UV absorbers are substances with the capacity to absorb UV light in the range between 100 and 400 nm and to convert it to a lower level of radiated energy, e.g. radiation in the form of fluorescence or heat. This radiation is not usually capable of causing damage to the product or to the skin.
The cosmetics producer must check for himself in each case which UV absorber is suitable for a particular colorant or active substance because their efficiency depends to a considerable extent on the basis formulation employed. The investigations described in the following section do, however, provide an indication as to which UV absorber is most suitable for which colorant.
It is always necessary to check the solubility of the UV absorber in the various formulations since this can be decisive for the amount to use. Furthermore, it should be noted that certain UV absorbers have a yellow coloration, which can influence the shade of the end product.
The use of many organic colorants in cosmetics is restricted owing to their instability to light. In most cases, this instability is caused by UV radiation and it manifests itself by fading of the color. Colorants that exhibit maxima in the UV range of their absorption spectrum are characterized by an extremely high instability to UV light.
In many cases, appropriate protection can be achieved by using UV absorbers. These can either be incorporated directly in the cosmetic formulation or in the transparent packaging material (plastic).
Since cosmetic formulations contain only very small amounts of colorants, concentrations of UV absorbers as low as 0.01 - 0.5 % are sufficient. These concentrations are not subject to EC directives when the absorbers are used for product protection, i.e. even UV absorbers that are not included in the positive list can be used.
There is thus a wide selection of UV absorbers that can be considered. Since the fading of colorants is frequently due to UV-A radiation, i.e. radiation of wavelengths longer than 320 nm, substituted benzophenones are being increasingly favored for product protection. The benzophenones are broad-range absorbers; in other words, they can absorb in both the UV-A and in the UV-B range.
Which substances can be protected?
All substances that are sensitive to light. These are mainly the colorants, active substances, and perfumery oils present. in the case of the colorants, any instability to light is readily apparent to the end-user by the fading that occurs, whereas the decomposition of the other substances cannot be determined without conducting a complicated analysis.
When is it necessary to add a UV absorber for product protection?
The addition of UV absorbers is only necessary when the product is likely to be exposed to UV light - as is the case when it is marketed in a transparent pack. There is no need for UV absorbers in products that are sold in aerosol cans, nontransparent jars, or tubes. If cosmetics that have been packed in this way should, nevertheless, show a change in shade, the reason is frequently to be found in an incompatibility with other ingredients.