Sunless tanning products have come a long way from their initial debut on the cosmetic market in 1959.1, 2 Dihydroxyacetone (DHA) remains the most effective and popular ingredient for providing a sunless tan, despite the numerous challenges the ingredient poses for the cosmetic formulator. Early sunless tanning products suffered from problems with unnatural, dark orange tones and uneven deposition of color. These issues led formulators to develop daily moisturizers that gradually provided a more natural color. Such products became so successful that consumer demand resulted in product shortages and caused eBay bidding wars.3
Other approaches to improving the artificial tanning process have included the use of amino acid derivatives and antioxidants in combination with DHA to accelerate the browning reaction, thus more closely replicating the tonality of a natural tan.4, 5 However, there are still challenges to formulating with DHA that must be overcome. Following is a review of those challenges—including formulation stability, malodor produced during the browning reaction, compatibility issues with sun protection ingredients, and the generation of free radical damage. In addition, the author suggests some solutions to these challenges.
Sunless tanning products can be delivered in a variety of vehicles including lotions, gel-creams, sprays, wipes and foams. In aqueous solutions, DHA tautomerizes to structural isomer glyceraldehydes and because aldehydes are very reactive, solutions containing DHA are sensitive to a variety of formulation factors including pH, heat, polymeric thickeners, fragrance, nitrogen-containing compounds and metal oxides (see Figure 1).6, 7 Since many of these factors are often compounded in formulations, they complicate the ability of formulators to stabilize the shelf life of formulas containing DHA. Furthermore, the degradation of DHA can lead to the production of potential skin irritants such as formaldehyde, formic acid and acetic acid, thus emphasizing the importance of stabilization.8
Adjusting the pH level of formula to a value between 3 and 4 is optimal for the stability of DHA; however, buffering the system has been found to be counter-productive. Recent evaluations using perfluoropolyether phosphate (PFPE) to adjust the pH of DHA-containing formulations have shown increased pH stability with minimal degradation of the colorant during storage for two years, and less irritation potential than formulations prepared using lactic acid to adjust the pH.7 Although this study does not appear to have evaluated stability under accelerated conditions, which is standard for the industry, these initial findings suggest that PFPE could be a suitable option for stabilizing the pH of DHA-containing sunless tanning preparations.
In addition to the development of odor due to the degradation of DHA in formulations, an unpleasant and characteristic odor can develop on skin during the browning reaction. It has generally been surmised that the generation of the odor is correlated to color development and therefore necessary.9 Many attempts have been made to conceal this odor with masking fragrances or increased levels of fragrance but fragrances themselves can be undesirable or a source of potential irritation.
To sequester the offending odor molecules in sunless tanning formulations, cyclodextrins have been utilized.10 Complexation of cyclodextrins with flavor chemicals can be achieved by simply mixing the two in an aqueous solution.11, 12 While cyclodextrins could improve the shelf stability of formulations by absorbing degradation products over time, it is unclear whether they are available to sequester the malodor that forms hours after application of the sunless tanner. A brief survey of product reviews on consumer Web sites shows that malodor reduction remains one of the top challenges for formulators of sunless tanning products.
Sun Protection Factor
Sunless tanning products often are recommended as a safer alternative to tanning beds and UV-induced natural tans. However, a survey of young adults ages 18 to 30 indicated that use of sunless tanners does not necessarily decrease the use of tanning booths or incidence of sunburn. In fact, approximately one-third of sunless tanning products users and non-users surveyed believed that these products provided the user with protection from the effects of the sun, including sunburn.13 This finding suggests that use of sunless tanners does not necessarily increase sun protective behavior, and while two applications of a cream containing 20% DHA have been shown to provide a sun protection factor (SPF) of 3, most sunless tanning products on the market contain less than 5% total DHA.2, 14
Sunless tanners may be an effective alternative to UV-induced tanning but as is generally known, they should not be used in place of sunscreens.2 Accordingly, the US Food and Drug Administration requires the following statement on sunless tanning products that do not contain sunscreens: “Warning—This product does not contain a sunscreen and does not protect against sunburn. Repeated exposure of unprotected skin while tanning may increase the risk of skin aging, skin cancer, and other harmful effects to the skin even if you do not burn.”
Applying sunscreen after the use of sunless tanning products is recommended, and some dermatologists have suggested that the addition of sunscreen actives to sunless tanners should be mandated. There are currently only a few sunless tanning products on the market that offer adequate sun protection.12, 15 This may be due to DHA’s incompatibility with inorganic sunscreens—e.g., zinc oxide catalyzes the degradation of DHA, which reduces the number of options for providing full-spectrum UVA/UVB protection.1 The cost alone of employing both DHA and sunscreen actives may also be prohibitive in mass retail markets. Thus, the development of sunless tanners with adequate sun protection properties remains an area open for innovative solutions.
Free Radical Formation
Photodamage, including the accelerated skin aging and increased risk for skin cancer associated with UV exposure, has been well-documented. In particular, UV generated reaction oxygen species (ROS) have been linked to collagen degradation and the induction of matrix-metalloproteinases.16, 17 Recently, concerns over the generation of free radicals during the Maillard Reaction—i.e., the process through which DHA browns the skin—have made their way into the media.18 In vitro studies of murine skin treated with DHA solutions at 2-hr intervals for 8 hr resulted in the generation of free radicals.19 Researchers also showed, in an ex vivo study, a 180% increase in free radical generation in UV-exposed skin treated with 20% DHA.20 Again, this data was generated with levels of DHA at concentrations well above those experienced by the consumer from self tanning products but their perceptions still may have been influenced. The utilization of encapsulated DHA liposomes or sunless tanners formulated to include topical antioxidants or sunscreens, particularly those with activity in the UVA range, could mitigate the production of free radicals.19
Although sunless tanning products utilizing DHA have been on the market for 50 years, DHA’s inclusion still presents formulators with many challenges in developing effective products. Much potential exists for future innovative solutions to solve these challenges.
- T Kurz, Formulating effective self-tanners with DHA, Cosm & Toil 109(11) 55-61 (1994)
- ZD Draelos, Self-tanning lotions: Are they a healthy way to achieve a tan? Am J Clin Dermatol 3(5) 317-8 (2002)
- J Bennett, The scoop on self-tanners (2005), Washington Post Web site, available at www.washingtonpost.com/wp-dyn/content/article/2005/05/25/AR2005052501236.html (accessed Jan 29, 2010)
- MF Bobin and J Cotte, Effects of color adjuvants on the tanning effect of dihydroxyacetone, J Cos Sci 35 265-272 (1983)
- N Muizzuddin, KD Marenus and DH Maes, Tonality of suntan vs. sunless tanning with dihydroxyacetone, Skin Res Technol 6(4) 199-204 (2000)
- RK Chaudhuri, Formulating with dihydroxyacetone (DHA), in Surfactants in Personal Care Products and Decorative Cosmetics, CRC Press: New York (2006) pp 325-339
- G Pantini etal, Sunless tanning products containing dihydroxyacetone in combination with a perfluoropolyether phosphate, Int J Cosmet Sci 29(3) 201-9 (2007)
- A Ostrovskaya, AD Rosalia, PA Landa and D Maes, Stability of dihydroxyacetone in self-tanning cosmetic products, J Cos Sci 47 275-278 (Jul/Aug 1996)
- M Caswell, Sunscreen formulations and tanning formulations, in The Chemistry and Manufacture of Cosmetics, Vol 2, ML Schlossman, ed., Allured Business Media: Carol Stream, IL USA (2000) pp 73-99
- PJ Letini, JRZ Skin tanning compositions and methods for their preparation and use, US patent 5514367 (1996)
- D Baines, Chemistry and Technology of Flavors and Fragrances, DJ Rose, ed., CRC Press, Boca Raton, FL: (2005)
- TA Reineccius, GA Reineccius and TL Peppard, Encapsulation of flavors using cyclodextrins: Comparison of flavor retention in alpha, beta and gamma types, J of Food Science 67(9) 3271–3279 (2002)
- K Brooks et al, Use of artificial tanning products among young adults, J Am Acad Dermatol 54(6) 1060-6 (2006)
- A Faurschou and HC Wulf, Durability of the sun protection factor provided by dihydroxyacetone, Photodermatol Photoimmunol Photomed 20(5) 239-42 (2004)
- Z Dajani et al, Sun protection factor content and warning statements for sunless tanning products: An examination of retail outlets and the Internet, J Am Acad Dermatol 53(5) 919-20 (2005)
- HS Black, Potential involvement of free radical reactions in ultraviolet light-mediated cutaneous damage, Photochem Photobiol 46(2) 213-21 (1987)
- M Wlaschek et al, Solar UV irradiation and dermal photoaging, J Photochem Photobiol B 63(1–3) 41–51 (2001)
- NChao, Sun day school: The best products for summer (2008), Marie Claire online, available at www.marieclaire.com/hair-beauty/how-to/tips/best-sunscreen-products (accessed Apr 26, 2010)
- RV Lloyd, AJ Fong and RM Sayre, In vivo formation of Maillard reaction free radicals in mouse skin, J Invest Dermatol 117(3) 740-2 (2001)
- K Jung et al, UV-generated free radicals (FR) in skin: Their prevention by sunscreens and their induction by self-tanning agents, Spectrochim Acta A Mol Biomol Spectrosc 69(5) 1423-8 (2008)