CHAPTER 20
Sunless Tanning Products

Peter Foltis, Angelike Galdi, and Christian Oresajo

L’Oréal Research and Innovation, Clark, NJ, USA

Introduction

Social norms for tanning in the United States have dramatically changed in recent times. The presence of a tanned body at one time conveyed the social status of an outdoor laborer. Now, having a tan, especially during the winter months, indicates affluence.

More information has become available regarding the deleterious effects of ultraviolet (UV) exposure [1–3]. The public is beginning to understand the dangers, thereby modifying their lifestyle choices toward safer practices. However, the change has been slow because sun exposure behavior is in part influenced by psychologic and societal factors [4–6]. Self‐tanning preparations are becoming an increasingly important option for those desiring the tanned look while not exposing themselves to undue harm.

Sunless tanning products

Definition

Sunless tanning products, or self‐tanners, are preparations that when applied topically impart a temporary coloration to the skin mimicking skin color of naturally sun‐tanned skin. Depending on the formulation and the active ingredients, the onset of color formation can be from 30 minutes to several hours and can last up to 1 week.

The reaction of dihydroxyacetone (DHA) with human skin and amino acids was first described in 1961 [7]. Self‐tanningformulations were introduced soon after. Consumers’ acceptability soon waned because of unattractive results such as orange hands, streaking, and poor coloration. Because of these drawbacks, consumers today still associate sunless tanning with these undesirable results. However, improved formulations have appeared on the market. Refinements in the DHA manufacturing process and advancements in formulation science have aided in the creation of formulations that produce a more natural‐looking color and better longevity.

Active ingredients

The most widely used and most efficacious active ingredient in self‐tanners is DHA. It is the only ingredient that is currently recognized as a self‐tanning agent by the US Food and Drug Administration (FDA) [8]. DHA‐based sunless tanners have been recommended by the Skin Cancer Foundation, the American Academy of Dermatology Association, and the American Medical Association [9–11]. DHA is a triose and is the simplest of all ketoses (Figure 20.1).

Mechanism of action of DHA

Ketones and aldehydes react with primary amines to form Schiff bases [12]. This is similar to the Maillard reaction, also known as nonenzymatic browning, and involves, more specifically, the reaction between carbohydrates and primary amines [13].

Schematic illustration of chemical structure of dihydroxyacetone (DHA). — **Figure 20.1** Chemical structure of dihydroxyacetone (DHA).

DHA is able to penetrate into the epidermis because of its size. Pyruvic acid is formed from DHA and either can react with sterically unhindered terminal amino groups in the amino acids of epidermal proteins. The epsilon amino group of lysine and the guanido group of arginine are particularly susceptible to nucleophilic attack by the reactive carbonyl oxygen. Epidermal proteins contain high concentrations of both of these amino acids. Based on photoacoustic depth profilometry, the tanning effect of DHA begins in the deeper part of the stratum corneum layer (15–22 μm) before expanding over the entire stratum corneum and stratum granulosum [14, 15]. Subsequent steps of the reaction mechanism are not fully understood. The resultant products are brown in color and are collectively referred to as melanoidins.

Dihydroxyacetone attributes

Regulated by US FDA as a color additive; only approved color additive for self‐tanners.
Triose with favorable physico‐chemical properties (mwt < 100; nonionic) for reaction in epidermis.
Reacts with sterically unhindered terminal amino groups in the amino acids of epidermal proteins. The epsilon amino group of lysine and the guanido group of arginine are particularly susceptible to nucleophilic attack by the reactive carbonyl oxygen.

Alternative actives

As previously stated, US federal regulations recognize only DHA as a sunless tanning agent [8]. Alternative technologies exist with the capability to impart an artificial tan to the skin.

Reducing sugars other than DHA can act as Maillard reaction intermediates and therefore have the potential for use as sunless tanning agents [16]. Reducing sugars, in basic solution, form aldehydes or ketones. This allows the sugar to act as a reducing agent in the Maillard reaction of nonenzymatic browning. Reducing sugars include glucose, fructose, glyceraldehyde, lactose, arabinose, and maltose.

Unfortunately, a large amount of heat energy is required to trigger the glycation reaction between glucose, the most commonly known reducing sugar, and free amines. Such properties render many reducing sugars useless for sunless tanning products. An exception is the keto‐tetrose, erythulose. Although this reducing sugar can enhance naturalness of color, it does take longer to produce results than DHA. Thus, erythulose has been used in combination with DHA. Presumably, erythulose follows the same pathways as DHA in developing coloration.

Formulation challenges

The content of DHA in self‐tanning products depends on the desired browning intensity on the skin and is normally used in the range 4–8%. Depending on the type of formulation and skin type, a tan appears on the skin about 1–3 hours after use. During product storage, the pH of a DHA‐containing formulation will drift over time to about 3–4. At this pH, DHA is particularly stable. In order to ensure end‐product stability, certain key factors must be considered.