Toners are typically clear to translucent aqueous or hydroalcoholic solutions. The choice of ingredients, function of these ingredients, and claims determine the product’s appearance and type of solution. A generic base formulation is shown in Table 1. Water is typically the major component and main vehicle or delivery system for active or other cosmetically important ingredients. Ethanol may be added as part of the vehicle as desired for skin type and/or ingredient solubility. Ethanol is generally not used in toners formulated for dry or sensitive skin or in the Asia-Pacific market, but it is found at varying levels in normal, combination, oily, and acne-prone skin types. Ethanol also serves as a preservative when used at levels of 20% or higher. Various types of denatured ethanol are used in toners, depending on country regulations on the denaturant. Isopropanol was used years ago, but it is now out of favor because of its strong odor.
Humectants are added to attract moisture to the skin, mitigate the drying effects of alcohol, lower the freeze point to ensure stability in cold temperatures, solubilize other
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Table 1 Skin Toner—Base Formula with Typical Concentration Ranges
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ingredients, and adjust the aesthetics. Glycerin and sorbitol are the most cost effective humectants, but they can lend a tacky afterfeel. Sodium polycarboxylic acid (PCA) is less tacky, but more importantly, it is similar to the PCA which is found in the skin’s own natural moisturizing factor (NMF). When additional solubility and an elegant, smooth, non-tacky feel is desirable, propylene glycol, butylene glycol, polyethylene glycols, and the ethoxylated glycerins, such as methyl gluceth-10 or methyl gluceth-20, are used. Sodium hyaluronate and other water-soluble moisturizing agents may be added.
Emollients, such as dimethicone copolyols and small amounts of natural oils, are beneficial for skin lubricity and soothing. They require the use of cosolubilizers to assure ingredient solubility to maintain product clarity and stability. Cosolubilizers include ethoxylates and propoxylates, such as PEG-40 hydrogenated castor oil, PPG-5-ceteth-20, or polysorbate 20. They are added at concentrations of 0.10-0.50%, depending on the oil-soluble ingredient and level used. The ethoxylated and proproxylated humectants are also useful but less efficient cosolubilizers.
Botanical extracts are added for a variety of reasons (4-6). The concentration is dependent on many factors, including the type of extraction and the percent solids of the extract. For example, aloe extract and witch hazel distillate are often used as vehicles. Frequently, several botanicals will be incorporated into a toner. Some extracts are more suitable for specific skin types; some offer multiple benefits. They are frequently touted as the key ingredient that offers benefits such as astringency, anti-inflammation, antioxidant, exfoliating, soothing, and cooling. It is the extracts’ polyphenolic content that offers one or more of these benefits. Especially popular and beneficial are the polyphenolic bioflavinoids found in green tea, rosemary, blueberry, raspberry, strawberry, red wine, grapeseed, and pine bark extracts. They provide antioxidant and anti-inflammatory benefits. The anti-inflammatory benefits equate to soothing the skin by reducing skin stinging, itching, and redness. Extracts of honey, mallow, soy, aloe, lavender, green tea, algae, licorice, and chamomile may be added for their soothing and conditioning effects on the skin. The high tannin levels in botanical extracts such as witch hazel, sage, horsechestnut, and quercus lusitanica oak provide astringency. In addition to its astringency, the distillate of witch hazel, which contains 14% ethanol, also provides a cooling effect on the skin. It may be claimed as an OTC drug product astringent under the Skin Protectant Monograph (2), but both the distillate and extracts forms are more frequently used as a cosmetic ingredient in skin toners. Isoflavones, such as soy extract, known for their phytoestrogen content, are beneficial to more mature and dry skins.
Other beneficial ingredients used in toners are allantoin and panthenol for conditioning and soothing of the skin, and free radical scavenging antioxidants, such as alpha lipoic acid, superoxide dismutase, and vitamins A, C, and E. Vitamin E and its derivative, tocopheryl acetate, can also be used to protect the product and its constituents from oxidization.
Alpha-hydroxy acids (AHAs) such as glycolic, lactic, malic, citric, and mixed fruit acids are used for exfoliation and/or pH adjustment. While they are not marketed as toners, the toner product form has been used by aestheticians and dermatologists to deliver high levels of hydroxy acids in chemical peels for years, and more recently chemical peels with lower levels of AHAs have been introduced through the retail market. AHAs at efficacious exfoliating levels of pH < 5 may cause skin stinging and redness, so the addition of antiinflammatory and soothing botanical extracts is recommended. Although neutral pH ranges offer less irritation potential, they do not offer the same exfoliation activity. Polyhydroxy acids (PHAs), larger molecular weight variants of AHAs, are designed to be less irritating (7). Both AHAs and PHAs may be used in both aqueous and hydroalcoholic solutions. When used as a pH adjuster, AHAs are added at levels of 0.01-0.20%. The beta hydroxy acid (BHA), salicylic acid, is used for its keratolytic/exfoliating activity and is monographed as an OTC anti-acne drug (3).
Whitening agents have a long history of use in Asia. They are highly regulated in Asia as quasi-drugs. They have gained popularity in the rest of the world for the cosmetic claim of even skin tone, where the term whitening is considered a drug claim. Licorice, mulberry, and bearberry are popular skin lightening botanical extracts. The oil-soluble form of licorice at 0.05% is regulated as a functional drug in Korea (8). The water-soluble vitamin C derivatives, magnesium ascorbyl phosphate (MAP) used at 3%, and ascorbyl glucoside at 2%, are recognized as quasi-drugs in most of Asia (9). MAP is highly unstable and turns brown readily with time, high temperatures, and exposure to light. Ascorbyl glucoside is preferred for its acceptable stability profile.
Thickening ingredients are added when a slightly viscous and/or film forming property is desired. They also provide a more lubricious application and afterfeel than a solution. Xanthan gum, polyacrylic acids such as carbomer, and cellulose gum derivatives, such as methylcellulose, hydroxypropylcellulose, and hydroxyethylcellulose, are used.
Fragrance oils or naturally derived extracts and oils may be added to impart a pleasant scent to the formula or cover off-odors that develop when the product is exposed to excessive heat, light, or other parameters associated with shelf life. They also can be used to support a toner’s marketing position and enhance the message that the toner is soothing or refreshing or, in the case of anti-acne toners, medicinal. Rose and lavender extracts can be used for soothing and dry skin formulas. Rosemary, peppermint, and citrus extracts may be added to toners designed for oily and combination skins or when a refreshing, stimulating signal or scent is desired. Menthol, peppermint, and eucalyptus odors are associated with a medicinal benefit.
Like fragrance, color is included to deliver a sensorial signal, such as soothing, refreshing or therapeutic, or to enhance the product’s appearance, or to cover product color stability issues. Water-soluble Food, Drug, and Cosmetic (FD&C) and Drug and Cosmetic (D&C) colorants are used.