What do you need to know about titanium dioxide?

Titanium dioxide is a natural metal found in minerals such as ilmenite and rutile. The production of titanium dioxide pigments began in the 1920s using ilmenite and sulphuric acid. First anatase pigments were produced. Rutile pigments followed in the 1940s, before chloride-route rutile pigments appeared in the late 1950s.

Titanium dioxide occurs in three forms: anatase (65–91% TiO2), rutile (92–96% TiO2) and brookite (>96% TiO2). Anatase is the most common form in industrial products, rutile is more stable and brookite is rare. It can also occur in an amorphous form. Titanium dioxide is mainly produced in two size ranges: micrometric (micro-TiO₂) between 250 and 400 nm and nanometric (nano-TiO₂) below 250 nm.

Micro-TiO₂ is used to provide whiteness and opacity in paints, personal care products, and plastics, accounting for 98 per cent of global output. In contrast, nano-TiO₂ is valued for its transparency and reactivity in UV filters and other products. While nano-TiO₂ has many useful applications, its small size raises safety concerns, as it can interact with biological tissues and the environment.

The most common industry method to produce titanium dioxide is the sulphate process. This method involves treating ilmenite ore with sulphuric acid at high temperature to produce titanium sulfate. The resulting titanium sulfate is purified and converted into titanium dioxide. The method is common due to low cost and raw material availability. It produces large volumes of titanium dioxide for applications such as paints, cosmetic products and food. However, it generates substantial by-products and is less environmentally friendly than newer methods.

There are other titanium dioxide production techniques: sol-gel, hydrothermal/solvothermal, co-precipitation, microemulsion, molten salt and aerosol synthesis. These methods control particle size, morphology and crystalline phase, and suit specific applications such as photocatalysts or industrial pigments. They see limited large-scale use due to high cost, energy demand and technical complexity. Aerosol synthesis requires temperatures of 1,000 °C to 1,500 °C.

The titanium dioxide is one of the most versatile and widely used nanomaterials in industry, with varied applications. In skincare, it functions as sunscreen filter and white pigment in sun care and colour products to provide protection and opacity. In textiles, it enhances UV resistance, thereby increasing the durability of materials exposed to sunlight. In paints and coatings, its UV-blocking ability and whiteness protect surfaces against photochemical degradation. In pharmaceuticals, it acts as an opacifier and stabiliser in formulations. It is also found in various household products, building materials, and fabrics for its protective and stabilising properties.

The titanium dioxide is well known for its sun-protecting properties. It acts as a physical sunscreen filter that absorbs UV rays across a wavelength range from about 290 nm to 390 nm, covering both UVA (320–400 nm) and UVB (290–320 nm). This helps prevent sunburn, slow skin ageing, and reduce the risk of skin cancer. At the same time, titanium dioxide acts as an antioxidant by neutralising free radicals through an electron transfer mechanism, which helps prevent signs of skin ageing.

It is also used to brighten and even out skin tone, as its opacifying and reflective properties help scatter visible light, giving skin a natural finish and temporarily camouflaging imperfections. Titanium dioxide is also used as a colourant in tinted products.

When combined with other ingredients, titanium dioxide can enhance the anti-inflammatory properties, helping to soothe skin and protect it from irritation caused by external factors such as pollution and stress. When combined with silver oxide nanoparticles encapsulated in gelatine, titanium dioxide can accelerate the regeneration of skin tissues. This combination has anti-inflammatory and antibacterial effects that promote more rapid wound healing.

In hair care, titanium dioxide is sometimes added to products for its opacifying properties and UV protection. Although it is used for its protective and cosmetic benefits, no scientific study has demonstrated a significant effect of titanium dioxide on hair growth. This issue remains unconfirmed and requires further research to assess any potential effects on hair growth.

The titanium dioxide has been used for decades in its micro-TiO₂ form in cosmetic, food, and industrial sectors. This form, with particles measuring between 250 and 400 nm, is considered safe for human health under normal use conditions. However, with the advent of nanotechnology, the nano-TiO₂ form, with particles smaller than 250 nm, has raised concerns due to its increased reactivity and potential to interact with biological tissues.

The nano-TiO₂ form, which appeared recently, raises questions due to its small size and increased reactivity. Nano-TiO₂ can access biological tissues, prompting detailed studies on their potential health effects. Here is a summary of the risks associated with each exposure route.

• Cutaneous risk of titanium dioxide.

  The nano-TiO₂ form raises concerns due to its potential to enter the bloodstream. Although a few studies have detected traces of nano-TiO₂ in urine, evidence indicates it does not pass through intact skin. Human skin has unique barrier properties that prevent nano-TiO₂ particles from reaching the dermis. Multiple studies show that particles under 100 nm do not traverse the skin. In rare cases where small amounts of nano-TiO₂ penetrate, no significant toxicity has been observed under specific conditions. Further research is needed to assess long-term effects, including on damaged skin.

• Oral risk associated with titanium dioxide.

  The titanium dioxide in nanometric form is now banned in food in all its forms due to growing concerns about its health effects. Upon ingestion, nano-TiO₂ may accumulate in organs such as the liver, spleen, kidneys, and lungs, where it can trigger toxic effects, including nephrotoxicity and liver injury. Although excreted via faeces, prolonged deposition in tissues may cause long-term effects whose mechanisms remain unclear.

  However, cosmetic products containing titanium dioxide, such as sunscreens and tinted formulations, contain much lower concentrations of titanium dioxide, and their application is topical on skin or near mucous membranes. The difference in concentration and mode of application reduces the risk of internal absorption. In cosmetic products, TiO₂ provides pigmentation and UV protection, not for food use.

• Risk of inhaling titanium dioxide.

  In industrial settings, inhalation of nano-TiO₂ may carry greater risk. Fine particles in anatase form pose higher hazards as they can cause respiratory issues. This is why the use of nano-TiO₂ in spray form is prohibited. It is crucial to implement adequate safety measures in workplaces handling titanium dioxide to minimise risk.

Nano‐TiO2 particles, due to their reactivity and persistence in aquatic environments, may pose a risk to ecosystems. In soil, they may reduce microbial diversity and disrupt ecological processes. Plant roots may absorb these particles, facilitating their spread in the environment. This may disturb photosynthesis and affect plant growth.

In aquatic environments, they accumulate in living organisms and disrupt the food chain, causing multiple toxic effects in phytoplankton and some fish. Their interaction with heavy metals and other toxic compounds increases environmental toxicity. This toxicity threatens animals, plants, and wildlife and underscores the need for research to limit contamination.

As for micro-TiO₂, although less reactive than their nano counterparts, their persistence in the environment raises concerns. They could accumulate in soils and aquatic sediments, affecting living organisms and ecological processes over the long term.

These impacts highlight the need to continue research to better understand the environmental effects of titanium dioxide, both in nano and micro forms, and to develop strategies to limit its contamination.

• Titanium dioxide pigments. Springer Science (1983).

• PRATSINIS S. E. Flame aerosol synthesis of ceramic powders. Progress in Energy and Combustion Science (1998).

• CHURAGULOV B. R. & al. Synthesis of ZrO2 and TiO2 nanocrystalline powders by hydrothermal process. Materials Science and Engineering (2003).

• GEOBALDO F. & al. Synthesis, characterization, and photocatalytic application of novel TiO2 nanoparticles. Chemical Engineering Journal (2010).

• ASCHBERGER K. & al. Nano-TiO₂--Feasibility and challenges for human health risk assessment based on open literature. Nanotoxicology (2011).

• HUANG Y.-J. & al. Effects of various physicochemical characteristics on the toxicities of ZnO and TiO nanoparticles toward human lung epithelial cells. Science of the Total Environment (2011).

• PARKIN I. P. & al. Enhanced photocatalytic and antibacterial ability of Cu-doped anatase TiO2 thin films: Theory and experiment. ACS Appl Mater Interfaces (2020).

• WU A. & al. Toxicity of TiO nanoparticles. In TiO2 Nanoparticles; John Wiley & Sons, Ltd (2020).

• CAVALLO D. & al. Assessment of the influence of crystalline form on cyto-genotoxic and inflammatory effects induced by TiO2 nanoparticles on human bronchial and alveolar cells. Nanomaterials (Basel) (2021).

• TOMSIC B. & al. Influence of titanium dioxide nanoparticles on human health and the environment. Nanomaterials (2021).

• KANG Y. S. & al. Synthesis of uniform size Rrutile TiO2 microrods by simple molten-salt method and its photoluminescence activity. Nanomaterials (2022).

• RACOVITA A. D. Titanium dioxide: Structure, impact and toxicity. International Journal of Environmental Research and Public Health (2022).

• SAYES C. M. & al. An updated review of industrially relevant titanium dioxide and its environmental health effects. Journal of Hazardous Materials Letters (2023).