Carry out a quick search through beauty & cosmetic blogs & the number one complaint you will find associated with sunscreens is the white cast to the skin it leaves behind after application, especially to the face. They go on to mention the difference between physical & mineral UV filters & a basic explanation as to the reason behind the whitening effect.

Saying to consumers with no real scientific knowledge, especially those more appearance than safety conscious, that the whitening is due to physical UV filters, automatically makes the consumer shy away from products containing them. Few blogs actually explain the real scientific benefits of using physical sunscreens as opposed to chemical sunscreens.

Some even recommend chemical to physical options even though science & the cosmetic industry are more & more being forced to face the limitations & problems associated with chemical sunscreens. There was even one blog that when recommending using physical sunscreens said to look for nano on the labels to ensure a smoother application.

CHEMICAL Vs PHYSICAL SUNSCREENS

So, what is the difference between chemical & physical sunscreens? Chemical sunscreens use chemical UV filters that penetrate the epidermis & dermis of the skin & then absorb & dissipate UV rays from the sun. Physical sunscreens contain active ingredients that form a physical barrier on the surface of the skin that deflect & scatter UV rays.

Physical sunscreens are also known as mineral sunscreens because their active ingredients are mineral UV filters. There are two minerals types that are used in sunscreens currently, Zinc Oxide (ZnO) & Titanium Dioxide (TiO2).

There are several problems with chemical sunscreens which are coming to the surface as of late. The chemical UV filter additives in the sunscreens have been shown to be harmful to the environment & have an impact on human reproductive health. Hawaii has recently passed a bill that will ban certain chemical sunscreens, in order to protect their marine ecosystems. Several other regions are also looking into ways to reduce the use of chemical sunscreens consumers physical barrier sunscreens that are made with mineral active ingredients are much eco-friendlier.

Chemical sunscreens are also being criticised due to their narrow spectrum of UV protection. No single chemical UV filter can protect against both UVA & UVB rays from the sun. Most can only protect against UVB, when UVA radiation is arguably more harmful. Mineral filters in physical sunscreens can offer broad-spectrum protection, however, only ZnO can offer extensive & equal protection against both UVA & UVB rays. As a globally approved natural mineral ingredient, ZnO, is largely considered the most effective broad-spectrum UV filter.

Due to the various chemicals that formulate the chemical sunscreens, there are also much higher instances of allergic reactions & skin irritations in consumers using them compared to those using physical sunscreens. Chemical UV filters also have low photostability, so they degrade or destabilise much quicker when exposed to sunlight as opposed to mineral filers.

ZnO FORMS CURRENTLY USED IN SUNSCREENS

That classic image of the lifeguard walking the beach with a thick white paste, ZnO in its cruder form, on their nose is now a thing of the past. The ZnO found in sunscreen products nowadays comes in two conventional forms, of micron or nano particle size. While, micron ZnO is still not the most transparent UV filter available it still isn’t quite as thick as the ZnO sunblocks of the past. Particle size in the micron ZnO is larger, in the range of 2 to 10 µm. In the nano form, the ZnO particles are smaller, ranging from 10 to 40 nm.

Lifeguard with a layer of ZnO on his nose for protection from the sun’s UV rays

Comparison of the ZnO particle sizes in micron & nano ZnO formulations

Each of the two particle sizes, micron or nano has its own benefits & limitations. Micron ZnO is considered by some formulators to have better health & safety features than nano ZnO.

However, it is less effective as a sunscreen & less visually & aesthetically pleasing. Sunscreens with micron ZnO as the UV filter are the ones most associated with white cast.

However, the large particle size of micron ZnO is why it is considered the safer option from the two conventional ZnO formulations. The big concern with nanoparticles in general is also true for nano ZnO.

The small particles can penetrate through the skin of humans & accumulate in the roots of plants making nano ZnO possibly highly toxic to humans & phytotoxic.

Nano ZnO is more commonly used by formulators, as it is considered a much more effective sunscreen. Its higher efficacy is due to its ability to provide a higher protection to UV rays per percentage mass & cover a higher surface area per percentage mass compared to micron ZnO.

Nano ZnO’s high level of transparency also produces a more visually & aesthetically pleasing sunscreen.

These beneficial features however are dependent on the ZnO particles not agglomerating, which is a problem for nano ZnO, as it exhibits very high levels of uncontrolled agglomeration.

Micron ZnO also exhibits high levels of uncontrolled agglomeration.

NOVEL MicNo-ZnO; A SAFE, EFFECTIVE & NON-WHITENING UV FILTER

Entekno Materials have developed a novel mineral-based UV filter called MicNo-ZnO, that combines the benefits of both micron & nano ZnO. Using patented MicNo particle technology, Entekno were able to produce tailored, platelet shaped, micron sized particles composed of nano ZnO primary particles. MicNo-ZnO acts like micron ZnO over the skin, since it doesn’t penetrate through the skin, but still offers the transparent protection of nano ZnO.

Structure & primary particles of MicNo ZnO

MicNo has been shown through research to present much less cytotoxicity, genotoxicity & phototoxicity making it more biocompatible & safer when compared to commercial nano ZnO, similar to that of micron ZnO. This is due to the particles in MicNo being in the micron size range, so they are not able to penetrate the skin & enter plant roots easily, as opposed to the smaller nano particles. However, since the primary ZnO particles are nano ZnO, MicNo is still able to maintain the beneficial properties of nano ZnO.

ATTRIBUTE MICRON NANO MicNo®
UV Protection per mass Low High Very High
Transparency (unless they are aglomerated) No Very High High
Surface cover per mass Low High Very High
High energy visible light / Blue light protection High Low High
Level of toxicity Low Very High Low
Uncontrolled agglomeration High Very High Low
Level of phototoxicity Low Very High Low
Broad spectrum antibacterial activity Yes Yes Yes

Table exhibiting the main attributes of micron, nano & MicNo ZnO particles

MicNo provides a higher sun protection factor (SPF), which is the measure of protection from UVB rays, when used at the same concentration as nano ZnO. MicNo offers a much higher protection from UV rays per percentage mass than both nano & micron ZnO. It has also been proven to have a much higher absorbance of rays within the UV wavelength, especially in the UVA range, & a higher visible light transparency than commercial nano ZnO.

MicNo’s novel hexagonal shape can cover approximately 70% more surface area than the same amount of nano ZnO, assuming no agglomeration takes place. While uncontrolled agglomeration is a problem with commercially available versions of ZnO in both micron & nano formulations, MicNo has a low level of uncontrolled agglomeration. Thus, less MicNo is required in sunscreens to achieve the same sun protection as with nano & micron ZnO.

Distribution & surface coverage of 80 particles of nano ZnO compared to MicNo

Other benefits of MicNo include its antimicrobial properties, which are comparable to micron & nano ZnO. MicNo has exhibited broad spectrum antibacterial activity against a range of micro-organisms & fungi. It also offers high protection to high energy visible light & blue light.

MicNo can achieve a high transparency percentage at 440 nm wavelength, comparable to that of commercial transparent nano ZnO currently on the market. This high transparency means that the white cast effect is reduced.

Comparison of transparency (%) of MicNo & two other commercial transparent nano ZnO particles at 440nm wavelength

MicNo has a nano-porous structure that naturally creates a more ivory/beige colour as opposed to the milk white colour that is currently associated with ZnO sunscreens. This occurs due to a phenomenon called structural colouration, which is the production of colour when microscopically structured surfaces are fine enough to be able to interfere with visible light. Due to MicNo’s unique morphology it is also possible that products containing it may produce an attractive shimmer effect. Pearlescent pigments may produce attractive shimmers simply through the refraction of light.

The nano-porous structure of MicNo (right) causes a less milky white colour & creates a shimmer effect like on the butterfly wings (left)

MicNo is a novel & innovative particle that exhibits the safety of micron & the power of nano. With its unique design the MicNo particle can harness the benefits & overcome the problems associated with the conventional micron & nano ZnO forms currently used in sunscreens. Its novel design means that MicNo can not only offer an even better protection against the sun’s UV rays than conventional nano ZnO, while still maintaining the safety of micron ZnO, but it can also go a long way towards making physical sunscreens much more aesthetically & visually pleasing.

In a consumer driven beauty industry, the MicNo UV filter additive could provide you with the competitive edge required to stand out with a safe, effective & non-whitening sunscreen product.

For further information please contact,

Gürol Özhan Demirel
T: +90 222 320 36 63
M: +90 554 778 91 45
E: GurolDemirel@EnteknoMaterials.com