The titanium dioxide is an essential ingredient in many skincare products for its photoprotective properties against UV radiation and role in powders and creams. One major concern is its interaction with the skin and its capacity to penetrate different skin layers.
Before examining the results of specific studies, it is important to remember that the structure of the skin acts as an effective natural barrier, limiting the absorption of many substances. This section explores various exposure pathways and evaluates potential safety implications for this ingredient.
Absorption of titanium dioxide through healthy skin.
The non-nanoscale titanium dioxide is used in skincare products due to its well-established safety: it stays on the skin surface and does not penetrate the living layers of the epidermis. However, the nano-TiO₂ form raises more concern because its size could enable deeper penetration into the skin.
The Scientific Committee on Consumer Safety (SCCS) reviewed more than twenty studies between 2013 and 2014 on the absorption of TiO₂ (nano-TiO₂ and non-nano) through the skin. The results show that, in all cases, TiO₂ remains on the skin surface, with minor penetration into the stratum corneum for nano-TiO₂, without evidence of penetration into the viable epidermis or dermis.
Other studies in vivo and in vitro on human skin have also suggested that nano-TiO₂ may penetrate deeper into the skin, especially when formulated in an oil dispersion. However, an oil-in-water emulsion, in which titanium dioxide is dispersed in the aqueous phase, prevents this penetration. Another study, conducted on minipig grafts, indicated deeper nano-TiO₂ penetration, although it was not significant, across intact and normal epidermis.
In addition, applying a cream to minipig skin for about one month showed no apparent adverse effects on the animal’s skin, such as irritation. Other studies have shown that nano-TiO₂ does not penetrate beyond the stratum corneum when combined with cetyl phosphate, manganese dioxide, and triethoxycaprylylsilane in cosmetic formulations. A 2016 review by theAustralian Therapeutic Goods Administration confirms that penetration is limited to the stratum corneum, although one study did note slight penetration after repeated application of sunscreen containing nano-TiO₂.
According to the CSSC, nano-TiO₂ and non-nano-TiO₂ in sunscreens pose no health risk when applied to the skin at concentrations up to 25%.
A potential penetration of titanium dioxide into the bloodstream?
A study of dermal penetration of TiO₂ used 12 minipigs. Researchers used non-nano and nano TiO₂ at 5% concentration in a sunscreen. These formulations and controls were applied to the skin of minipigs at 2 mg/cm², with four applications per day, five days per week, for four weeks. Skin, lymph nodes, and liver were sampled to analyse TiO₂ levels. Titanium dioxide levels in lymph nodes and liver of treated animals did not exceed those in control animals.
These preliminary data suggest that TiO₂ does not penetrate the bloodstream.
And what about the absorption of titanium dioxide through compromised skin?
The CSSC reviewed five studies on titanium dioxide penetration under compromised skin conditions (shaved, sunburned, psoriatic) in mice, pigs, and humans. These found that titanium dioxide, both micrometric and nanometric, did not penetrate compromised skin more deeply than healthy skin. Although nano-TiO₂ reached deeper layers of the stratum corneum in psoriatic skin, it did not enter living cells in either skin type. Further research confirmed limited penetration of nano-TiO₂ in intact or mildly damaged skin. One study of human skin exposed to UVB rays detected nano-TiO₂ in viable cells, but only in two volunteers using a single sunscreen.