From the Guidelines
The photocatalytic effects of sunscreen are a concern, but the benefits of using sunscreen in preventing skin cancer and photoaging far outweigh the potential risks. When considering the photocatalytic effects of sunscreen, it's essential to understand that certain ingredients, such as titanium dioxide and zinc oxide nanoparticles, can absorb UV light and generate reactive oxygen species, potentially damaging skin cells and DNA 1. However, it's crucial to note that the U.S. Food and Drug Administration has determined that broad-spectrum sunscreens with a sun protection factor of 15 or greater, if used as directed, protect against UV A and UV B radiation and reduce the risk of skin cancer and early skin aging 1. Some key points to consider about photocatalytic effects of sunscreen include:
- The potential for mineral-based ingredients to act as photocatalysts when exposed to sunlight
- The importance of particle size, coating, and formulation in determining photocatalytic activity
- The role of antioxidants in neutralizing reactive species and minimizing photocatalytic effects
- The availability of "photostable" formulations that reduce the risk of photocatalytic damage To minimize photocatalytic effects, consumers can choose sunscreens with coated mineral ingredients or those containing additional antioxidants, while still benefiting from essential UV protection. Ultimately, the protective benefits of sunscreen against skin cancer and photoaging significantly outweigh the potential risks from photocatalytic effects, making sunscreen a crucial component of skin care and cancer prevention 1.
From the Research
Photocatalytic Effects of Sunscreen
- The photocatalytic effects of sunscreen are a concern, particularly with the use of titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles 2.
- These effects cannot be completely prevented by coating the particles, but silica-based coatings are most effective in reducing them 2.
- The photocatalytic effects of TiO2 are higher than those of ZnO, with anatase TiO2 having the highest effects 2.
- The use of mixtures of micro- and nanosized ZnO dispersions and nanosized TiO2 particles may improve the balance between UVA and UVB protection and reduce photocatalytic effects 2.
Mechanism of Action
- Titanium dioxide and zinc oxide provide UV protection primarily via absorption of UV radiation and not through significant reflection or scattering 3.
- The average range of reflection for zinc oxide and titanium dioxide throughout the UV range is only 4-5%, providing minimal UV protection via this mechanism 3.
- At wavelengths above the semiconductor band gap absorption energy levels, TiO2 and ZnO are predominantly reflectors of light and non-absorbing 3.
Safety and Efficacy
- The risk for humans from the use of nano-structured TiO2 or ZnO currently used in cosmetic preparations or sunscreens is considered negligible 4.
- Multiple studies have shown that under exaggerated test conditions, neither nano-structured TiO2 nor ZnO penetrates beyond the stratum corneum of skin 4.
- The distribution and persistence of these nano-structured metal oxides are the same compared to larger pigment-grade particles, demonstrating equivalence in the recognition and elimination of such material from the body 4.
- Sunscreens containing TiO2 and/or ZnO have been shown to provide effective protection against sunburn, photocarcinogenesis, photoaging, pigmentary disorders, and idiopathic photodermatoses 5.