Assessment of Whitening Effect

Whitening can be assessed either visually or instrumentally (by colorimetry). The quantities evaluated are the degree of whiteness and the tint. Special attention must be paid to the spectral distribution of the incident light in the UV and visible ranges, since this controls the fluorescent contribution of the brightener to the whiteness [171], 

Visual assessment is performed by comparison with references in diffuse daylight [172], White scales consisting of stages with well-defined whiteness values (e g., the cotton or plastic white scale) can be used [173], 

For instrumental evaluation spectrophotometers are preferred. The colorimetric values obtained depend on the instrument and its instantaneous state (chiefly the sample illumination conditions) and must be controlled by suitable methods [174], The influence of the instrument can be eliminated by conversion to the standard illumination D 65, representing daylight with a correlated color temperature of 6504 K [175]. The degree of whiteness and the tint values can then be calculated from these colorimetric data with appropriate formulas. A selection of currently used whiteness formulas can be found in [176,177], For recent attempts at standardizing the assessment methods for white objects, see [9,178-185], 

Both the toxicology and the ecotoxicology of commercial FWAs for cotton/paper have been extensively studied [7,19,186], 

As industrial chemicals, FWAs are regulated by national laws such as the Toxic Substance Control Act in the United States and the relevant classification, packaging, and labeling directives in the European Community. For specific applications such as food packaging, the national regulatory requirements must be complied with. 

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Ahn and Kim [10] used colorimetry to assess the whitening effect of biweekly 30% salicylic acid peels in Korean patients with acne and post-inflammatory pigmentation. After 3 months, there were significant improvements in colorimettic parameters, reflecting a reduction in hyperpigmentation. 

Safety is a primary consideration for tyrosinase inhibitors, especially when utilized in unregulated quantities on a regular basis. On the other hand, the use of the inhibitors is primary in the cosmetic industry due to their skin-whitening effects. Since a huge number of tyrosinase inhibitors have been developed, assessing the validation of these inhibitors in skin-whitening efficiency has become more important. Most inhibitors have rarely been incorporated in topically applied cosmetics, often due to a lack of parallel human clinical trials (Chang, 2009 Khan, 2007 Kim, 2005). 

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