresha]

The most popular sunscreen vehicles are creams and lotions. Two phase oil-in-water or water-in-oil emulsion systems allow for the widest variety in formulation. Most sunscreen ingredients are lipid-soluble and are incorporated into the oil phase of the emulsion. Higher SPF products may contain 20-40% sunscreen oils, accounting for the occlusive greasy feel of many of these products. Dry lotions, often presented as sport lotions, represent the formulator’s attempt to provide a less oily product.

Gels, sticks, and aerosols are other vehicles to deliver organic sunscreens. Water- or alcohol-based gels provide less greasy aesthetics, but they rely on the more limited number of water-soluble sunscreen ingredients and are less substantive with a greater potential for irritation. Sticks readily incorporate lipid-soluble sunscreens thickened with waxes and petrolatum and are heavier on application, but they are useful for protecting limited areas, such as the lips, the nose or around the eyes. Aerosols provide some convenience on application, but they may be difficult to apply evenly, which may result in a discontinuous film.

From http://www.emedicine.com/derm/topic510.htm

IOW, good sunscreen agents are only soluble in oil, thus making the product oil-free is impossible.

[sherrylouz]

Tip 1
Apply a broad-spectrum sunscreen with a UVA/UVB Sun Protection Factor (SPF) of 15 or higher.
Tip 2
Avoid the sun between 10 AM and 4 PM, when ultraviolet rays are strongest.
Tip 3
Apply sunscreen over skin 30 minutes before going outdoors. Reapply every two hours when outside, even on cloudy days.
Tip 4
Wear a wide-brimmed hat, sunglasses, and tightly woven clothing such as long-sleeved shirts and pants.
Tip 5
Apply sunscreen during sports, even in winter. Use a spray sunscreen to prevent hands from becoming greasy.
Tip 6
Remember to be extra careful about your protection near reflective surfaces—snow, ice, and water— because they bounce back up to 85 percent of the sun’s damaging rays.
Tip 7
Protect children: minimize sun exposure early by applying sunscreen daily to children six months or older. Most sun damage is done by the age of 18.
Tip 8
Avoid tanning beds. A self-tanner alone doesn’t protect. Use a self-tanner with an SPF for the look without the risks of sun bathing. Spray-ons work best.
Tip 9
Wear a moisturizing sunscreen on your face year-round, preferably with an SPF of 15 or higher. Choose a fragrance-free, vitamin-enriched lotion that won’t clog pores. If you think creamy sunscreens make you look greasy apply one with powder format like Maybelline’s whitestay uv
Tip 10
Make sun protection part of your daily routine. It’s one of the best long-term investments you’ll ever.


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