Formulating with Natural Colors

It seems appropriate that this contribution on natural colors is being written as the author is surrounded by autumn foliage in the Hudson River Valley. The brilliant golds, reds and shades of orange that replace summer’s diverse bright greens draws an impressive caravan of city dwellers every weekend to view Nature’s display and pick apples. The chromophores that generate these appealing colors in nature can also function as natural colorants in cosmetics. Ethnographers have concluded that prehistoric people decorated their bodies with pigments long before they began wearing clothing. “Body painting only requires the availability of pigments and imagination,” wrote Jablonski, who also referenced the archaeological discovery of pigments dating to 75,000 years ago.¹

Cosmetic chemists often use color to tint solutions and emulsions, or to add pigment to cosmetics for skin application. To do so, they must be aware of the commercially available materials and know which are allowed under local regulations. From a natural certification perspective, the guidelines promulgated by certifying bodies also should be considered.

Dye vs. Pigment

Before exploring the role of natural colorants in cosmetics, it is important to review the difference between a dye and a pigment. Dyes are soluble molecules that produce color by transmitting observable wavelengths and absorbing those that are unseen. For example, chlorophyll molecules absorb primarily in the blue and red regions of the visible spectrum, and transmit in the green region.² In contrast, pigments essentially are opaque insoluble particles that produce effects by reflecting the perceived color and absorbing the remainder of the visible spectrum. Most powdered particles appear as variations of white since they scatter all visible wavelengths; so whether they are titanium dioxide, powdered sugar or fine salt crystals, these materials appear as variants of white to the human eye.

Alternatively, a material that absorbs all visible wavelengths and reflects none appears black. This phenomenon is less common. Interestingly, formulators of color cosmetics consider carbon black as being much blacker than iron oxide black due to the differences in light absorption. As any chemist who has scooped carbon black from a partially full bag can attest, it is difficult to accurately see where the powder level begins because virtually no light is reflected.

Colorants and Regulations

While a wide range of colorants is available, regulatory constraints limit the number allowed in personal care. The natural colors that are acceptable by the U.S. Food and Drug Administration (FDA) for cosmetic use and do not require batch certification—including nature-identical, naturally derived, organic and inorganic—are cited in Part 73, Subpart C (Cosmetics) of Title 21, of the U.S. Code of Federal Regulations (CFR).³ Synthetic colorants, listed in Part 74 of the same document, require individual batch certification for purity by the FDA in order to be approved for food, drugs and cosmetics (F, D&C), or drugs and cosmetics (D&C). Synthetic colorants are not considered here, since they are all off limits for natural formulations per the main certifying bodies. Even within the Part 73, Title 21 CFR list of allowed colors, many are synthetic, limiting their use. The European Union (EU) also has a list of 153 approved colors, including synthetic, natural, organic and inorganic, subsumed in its Annex IV: List of Colorants Allowed in Cosmetics.⁴ Table 1 and Table 1 (cont.) identifies the natural or nature-identical colorants included in these U.S. and EU lists with their color index (CI) numbers, if available.

The latest COSMetics Organic and natural Standard (COSMOS), version 2, October 2013, does not specify approved colorants but COSMOS Appendix IV provides a list of acceptable inorganics that includes most conventionally used pigments. Organic species such as the carotenoids are presumed to be acceptable if they are naturally derived. The caveat for allowing ingredients of mineral origin, as outlined in section 6.1.2, is that they “are obtained without intentional chemical modification and preferably from environmentally sound extraction processes.” Further, they may be “treated with the physical processes” listed in COSMOS Appendix I.

Notwithstanding the implication that some eye shadows and foundations use minerals directly from nature, no one is scraping rust from old iron pipes or grinding up mineral ores from the ground and formulating them into finished color cosmetics. These mineral pigments must be extracted and purified to meet the strict standards spelled out in Part 73 of the CFR, and they must function effectively to reveal their pure color values. In other cases, the synthesis of mineral pigments is outlined in a brief monograph, or they are specifically identified as being synthetic.^{5, 6} NaTrue standards also identify nature-identical inorganic pigments allowed in natural cosmetics, with citations of occurrences in nature to validate their natural status.⁷

Organic Pathways to Color

Here, some specific natural colors are reviewed; readers are reminded to refer to the relevant lists for regulatory acceptance in the United States, EU, etc. The colors found in plants and animals fall into a few limited chemical categories resulting from distinct metabolic pathways.

Porphyrin pathway: One route is the porphyrin pathway, through which 8-aminolevulinic acid residues, formed from glutamic acid or glycine, are condensed and cyclized into a large macrocyclic ring with magnesium at its center to yield the family of chlorophylls central to photosynthesis. Analogously, other porphyrin rings include heme, with iron at its core, the metallo component of hemoglobin, cytochrome and other metalloproteins. Both the United States and EU allow a water-soluble variant, chlorophyllin copper complex, as a green color. It also is used for deodorizing properties.

Isoprene pathway: Another major route is the isoprene pathway, notably the source of many terpenoid compounds that form the base of aromatic essential oils. Larger isoprene polymers such as C₄₀, with eight isoprene units, yield the family of carotenoid pigments. These are oil-soluble and absorb in the shorter blue wavelengths, imparting shades of yellow, orange and red. Although they are not specifically cited in many of the natural certifying organization standards, naturally sourced carotenoids presumably would be acceptable.⁸

Familiar colors in this group—many of which are acceptable for cosmetics, food and drugs either in the United States or EU—include beta-carotene, a yellow-orange precursor of vitamin A; norbixin, found in annatto, which is orange; astaxanthin, a red color used in aquaculture; red lycopene, from tomatoes; yellow lutein; red canthaxanthan, once used in oral tanning; reddish-orange capsanthin and capsorubin, from paprika extract; and yellow-orange rubixanthin. These are all oil-soluble dyes with varying levels of antioxidant activity, suggesting their use as free radical scavengers in addition to colorants—although in most cases, their deep color limits the amount used in most products.

Phenylpropenoid/flavonoid pathway: Another large group of colors is derived from the phenylpropenoid/flavonoid pathway. This route gives rise to the family of plant polyphenols—including the yellow flavonol fisetin, cited as a colorant in the expanded list of EU cosmetic ingredients; and red and blue anthocyanins, a number of which are listed as acceptable EU colorants. Plant polyphenols also demonstrate in vitro antioxidant activity, as noted in the previous carotenoids discussion, and these properties can be alternative uses for colorants to avoid listing them on product labels as color additives. Analogous soluble yellow plant colors include anthoxanthins, one interesting commercial range^a of which takes advantage of the dual functionality of these polyphenols. This trio includes a red colorant with antioxidant properties from Rubia tinctorum; a yellow colorant from Genista tinctoria; and a blue colorant from Genipa americana fruit.

Betalain pathway: Lastly, betalains are an unusual group of pigments derived from the nitrogen-containing amino acid tyrosine. These pigments range in color from yellow betaxanthins, to red and violet betacyanins; they are notably present both in the flowers and fruits of cacti. The deep, dark red of Beta vulgaris (beet) roots comes from the betalain betanin—the glycoside of the aglycone betanidin, which is on EU list of colors allowed in cosmetics.

Additional pathways: There are a few additional natural and organic colorants that find their way onto the cosmetic chemist’s palette. Carmine is the stable red color derived from shells of the scale insect Dactylopius coccus costa, which feeds on the Opuntia cactus in Mexico. Kermes—a similar if not identical red dye—originates from the Mediterranean region, and also is derived from female scale insects. Here, the content of the dye carminic acid can be present at > 20% dry weight. Carminic acid is a glycoside of an acidic polyphenol that is converted into an insoluble lake by reacting it with calcium. Additionally, curcumin is a yellow colorant derived from turmeric—the polyphenolic structure of which gives it significant antioxidant properties, as with the flavonoids. Turmeric is also reputed to have anti-inflammatory properties that suggest its use in nutritional supplements as well as cosmetics.

Acceptable Inorganics

Beyond the organic colorants described lies a full range of inorganics. As cited previously, these apparently are acceptable since they occur in nature as complex minerals—which, in their pure form and when used as pigments, would not pose safety issues to either skin or the environment. However, restrictions become a factor when using nano-sized particles of these inorganics; i.e., particles having any dimension less than 100 nm. The formulator should also be aware of the accepted status of pigment coatings, which may be applied to inorganics to aid in their dispersion in lipophilic media. Silicone and reactive silane coatings would likely be prohibited in natural formulations, whereas lecithin and other natural lipids such as jojoba oil should be acceptable.

Pearlescent pigments also appear to be allowed by regulatory agencies and natural certifiers. Mica and titanium dioxide are acceptable, as is their physical combination in laminated pigment platelets—including hybrids with additional inorganic pigments. Some pearlescent pigments have achieved Ecocert certification as well; bismuth oxychloride appears on the 21 CFR Part 73 Cosmetics subpart C list; the EU Annex IV; and charts identifying inorganic pigments accepted by NaTrue and COSMOS, which brings most of these combination pigments into compliance.

Although not colored itself, dihydroxyacetone (DHA) can be considered a color precursor, since it is treated as a colorant in the U.S. regulations per the 21 CFR Food & Drugs, Part 73—Listing of Color Additives Exempt from Certification Subpart C Cosmetics section 73.2150.³ The only restriction for DHA is that it must be used according to good manufacturing practices to externally impart color to the human body. It is not listed as a colorant in the EU, but the cosmetic ingredient (COSING) website⁹ lists it as one of three tanning agents, and the Scientific Committee on Consumer Safety (SCCS) has published an opinion that it is acceptable for use up to 10%.¹⁰

DHA is a colorless keto compound, a ketose, derived from glycerin that reacts with proteins and amino acids to form colored compounds, termed melanoidins, via the Maillard reaction. Commercial DHA is made via the fermentation of vegetal glycerin by species such as Gluconobacter oxydans. The retailer Whole Foods allows the use of DHA in the regular body care products its markets, but not in products designated as “premium” body care.¹¹ One commercially available DHA^b that is Ecocert-approved uses plant-based starting materials and ethanol for purification and non-genetically modified bacteria for fermentation. Although not a true color itself, DHA could be considered a viable option to include in the range of natural ingredients designed to impart color to skin.

Summary

Formulators striving to create and certify color cosmetics as natural have limited options. However, they should be more concerned with formulating a base having acceptable ingredients—especially emulsifiers and preservatives—than with pigment and color choices, to produce a range that is acceptable to both regulators and natural product certifiers. In the near future outlook, technologies will allow formulators to work within these regulatory and natural guideline boundaries—with creativity to yield mixtures that achieve novel effects. Manipulation of existing compounds within the acceptable physical and chemical processes may reveal new visions that tempt the consumer.

References

1. G Nina et al, Skin: A Natural History, University of California Press (2006) pp 143-148
2. D Lee, Nature’s Palette: The Science of Plant Color, University of Chicago Press (2007) p 66
3. www.ecfr.gov/cgi-bin/text-idx?c=ecfr&​SID=fc2869830da702969a2dcfdeb71d7594&​rgn=div5&​view=text&​node=21:1.0.1.1.27&​idno=21#21:1.0.1.1.27.3 (Accessed Nov 25, 2013)
4. https://commission.europa.eu/about-european-commission/departments-and-executive-agencies/justice-and-consumers_en/index.cfm?​fuseaction=search.results&​annex_v2=IV&​search (Accessed Nov 18, 2013)
5. www.fda.gov/Cosmetics/​Guidance​Compliance​Regulatory​Information/​Voluntary​Cosmetics​Registration​ProgramVCRP/​OnlineRegistration/​ucm109084.htm (Accessed Nov 18, 2013)
6. www.cosmeticsandtoiletries.com/​formulating/​function/​pigment/​118610674.html (Accessed Nov 18, 2013)
7. www.natrue.org/​fileadmin/​natrue/​downloads/​Criteria_2.8/NATRUE-​Label_​Requirements_​V2-8_EN.pdf (Accessed Nov 18, 2013)
8. Ibid Ref 2, pp 56-80
9. https://commission.europa.eu/about-european-commission/departments-and-executive-agencies/justice-and-consumers_en (Accessed Nov 25, 2013)
10. http://ec.europa.eu/​health/​scientific_​committees/​consumer_​safety/​docs/​sccs_o_048.pdf (Accessed Nov 25, 2013)
11. www.wholefoodsmarket.com/​department/​article/​whole-body-quality-standards (Accessed Nov 25, 2013)