Titanium Dioxide in Cosmetics: Where Do We Stand?

According to the European database of cosmetic ingredients (Cosing), within a cosmetic formula, titanium dioxide can serve multiple functions.

• Cosmetic Colourant (White) : It is used to colour the product in question or to provide a hue to the skin. It is often found in tinted formulas such as foundations, primers, bb creams...

• Opacifier :it reduces the transparency or translucency of a formula to give it a mattifying appearance.

• UV Absorber : It protects the cosmetic formula from the effects of UV light, thus allowing the skincare product in question to last longer over time.

• UV Filter : this refers to a mineral filter capable of reflecting the raysUVwhich then cannot penetrate the epidermis and the dermis. Its mode of action is often compared to a mirror.

Note: Titanium dioxide is present in nanometric form only in sunscreens. This small particle size helps to avoid the white "snowman" effect upon application and ensures good UV protection as the product spreads more easily. When titanium dioxide is used for its opacifying character or as a colourant, it is instead preferable for the particles to be of a larger size (micrometric).

The issue with TiO2 in cosmetic formulas is primarily related to its inhalation , which leads to exposure of the lungs. In 2006, the International Agency for Research on Cancer (IARC) classified titanium dioxide in the group of substances "possibly carcinogenic to humans" (group 2B) when inhaled, regardless of the particle size (nano or not). This warning followed a study showing an increase in the number of lung cancers in animals after exposure to the white powder of titanium dioxide. However, it should be noted that this risk is associated with the inhalation of large quantities of titanium dioxide powder, particularly in the professional environment. The concentrations used in cosmetics are much lower and TiO2 is not harmful to health, except perhaps when it is formulated in aerosols. In 2016, ANSES (French Agency for Food, Environmental and Occupational Health & Safety) submitted a proposal to the ECHA (European Chemicals Agency) for the classification of titanium dioxide as a carcinogenic substance by inhalation (re-evaluation in category 1B).

Do nanoparticles penetrate the skin barrier? On this matter, studies contradict each other. A 2015 study showed that skin damaged by sunburn or atopic skin allows TiO2 nanoparticles to penetrate more easily, as the skin barrier protecting the body from the environment is weakened. The nanoparticles can then accumulate in the dermis and be more or less toxic. This same study defines the skin penetration of nanoparticles (NPs) as follows:

• NPs ⩽ 4 nm can penetrate and permeate intact skin;

• Nanoparticles ranging in size from 4 to 20 nm have the potential to penetrate both intact and damaged skin;

• Nanoparticles ranging in size from 21 to 45 nm can penetrate and permeate only damaged skin;

• NPs of size > 45 nm are in no way able to penetrate the skin barrier.

Conversely, studies conducted under the European research programme NANODERM have shown that nano TiO2 and zinc oxide do not penetrate the skin barrier, even in cases of superficial skin damage.

Today, research is still ongoing regarding their potential deleterious effects on the brain and their ability to form harmful oxidants for the skin under the effect of the sun's UV rays.

Thus, TiO2 primarily raises questions when it is inhaled and/or used in the form of nanoparticles.

Currently, in the absence of alternatives, titanium dioxide and zinc oxide are the only UV filters authorised in organic products, even in nanometric size. The SCCS (Scientific Committee on Consumer Safety) approved the use of titanium dioxide in nanoparticle form in sun creams as early as 2014, in concentrations less than 25%. However, this nanoparticle compound is banned in spray products. The EC regulation 2016/1143 of July 2016 has permitted the use of Titanium Dioxide in this form in cosmetics.

Nevertheless,in this context, the European Cosmetic Regulation n°1223/2009 has introduced a framework for nanomaterials, obliging manufacturers to be transparent.

Since the 11th of July 2013, when a nanomaterial is used in a cosmetic product, the packaging of this product includes in the list of ingredients thenotation [nano] following the name of the ingredient.

Thus, the consumer is free to choose whether or not to use a cosmetic containing nanoparticles. Another innovation introduced by the Regulation: all raw materials in the form of nanoparticles must be reported to the European Commission six months before the market launch of formulas containing them.

Note: In conventional cosmetics, TiO2 nanoparticles are permitted in all products.In organic cosmetics, nanoparticles are only permitted in sun care products.

Research on the ecotoxicity of TiO2 nanoparticles is relatively scarce compared to other nanomaterials, but initial findings urge caution, particularly due to their harmful impact on phytoplankton, an organism at the base of the marine food chain. They could also be partly responsible for coral bleaching.

• CROSERA M. & al. Nanoparticles skin absorption: New aspects for a safety profile evaluation. Regulatory Toxicology and Pharmacology. (2015).

• ZHONGHUA C. et al. TiO2 nanoparticles in the marine environment : Physical effects responsible for the toxicity on algae. Phaeodactylum tricornutum. Science of the Total Environment (2016).