Titanium dioxide in cosmetics: what are the risks?

What about dermal exposure and skin penetration of titanium dioxide?

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.

Are there risks associated with inhaling titanium dioxide?

It is well established that nano-TiO₂ are more toxic than the micrometric form. Indeed, nano-TiO₂ particles can be inhaled when present in spray or aerosol products, such as certain sprays, although their use in these formulations has been prohibited since 2009 by EU Cosmetics Regulation (EC) No. 1223/2009. Inhalation of these particles may cause respiratory irritation and pulmonary inflammation, which over time may lead to impaired lung function, fibrosis and cancer risk, depending on their nanometric properties (size, shape, crystallinity, etc.). The risks are mainly associated with occupational exposure or aerosol cosmetic products.

However, these cases are rare in domestic use, and prolonged or high-dose exposure appears more problematic. For short-term inhalation, a threshold of 3.5 mg/m³ is estimated for spray applications, and a threshold of 17 mg/m³ is suggested for repeated inhalations over an eight-hour working day. Studies show that inhalation concentrations up to 35 mg/m³ do not cause chronic pulmonary overload.

Risks of titanium dioxide ingestion?

In recent years, concerns have emerged over the use of titanium dioxide after its ban as a food additive (E171) in some countries. It is essential to distinguish its use in foods from its use in topical formulations, where exposure levels and contexts differ.

Studies available to date using models in vitro and in animals have reported that gastrointestinal absorption of titanium dioxide, whether nano or non-nano, after oral exposure is negligible or nonexistent. The amounts of TiO₂ used in these experimental studies exceed those to which people may be exposed through accidental ingestion, for example when using lip products such as lipsticks. Current data do not show clear evidence of carcinogenic or genotoxic activity associated with oral ingestion of titanium dioxide.

Distinguishing the exposure contexts assessed by different regulatory agencies is important. The CSSC assesses the risks of titanium dioxide in topical products not designed for ingestion, where any ingestion is accidental and involves negligible quantities. By contrast, the European Food Safety Authority (EFSA) assesses titanium dioxide as a food additive, where exposure levels are much higher due to deliberate consumption in foods.

To summarise, although uncertainties remain, current data do not indicate significant concern over accidental ingestion of titanium dioxide in cosmetics, given the low amounts involved and the absence of clear evidence of toxicity. However, further research is needed to clarify long-term effects and reassure consumers.

It is important to note that the nano-TiO₂ form presents a greater potential risk than the micrometre form, due to its increased penetration into tissues and cells.

Effects of titanium dioxide in pregnant or lactating women?

To date, there is no specific ban or warning on the use of skincare products containing titanium dioxide by pregnant or breastfeeding individuals, including lip products. Regulatory authorities consider the levels of titanium dioxide in these products safe for consumers, including in cases of accidental ingestion.

However, some experimental studies have examined the effects of titanium dioxide on pregnancy and postnatal development. For example, one study administered 100 mg/kg/day of nano-TiO₂ orally to pregnant rats during gestation. Although this dose exceeds human exposure from cosmetic use, where incidental ingestion is minimal, the results showed minor physiological disturbances in the mothers, such as altered antioxidant enzyme levels and metabolic markers. Titanium dioxide also accumulated in organs including the liver, brain, and placenta.

In the offspring, effects on postnatal development were observed, including variations in body weight, delays in sensorimotor maturation, and changes in motor reflexes. These observations suggest a potential effect on the central nervous system, although no major malformation or structural anomaly was detected in the foetuses.

It is crucial to note that these findings come from animal studies using doses exceeding those encountered in everyday life.

For example, accidental ingestion of titanium dioxide from lip products is minimal and represents only a tiny fraction of the dose tested in these studies. Moreover, human data on this topic are limited and show no conclusive evidence of risk for pregnant or breastfeeding individuals.