Are there any dangers associated with the use of zinc oxide in cosmetics?

Thezinc oxide (ZnO) refers to a chemical ingredient that combines a zinc atom with an oxygen atom. It is obtained by oxidising metallic zinc vapour, and this at high temperatures. The chemical reaction is written as follows:

2 Zn(solid) + O2 (gaseous) → 2 ZnO(solid)

This results in, on one hand, hexagonal and colourless crystals, and on the other hand, loose white powder due to the refraction of light in the small crystals. ZnO can also be obtained by incinerating zinc hydroxide, zinc nitrate, or zinc carbonate according to the following reaction:

Zn (OH)2 (solid) → ZnO(solid) + H2O(liquid)

Zinc oxide is primarily aUV protective filter. It is used in sun creams, acting as a shield on the skin's surface. Indeed, it iseffective in blocking and deflecting UVA and UVB rays, thus protecting the skin from the harmful effects of the sun.

For your information : Zinc oxide is also used as a colourant, you can find it on INCI lists under the nameCI 77947. It can also be used as an antibacterial agent, sanitiser and purifier for blemished skin and oily scalps, whether or not they have oily dandruff.

The controversy today revolves around the size of zinc oxide particles. Indeed, this matte white pigment comes in two dimensions.

• The Microparticles

  Typically used in deodorants for their antibacterial properties and in complexion makeup for their mattifying effect, zinc oxide microparticles are on the scale of a micrometre, as their name suggests. They are white and remain visible on the skin upon application.

• The nanoparticles

  Formulators use zinc oxide in the form of nanoparticles due to the final texture of the skincare product. These smaller particles make the product less pasty, more fluid, and easier to apply. The integration of nanoparticles as UV filters in sun care products is a recent development, following a directive from the European Union in April 2016. The health risks are as follows:potential percutaneous penetration, suspected reproductive toxicity, suspected genotoxicity, suspected carcinogenicity. For this reason, particularly in Europe, aerosols, sprays or powders containing zinc oxide nanoparticles are banned due to the risks of inhalation. Despite this, this UV filter remains bio-compatible according to the COSMOS standard.

At Typology, we apply the precautionary principle and exclude nanoparticles from our formulas. Our SPF30 face sunscreen with aloe vera contains non-nanometric zinc oxide.

However, it is important to clarify that whether zinc oxide is nano or not, exposure to high concentrations of this mineral compound can potentially cause a respiratory tract inflammation as well as pulmonary issues. For this reason, the European regulation has banned the presence of zinc oxide (nano or not) in spray formulas since 24th February 2018. Furthermore, zinc oxide is listed in Annex VI of the European regulation governing UV filters. Whether it is nanometric or not, its maximum permitted concentration as a UV filter is 25%.

As previously mentioned, zinc oxide can be used as a colourant (CI 77947) in accordance with Annex III of European Regulation No. 1223/2009. However, this usage is limited to a maximum rate of 5 % for body lotions and creams and up to 25 % for powders due to the toxicity of this trace element. Direct contact with nasal, ocular and vaginal mucous membranes is not recommended.