Alcohols in cosmetic formulations

Alcohol, in its many forms, is used in skin care and cosmetic formulations for a variety of purposes, and the presence of these substances in formulations is always the source of discussion concerning their claimed beneficial or adverse properties.

The use of alcohols in cosmetic formulations is to frequently misunderstood, as the popular conception of alcohols is that of solvents that dry and irritate the skin. While this is true in the case of many commercial and industrial alcohols, it is important to understand the particular properties of the different alcohol commonly found in cosmetic products, and the roles they play in the formulations.

Simple Alcohol

Simple alcohol such as ethyl alcohol, isopropyl alcohol (rubbing) and denatured alcohol (SDA) are derived from the fermentation of sugars, starches and other carbohydrates. Their major property is that of an antibacterial, but they are also excellent solvents of fats and lipids, and are consequently used in formulations to help remove excess oil. When applied in sufficient quantities and frequency, they may induce dry skin conditions.
Simple alcohol are very thin and water like. They are very volatile and will therefore evaporate very quickly. This rapid evaporation gives astringents the perception of a “tightening” effect.
Denatured alcohol or SDA alcohol is often marketed as being special and different than other alcohols, but are simply alcohol that have been rendered undrinkable by the addition of a denaturant such as denatonium benzoate. Their other properties are largely unchanged.
Simple alcohols are commonly used medically as antiseptics, and in a wide variety of cosmetic products such as toners, fresheners, perfumes, suntan lotions and deodorants. In addition to acting as a solvent, they are used as thickeners or texturisers in conjunction with other ingredients.
Because these alcohols are solvents of sebaceous and epidermal lipids, conditions of sensitivity and lipid dryness will contraindicate the use of products containing high quantities of these substances. (Cleansers, toners etc) It is because of this reason that “alcohol free”cleansers and toners are popular.
Many forms of acne that exhibit low levels of surface lipids will also generally suffer adverse reactions from the application of alcohol rich formulations.

Non drying alcohol

There are another group of more complex alcohols known as fatty alcohol which exhibit emollient and occlusive properties when used in cosmetic formulations.
These non-drying alcohols have a more complex molecular structure than simple alcohol, and are generally derived from both animal and marine sources or synthesized from chemical substitutes. In their raw state they generally have a thick, waxy texture, although some are almost solids at room temperature.
These thicker, more substantial substances are used in formulations to achieve a smooth velvety feel, and are usually a major emollient or emulsifying portion of cosmetic formulations with a creamy consistency. Their occlusive properties help trap moisture and slow down the transdermal water flow.

Common fatty alcohols include caprylic, cetearyl, cetyl, decyl, isostearyl, lauryl, myristyl, oleyl and stearyl alcohols.
Some fatty alcohols (oleyl, isostearyl, lauryl) exhibit varying degrees of comedogenicity, and when used in high quantities in formulations, may cause adverse reactions on acne prone skins.

Conclusions

There are essentially two types of alcohol found in cosmetic formulations that exhibit diverse properties. The light, volatile alcohols are employed for their antiseptic, astringent, fat and lipid solvent properties, while the heavier emollient alcohols are used for their occlusive and lubricating properties.
Logically, application of the lighter alcohols in sufficient quantities and frequency will dry susceptible skins. However, these alcohols do not show adverse drying effects when used in lower concentrations in conjunction with other moisture binding substances.
The heavier fatty alcohols exhibit beneficial occlusive properties and provide a smooth feel when applied to the skin. Certain types in high concentrations should be avoided for use on specific skin conditions such as oily or acne prone.

Alcohols have a definite place in cosmetic formulations, and the use of formulations containing them will be dependant upon the result the therapist wishes to achieve in relation to the skin condition she is treating. 

References:

1. John Knowton, CChem MRSC & Steven Pearce, Bsc, CChem, MRSC: Handbook of Cosmetic Science & Technology.
2. Monroe Lanzet, PhD: Comedogenic effects of raw materials. Cosmetics & Toiletries Journal.
3. Ruth Winter: Dictionary of cosmetic ingredients.
4. Dr Andrew Scheman & David Severston: Cosmetics buying guide.