Hielscher describes why ultrasonication is critical in the preparation of sun protection cremes.
Every day, sun rays encounter and penetrate the skin.
If they are not absorbed by the atmosphere, the skin's own photoprotection is usually not sufficient to protect against ultraviolet radiation.
This can result in damage like sunburn, changes in DNA, cell death or cell abnormalties.
Sunscreen is of critical importance, and there are key differentiations between chemical and physical lotions.
Chemical screens include organic, aromatic compounds, which are capable of absorbing UV radiance.
Physical sunscreens consist of inorganic substances which are applied on the skin without penetrating into the skin layers.
To achieve medically effective sun protection against UV radiance, it is necessary to combine UVA and UVB filters with antioxidants, which reduce the number of free radicals.
For production of cosmetic sunscreens in the form of creams and lotions, mineral pigments such as titanium dioxide and zinc oxide are used.
Both types of organic pigments are proven to protect skin against damage resulting from ultraviolet rays.
Ultrasound is an appropriate and well-known tool for the preparation of nano-sized pigments by ultrasonic deagglomeration and grinding.
It is also used for ultrasonic dispersing and emulsifying.
This is of high importance for the production of the W/O or O/W emulsion, the basis of creams and lotions.
To avoid the undesirable whitening effect of TiO2 and ZnO that can occur using creams or lotions containing these organic ingredients, the use of very small pigments in micron- and nano-size is essential.
Ultrasonic deagglomeration and milling and grinding are proven methods for particle size reduction.
