Skin Types
Toners have two key formulating challenges—formulating for specific skin types and vehicle/ingredient stability and compatibility. Varying skin types, including dry, normal, oily, combination, sensitive, and acne-prone, require different and skin-type specific ingredients and vehicles. Free radical scavenging antioxidants are used regardless of skin type. Most toners are used within a skin care regimen. The patient’s concern about toners being drying or harmful may be mitigated by using a regimen and toner appropriate for skin type.
Alcohol-free formulas with humectants, emollients, and soothing agents are most suitable for the dry and sensitive skin patient (Table 2). This, in conjunction with the use of a moisturizer, allays the concern of a toner being drying. The addition of humectants and emollient agents will help maintain moisture balance. Soothing ingredients are beneficial to alleviate the redness and irritation often experienced with these skin types. Sensitive
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Table 2 Skin Toner for Dry Skin
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skin toners are formulated similar to dry skin formulas with the addition of anti-irritants such as allantoin, green tea, or licorice extract.
Toners designed for normal to combination skin types typically contain low levels of ethanol, humectants, and appropriate key ingredients. Botanical extracts with high tannin levels offer skin tightening effects without stripping the skin of its natural oils to mitigate the potentially drying effect of ethanol. It is recommended that soothing agents and humectants be added and that toner use be followed by a moisturizer designed for normal skin.
Oily skin toners, such as the formula in Table 3, are designed to provide a high degree of astringency and to control and/or remove excess sebum. This is achieved by using higher levels of ethanol and highly astringent and oil-absorbing ingredients. Levels of 20-50% ethanol may be used. The sebum removing and cooling effects of ethanol are highly desirable to the oily skin patient. High tannin-containing ingredients provide astringency. Astringent botanicals to consider include extracts of witch hazel, rosemary, lemon, grapefruit, horse chestnut, and stinging nettle. Natural sources of glycolic acid found in sugar cane extract, lactic acid found in milk, and salicylic acid found in willow bark extracts are often added for exfoliation. If a stimulating sensation is desired, peppermint, menthol, or eucalyptus is added. Kaolin, polyamides (nylon-6 and -12), methylmethacrylate crosspolymer, and silica absorb skin oil and minimize the appearance of oily shine on the skin. Silica settles slowly and gives the product a hazy appearance. The other oil-absorbing particulates settle readily, so a shake-well instruction prior to use is required. Soothing botanical agents and allantoin may be added to lessen any irritating dryness associated with higher ethanol concentrations.
Toners formulated for acne-prone skin typically contain high levels of ethanol, salicylic acid, and naturally derived antibacterials such as cinnamon, neem, and tea tree oil. Recently, there have been several references on the allergenic characteristics of tea tree oil (18-21). The ethanol level should be kept to the minimum necessary to solubilize the salicylic acid in order to minimize excessive drying to the skin. The FDA OTC Acne Monograph (3) dictates levels of salicylic acid from 0.5-2.0% as well as the acne treatment claim that may be listed on the product. A pH <4 is needed to assure delivery of the acid form. Formulations containing salicylic acid typically use 35-60% ethanol to maintain its solubility and stability. Levels as low as 20% ethanol in conjunction with the humectants glycerin and butylene glycol as cosolvents have been shown to provide acceptable salicylic acid solubility at room-temperature and low-temperature (5°C) conditions (22). To further enhance the perception of medicinal benefits of an anti-acne toner, scent and skin sensorial-stimulating agents such as menthol, eucalyptus, peppermint, or camphor may be added. Soothing botanical extracts and humectants are beneficial to minimize the potentially irritating and drying effects of high alcohol levels.
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Table 3 Skin Toner for Oily Skin
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Alcohol-free toners may be used as a last step in cleansing, a preparation step to moisturizing, or as a whitening treatment product in the Far East. Toners are frequently sold under the “softener” nomenclature in Asia. Asian consumers have a negative perception of alcohol in terms of both skin reactions and odor of ethanol. They exhibit a higher degree of sensitivity to the skin effects of alcohol (23). It is advisable to avoid the use of alcohol and sensorial-stimulating agents to minimize the chance of irritation. Botanical extracts and the quasi-drug ascorbyl glucoside are used for whitening effects in toners. Another popular toner form in Asia is the lightweight, low-viscosity milky lotion. These are frequently used to prepare the skin as the first step of the moisturizing regimen. The milky lotions are alcohol-free. Collagen, hyaluronic acid, and whitening agents are popular in these products.
Ingredient and Vehicle Stability and Compatibility Considerations Requirements of pH, ingredient solubility and compability, and product stability influence the choice of ethanol-to-water ratios, humectants, and cosolubilizers. Hydroxy acids require low pH to be effective as exfoliants. Fortunately, they also act as pH adjusters when a low pH is desired. This low pH limits the choice of film formers and thickeners. There are also pH and concentration limitations when using AHAs in retail products sold in the U. S. The Cosmetic, Toiletry, and Fragrance Association’s Cosmetic Ingredient Review (CIR) Expert Panel recommends that cosmetic products containing glycolic and lactic acids and their salts and esters be formulated at pH >3.5 and at concentrations < 10% (24). Oil-soluble ingredients such as emollients, fragrance oils, and vitamins A and E require cosolubilizers to assure ingredient solubility to maintain product clarity and stability. The use of these cosolubilizers may cause product foaming during production filling and consumer use. This foaming can be minimized by adding an ingredient such as simethicone to reduce surface tension. Tea tree oil, found in many anti-acne and oily skin toners for its antibacterial activity, requires solubilizing agents for a clear solution, has a distinctive odor and its terpene constituents are highly susceptible to oxidation. The oxidation potential impacts the safety of the product (18-21); therefore, a recent European Cosmetic Toiletry and Perfumery Association (COLIPA) report recommended that manufacturers add antioxidants and/or packaging that minimizes the product’s exposure to light (25).
High levels of ethanol in a toner can solubilize oil-soluble ingredients without the need for additional cosolubilizers. Easier to use water-soluble botanical extracts are more commonly used to provide antioxidant, anti-irritant, and soothing benefits, thus negating the need for cosolubilizers and mitigating any drying effects of alcohol. Alcohol-free toners or toners with less than 20% alcohol require preservatives to maintain microbiological quality.