Personal care  and cosmetic products are ubiquitous in our daily lives. Most of us wouldn’t readily go out to meet our peers without first practicing a bit of hygiene, which is why these products are so widely used. Personal care products and cosmetics are mainly applied externally (e.g., on hair, skin, and nails) as well as orally (e.g., on teeth, gums, and tongue) either for hygienic purposes, to modify appearance, or for general body maintenance. Some of the many examples of these items used on a regular basis include soaps, lotions, nail polish, concealer, hair dye, fragrances, ultraviolet (UV) absorbers, and antioxidants.

Personal care products are typically used for hygienic purposes and are rinsed away immediately after being used (e.g., toothpaste or soap), though some are meant to leave on the body, like sunscreen or hand sanitizer. In contrast, cosmetics are normally worn on the skin, minimally for a few hours (e.g., lotion, makeup, antiperspirant/deodorant, and other fragrances). Due to their wide use globally, these kinds of products are released in large quantities to the environment after washing or rinsing them off, which can lead to serious harm for other organisms.

Figure 1 shows the value of the global the personal care and cosmetics market for the top five leading countries as of 2020 [1]. This sector is expected to continue growing for the foreseeable future.

Importance of quality control

Considering the prevalence of these kinds of items in our everyday life, the amount of time they spend on our skin—the largest organ of the body, and the effect they can have on the environment after use, proper quality control (QC) of personal care and cosmetic products is extremely important.

Near-infrared (NIR) spectroscopy is an analytical method that is particularly suited for making QC of these end products more efficient and cost-effective. In the remainder of this article, a short overview on NIRS is presented, followed by some applications suitable for this industry. This overview concludes with some examples about how personal care and cosmetics producers can benefit  using NIRS in the laboratory.

NIRS technology: a short overview

The interaction between light and matter is a well-known process. Light used in spectroscopic methods is typically not described by the applied energy, but in many cases by wavelength or wavenumbers.

A NIR spectrometer (such as the Metrohm DS2500 Liquid Analyzer or DS2500 Solid Analyzer) measures this interaction to generate spectra as displayed in Figure 2. NIRS is especially sensitive to the presence of certain functional groups (e.g., CH, NH, OH, and SH). Therefore, NIR spectroscopy is an ideal method to quantify chemical parameters like water content (moisture), alcohol content, iodine value, total fatty matter, and active ingredients. Furthermore, the light-matter interaction is also dependent upon the matrix of the sample itself. This allows the detection of physical and rheological parameters such as density and viscosity.

Metrohm DS2500 Liquid Analyzer

Metrohm DS2500 Solid Analyzer

All this information is contained in a single spectrum, making this method suitable for quick multiparameter analysis.

The measuring mode is dependent on the sample type. The transmission mode is generally an appropriate procedure for analyzing liquids. During transmission (Figure 3b), the NIR light travels through the sample while being absorbed. Any unabsorbed NIR light reflects to the detector.

The transflection mode is generally an appropriate procedure for analyzing creams. For transflection (Figure 4b), the NIR light passes through the sample, then reflected by the diffuse reflector travels again through the sample while being absorbed. Unabsorbed NIR light is then detected at the end of the analysis.

The diffuse reflection mode is generally an appropriate procedure for analyzing solid samples like detergents. For diffuse reflection (Figure 5b), the NIR light illuminates the sample, and any unabsorbed NIR light reflects to the detector.

The procedure to obtain the spectra as shown in Figure 2 already highlights two major advantages of NIR spectroscopy: simplicity regarding sample measurement and speed:

• Fast technique with results in less than a minute.
• No sample preparation required – measure sample as is.
• Low cost per sample – no chemicals or solvents needed.
• Environmentally friendly technique – no waste generated.
• Non-destructive – precious samples can be reused after analysis.
• Easy to operate – inexperienced users are immediately successful.

For more detailed information about NIRS as a secondary technique, please read our previous blog posts.

Benefits of NIRS: Part 1

Benefits of NIRS: Part 2

Benefits of NIRS: Part 3

Benefits of NIRS: Part 4

Regulations for personal care and cosmetic products

In general, regulations for personal care and cosmetic products are not as strict as those for pharmaceuticals, but there are certain similar trends. NIRS is a technique that is quite suitable in such regulated markets. Metrohm NIRS analyzers are compliant with USP <856>, and the Vision air complete package is 21 CFR Part 11 compliant.

Read more about NIRS compliance with 21 CFR Part 11 in our related blog post below.

NIR spectroscopy: a 21 CFR Part 11 compliant tool for QC and product screening

Which ASTM test method makes NIRS a QC compliant tool?

ASTM E1655 (Standard Practices for Infrared Multivariate Quantitative Analysis) is a guide for the multivariate calibration of infrared spectrometers used for determining physical or chemical characteristics of materials. These practices are applicable to analyses conducted in the near-infrared (NIR) spectral region (roughly 780 to 2500 nm) through the mid-infrared (MIR) spectral region (roughly 4000 to 400 cm^-1).

Applications and parameters for QC of personal care and cosmetic products with NIRS

Personal care products and cosmetics are subjected to standardized test methods to determine their chemical, physical, and tribological properties. Laboratory testing is an indispensable part of R&D and QC. The following test parameters are typically important for many end products in this industry, and can be measured with NIRS (Table 1).

Reference

[1] Cosmetics Business; Euromonitor. Global Major Beauty and Personal Care Market 2020.

Your knowledge take-aways

On-demand webinar: Faster & Easier: Quality Control of Personal Care Products by Near-Infrared Spectroscopy