Titanium dioxide (TiO2) is a naturally occurring mineral compound widely used in consumer products as a white pigment and as a physical ultraviolet (UV) filter. In applications like sunscreens and cosmetics, the compound sits on the surface to reflect and scatter light, protecting skin from solar radiation. Safety discussions surrounding TiO2 often center on the size of its particles, distinguishing between the ultrafine nano-sized form and the larger non-nano grade.
Defining Non-Nano Particle Size and Function
Non-nano titanium dioxide refers to particles that are generally larger than 100 nanometers (nm) in diameter. Pigment-grade TiO2, which is the non-nano form, typically has a median particle size ranging from 200 to 300 nm. This larger size prevents the material from appearing transparent and is what causes the visible white cast often associated with older mineral sunscreens.
The primary mechanism by which non-nano TiO2 provides sun protection is through physical light reflection and scattering. Its substantial size and high refractive index act like tiny mirrors, physically blocking UV radiation from reaching the skin. This mechanism contrasts with the nano form, which is transparent and relies more heavily on absorbing UV energy due to its increased surface area.
Safety Profile in Topical Applications
The safety of non-nano titanium dioxide when applied to the skin is well-established by regulatory bodies worldwide. Due to its comparatively large particle size, non-nano TiO2 cannot penetrate the stratum corneum, which is the outermost layer of the skin. Scientific consensus indicates that, even with the smaller nano-sized particles, there is no significant penetration into the viable skin cells or the bloodstream.
Studies confirm that non-nano particles remain on the skin’s surface, forming a protective barrier without causing systemic exposure or toxicity. The U.S. Food and Drug Administration (FDA) and the European Union’s Scientific Committee on Consumer Safety (SCCS) have both concluded that TiO2 is safe for use as a UV filter in cosmetics and sunscreens when applied to healthy, intact skin. This safety profile is why mineral sunscreens using non-nano TiO2 are often recommended for sensitive skin or for children.
Assessing Safety Through Other Routes of Exposure
While topical use is considered safe, the safety profile of titanium dioxide changes significantly when considering other routes of exposure, specifically ingestion and inhalation.
Ingestion
Concerns surrounding ingestion relate to titanium dioxide’s use as a food additive, known in Europe as E171, which provides whiteness and opacity to various products. E171 is a mixture of particles where up to 50% of the constituent particles may be in the nano size range. In 2021, the European Food Safety Authority (EFSA) concluded that TiO2 can no longer be considered safe as a food additive due to the inability to rule out a concern for genotoxicity. This conclusion was based on evidence that TiO2 particles, though poorly absorbed by the digestive tract, can accumulate in the body and potentially cause damage to cellular DNA.
Inhalation
Inhalation of titanium dioxide powder presents a distinct hazard, regardless of the initial particle size, as any dry powder can create respirable dust. The International Agency for Research on Cancer (IARC) classifies inhaled TiO2 dust as a Group 2B possible human carcinogen. This classification is based on animal studies that showed lung tumors after prolonged inhalation of high concentrations.
The risk is highest in occupational settings where workers handle large quantities of powdered TiO2, but it also applies to consumer products like loose cosmetic powders or spray sunscreens. These aerosolized products can generate respirable particles, which are defined as those 10 micrometers or less, capable of reaching the deep lung tissue. In the lungs, these particles can cause inflammation, which is the underlying mechanism for the carcinogenicity concern. Therefore, while non-nano TiO2 is highly safe on the skin, its powdered form carries a recognized inhalation risk.