Titanium dioxide, an ingredient with numerous aspects.

Role No. 1: Titanium dioxide is recognised as an effective mineral sunscreen.

Besides zinc oxide, titanium dioxide is the other physical sunscreen filter available on the market. When incorporated into sun creams, it works by creating a physical barrier on the skin's surface that absorbs and disperses ultraviolet rays (290 to 400 nm), helping to prevent damage caused by these harmful rays. This mineral is often favoured for its safety and chemical stability, particularly for sensitive skin, as it slightly penetrates the skin but mainly remains in the upper layer of the epidermis (horny layer), thus providing immediate and effective UV protection while minimising the risks of deep penetration.

An in-depth comparative study has confirmed its superiority over zinc oxide, particularly due to advanced technologies such as micronisation and particle coating (alumina, fatty acids). These innovations significantly increase its photoprotective efficiency, allowing it to reach a sun protection factor (SPF) of up to 38, far surpassing zinc oxide which achieves a maximum SPF of 10. Furthermore, these processes enhance its cosmetic application by eliminating the "white mask" effect. This study highlights the importance of favouring formulations based on scientifically validated sun filters, such as TiO₂.

However, substances such as talc, historically used for their supposed photoprotective effects, have proven to be ineffective, with a negligible SPF of around 1.

Role No. 2: Titanium dioxide, a key ingredient for opacity and colour products.

TiO₂ is a key component in many products, such as foundations, loose powders, and complexion correctors, due to its unique physical properties. As an opacifier, it is capable of creating a denser and more uniform texture, which allows for natural coverage while minimising imperfections.

Thanks to its ability to scatter light, TiO₂ distributes light evenly across the skin's surface, reducing the appearance of irregularities, pores, and fine lines. This scattering phenomenon creates a smoother and more uniform complexion. In addition to its opacifying role, TiO₂ is used in tinted products to enhance the skin's texture, while providing discreet coverage and a flawless finish.

Role No. 3: Titanium dioxide, a colouring agent as a white pigment.

TiO₂ is a highly valued ingredient for its white colour and its ability to enhance the finish of cosmetic products. Under the name CI 77891, it is widely used in the industry as a white pigment, providing opacity and shine.

Role No. 4: Titanium dioxide for its mattifying effect on oily skin?

TiO₂ is widely used in products designed for oily and combination skin due to its ability to absorb and disperse sebum. By adhering to the skin's surface, it captures and disperses sebum produced by the sebaceous glands due to its microporous texture and its absorption capacity, which reduces shine and provides a matte finish2,3,8. By absorbing and dispersing excess sebum on the skin's surface, TiO₂ not only helps to maintain an even complexion, but also extends the wear of skincare products, making it a key ingredient for care targeting skin prone to excess shine.

Role No. 5: Does titanium dioxide have an anti-inflammatory effect?

TiO₂ is reported to have anti-inflammatory properties by effectively neutralising reactive oxygen species (ROS), which can reduce inflammation and tissue damage. When ROS are produced in excess, they can cause oxidative stress. A study conducted on various types of cells, including skin fibroblasts, evaluated the anti-inflammatory activity of TiO₂ nanoparticles synthesised from caffeic acid, using the inhibition of bovine serum albumin (BSA) denaturation as an analysis method.

The denaturation of proteins and membrane lysis lead to the formation of auto-antigens in the human body. These auto-antigens are a major cause of inflammation and inflammatory diseases, such as asthma, rheumatoid arthritis, chronic gastroduodenal ulcer, tuberculosis, periodontitis, and Crohn's disease. To reduce the production of auto-antigens, it is crucial to control the percentage of protein denaturation and membrane lysis. The method of denaturing egg albumin proteins (BSA) is a cost-effective alternative for testing the anti-inflammatory activity of any sample. The results showed that TiO₂ would significantly inhibit the denaturation of BSA with rates of 70% and 85.7%, respectively at 31.25 and 500 µg/mL, which is comparable to the effect of diclofenac sodium, a standard anti-inflammatory drug.

Another study also confirmed the anti-inflammatory effect of TiO₂ synthesised from Gymnema sylvestre and Panicum sumatrense, showing an inhibition of protein denaturation ranging from 82.80% to 93.52% depending on the concentrations used. These data suggest that TiO₂ may have a promising anti-inflammatory potential, making it suitable for biomedical applications, particularly in the management of oxidative stress-related inflammatory processes.

Role No. 6: Titanium dioxide for its antioxidant effect?

In a study, TiO₂ nanoparticles were synthesised from kola nut extracts and demonstrated significant antioxidant activity. The results showed that these nanoparticles primarily function through electron transfer, enabling the trapping of free radicals such as DPPH (2,2-diphenyl-1-picrylhydrazyl), a commonly used indicator to measure antioxidant activity, with a trapping rate reaching 62.06% at a concentration of 80 µg/mL. Furthermore, the TiO₂ nanoparticles also exhibited a strong ability to neutralise hydrogen peroxide with trapping rates ranging between 78.45% and 99.23%.

Another study focused on TiO₂ nanoparticles synthesised from fruit peels, such as plum and kiwi, and revealed that their antioxidant activity increased proportionally with concentration. For instance, nanoparticles derived from plum peels achieved a DPPH radical trapping rate of 79%. These results suggest that TiO₂ nanoparticles, particularly those synthesised from natural sources, possess a significant efficacy against oxidative stress, thus opening promising prospects.

Role No. 7: Titanium Dioxide, an antimicrobial and antifungal agent?

According to the PubMed database, the antimicrobial properties of titanium dioxide nanoparticles (NP-TiO₂) have been described in over 1,000 articles since 2000, with a notable increase in publications dedicated to medical applications and the antimicrobial activity of TiO₂ nanoparticles, rising from 4% to 39% of the total number of publications between 2005 and 2023. Concurrently, the proportion of publications including the keywords "antibacterial" or "antifungal" has increased from 2% to 18%.

A recent study explores the antimicrobial potential of TiO₂ nanoparticles against multi-drug resistant (MDR) strains of Pseudomonas aeruginosa, a major nosocomial pathogen responsible for infections that are difficult to treat with conventional antibiotics. The researchers used commercial Degussa-P25 TiO₂ nanoparticles, characterised by an average size of 25 nm and a mixed rutile/anatase phase, to assess their antimicrobial effectiveness in combination with third-generation cephalosporin antibiotics, specifically Ceftazidime (CEZ) and Cefotaxime (CEF).

The strains of P. aeruginosa were isolated from pus, sputum, the trachea, and bronchoalveolar lavages, and their resistance to antibiotics was confirmed by sensitivity tests showing resistance to several commonly used antibiotics. The TiO₂ nanoparticles were exposed to UV light to activate their photocatalytic properties, generating ROS such as hydroxyl radicals (OH⁻) and superoxide ions (O₂⁻), known for their ability to lyse bacterial cell walls.

The results showed that TiO₂ nanoparticles exposed to UV light for an hour exhibited significant anti-microbial activity at concentrations higher than 350 µg/mL, with a minimum inhibitory concentration (MIC) established at 350 µg/mL. In combination with Ceftazidime, the TiO₂ nanoparticles demonstrated a synergistic effect, significantly enhancing the anti-microbial activity, while no similar effect was observed with Cefotaxime. This study suggests that TiO₂ nanoparticles, particularly when activated by UV light, could be a promising alternative for combating infections caused by multi-resistant strains of P. aeruginosa, thus offering a new approach to overcome antibiotic resistance.

Furthermore, studies have shown that NP-TiO₂ can also act on fungi. For instance, IRSHAD & al. observed that TiO₂ nanoparticles inhibit the growth of the fungus Ustilago tritici at concentrations of 25, 50, and 75 µg/mL. These findings confirm that NP-TiO₂ exhibit a significant antimicrobial and antifungal potential, offering a possible alternative to conventional treatments for combating skin infections.

Role No. 8: Is titanium dioxide involved in skin regeneration?

A study conducted by ELDEBANY & al. investigates the effectiveness of TiO₂ nanoparticles, encapsulated in gelatine (GLT-TiO₂), in the regeneration of skin tissues, particularly for the treatment of second-degree burns. The results show that second-degree burns promote a rapid healing. Compared to an untreated control group and a group treated only with gelatine, the GLT-TiO₂ demonstrated a significant reduction in wound area, accelerated re-epithelialisation, a decrease in oedema, and improved vascularisation.

Furthermore, immunohistochemical analysis revealed a higher expression of tissue regeneration markers, such as TGF-β1 and α-SMA, in the groups treated with GLT-TiO₂, particularly during the initial weeks of treatment. These findings suggest that TiO₂, due to its antimicrobial and hydrophilic properties, could play a key role in preserving skin moisture and stimulating cell growth, making it a promising candidate for burn treatment and skin regeneration. This study paves the way for further research to better understand the underlying mechanisms of TiO₂'s action in wound healing.