| | | | | levels of essential fatty acids, EFAs, are prized for |
| While global market for skincare and color | | | | their ability to replenish lipids (oils) that are found |
| cosmetics runs in billions of dollars and number of | | | | naturally within the skin layers. Linoleic acid is an |
| new products brought to market continues to | | | | example of an EFA. Long-chain alcohols, also called |
| expand exponentially, cosmetic chemists are | | | | fatty alcohols, are useful as emollients and |
| always looking for interesting and exotic | | | | emulsion stabilizers. Their polar hydroxyl groups |
| ingredients that improve skin's appearance and | | | | orient to the water phase with their fatty chains |
| health. A vast array of compounds is required to | | | | oriented towards the oil phase. Esters of fatty |
| supply these products. Every year hundreds of | | | | alcohols and fatty acids make excellent emollients |
| new ingredients are added to the list of those | | | | because of their low reactivity and good stability. |
| that have been used for centuries. Some | | | | Lanolin, derived from sheep's wool, is often called |
| materials used today can be traced to 11,000 | | | | wool grease. Lanolin has been used for centuries |
| B.C.E. in the animal drawings from the caves of | | | | due to its unique composition of complex sterols, |
| Altimira. | | | | fatty alcohols, and fatty acids. Cholesterol, a cyclic |
| The appearance of skin care formulation dates to | | | | molecule called a sterol, is a major component. |
| around 3000 B.C.E. in ancient Egypt. Most | | | | The polar hydroxyl groups of sterols and alcohols |
| concoctions were prepared from natural materials. | | | | enable the grease to absorb and hold water. Skin |
| Cleopatra is said to have bathed in donkeys' milk | | | | is primarily composed of water, countless oils and |
| to keep her skin smooth and supple. One naturally | | | | emollients are used to nourish and protect it. |
| occurring material used by the ancients was red | | | | The main distinction between moisturizers and |
| ochre, or iron oxide. Lumps of red ore were | | | | emollients is their solubility in water. Healthy skin |
| formed when iron oxidized or rusted. The red iron | | | | requires moisture. Moisturizers are generally polar |
| oxide was found in burial tombs in ceremonial lip | | | | materials that are hygroscopic in nature; they hold |
| tints and rouge preparations. It was also used to | | | | onto water. An important tool to assess the |
| draw the ancient cave pictures of animals, as | | | | efficiency of moisturizers is the high scope. It |
| seen in Altimira, and is still used in many makeup | | | | measures transepidermal water loss or TEWL. |
| formulations today. Eye paints have also been | | | | After a moisturizer is applied to the skin, the |
| found at ancient gravesites. These paints | | | | moisture level is recorded. After several minutes |
| consisted primarily of a copper-based green ore | | | | the moisture level will be reduced due to the |
| called malachite that was mined from nearby | | | | natural tendency of the skin to release moisture |
| quarries. Animal fat was combined with fragrant | | | | over time. Ingredients that can maintain a high |
| substances such as frankincense and myrrh to | | | | level of moisture in the upper layers of the skin |
| produce early skin ointments. More sophisticated | | | | for several hours can reduce the rate at which |
| creams and lotions were fine tuned through trial | | | | water is lost. Glycerin is a very cost-effective |
| and error and passed down over many | | | | ingredient used to help reduce TEWL. Sorbitol, |
| generations. | | | | sucrose, glucose, and other sugars are also |
| The majority of creams and lotions are emulsions. | | | | commonly used to hydrate the skin. Aloe, which |
| An emulsion can be defined simply as two | | | | contains a mixture of polysaccharides, |
| immiscible fluids in which one liquid is dispersed as | | | | carbohydrates, and minerals, is an excellent |
| fine droplets in the other. Homogenized milk is an | | | | moisturizer. As skin becomes drier in the winter |
| example of a typical oil-in-water (o/w) emulsion. | | | | months, it may be necessary to incorporate |
| Milk fat (oil) is dispersed in water as fine droplets | | | | materials that better seal the moisture in the skin. |
| by the homogenization process. The reason the | | | | Waxes are composed primarily of long-chain |
| fat does not float to the top immediately is due | | | | esters that are solid at room temperature. Some |
| to the presence of emulsifiers; in this case, a milk | | | | common waxes used in cosmetics are beeswax, |
| protein called sodium caseinate as well as several | | | | candelilla, carnauba, polyethylene, and paraffin. The |
| phopholipids. In the case of water-in-oil (w/o) | | | | melting points of waxes vary widely depending on |
| emulsions, water is dispersed as droplets and | | | | their unique composition and chain lengths. |
| suspended in the oil phase. The nondispersed liquid | | | | Commonly used in lip balms and sticks, waxes |
| or external suspending phase is also called the | | | | function as structuring agents, giving the stick |
| continuous phase. Mayonnaise, vinegar water | | | | enough rigidity to stand up on its own, as well as |
| dispersed as fine droplets in a continuous phase of | | | | barrier properties. By combining waxes with |
| soybean oil, is an example of a water-in-oil | | | | different properties such as high shine, flexibility, |
| emulsion. Lecithin from eggs stabilizes the | | | | and brittleness, optimal cosmetic performance can |
| mayonnaise emulsion. | | | | be achieved. Often waxes are combined with |
| Most emulsifiers can be considered surfactants or | | | | compatible oils to achieve the desired softness. |
| surface-active agents. These materials are able to | | | | Compatibility is generally determined by gauging |
| reduce the surface tension of water. What | | | | the turbidity and degree of separation of two |
| makes an emulsifier surface active is related to | | | | materials mixed together above their melt points. |
| its HLB, or hydrophile-lipophile balance. HLB is | | | | Waxes are particularly useful in hand creams and |
| determined by the size of the hydrophilic | | | | mascara emulsions for their thickening and |
| (water-loving or polar) portion of a molecule as | | | | waterproofing properties. |
| compared to the size of the lipophilic (oilloving or | | | | By incorporating enough wax into a thin lotion, a |
| nonpolar) portion. The HLB system was created | | | | thick cream can be formed. Many thickeners are |
| to rank the relative polarity of materials. The | | | | polymers. Cellulose, a fine powder polymer of |
| most polar, water soluble, materials are at the top | | | | repeating D-glucose units, swells in hot water |
| of the twenty-point scale with more non-polar, oil | | | | creating a gel network. Carbopol, a polyacrylic |
| soluble, materials closer to zero. The HLB of | | | | acid, swells when neutralized. Bentone clays swell |
| sodium caseinate is assigned a value of around | | | | when their structure, resembling a stack of cards, |
| fourteen because of its high solubility in water. | | | | is opened up through mechanical shear. |
| Lecithin, being poorly soluble in water, has an HLB | | | | Carrageenan, pectin, and locust bean gum are all |
| value of about six. Both have polar groups. The | | | | examples of cosmetic thickeners that are also |
| polar group in the milk protein is sodium. Lecithin's | | | | used in some of our favorite foods such as jellies, |
| surface-active component is a molecule called | | | | salad dressings, and pie fillings. Materials that work |
| phosphotidylcholine or PC. The polar, or water | | | | physiologically within the skin or aid in protecting |
| soluble part of PC is the phosphate functional | | | | the skin from insult are also called active |
| group. The emulsifiers' polar groups orient toward | | | | ingredients. The term "cosmeceuticals" coined by |
| the polar water phase. Their lipophilic, nonpolar | | | | famed dermatologist Dr. Albert Kligman, refers to |
| groups oriented toward the oil phase to form | | | | a product that is in-between a cosmetic and a |
| micelles. These spherical structures provide | | | | drug. Although a cosmetic, by legal definition, can |
| stability to the emulsion through Hydrogen bonding | | | | only serve to beautify and protect the surface of |
| and weak electrical forces. | | | | the skin, many cosmetic products can be shown |
| Skin-care emulsifiers can be divided into two | | | | to penetrate the dermal layers of the skin to |
| groups based on ionic charge. Materials that can | | | | exact a physiological change. |
| dissociate into charged species are considered | | | | Fruit acids are an example of an active material. |
| ionic while those that do not are called nonionic. | | | | Also called alpha hydroxyacids or AHAs, they |
| Ionic emulsifiers can be further classified by type | | | | have the ability to penetrate the skin, where they |
| of charge. Anionics are negatively charged when | | | | can increase the production of collagen, elastin, |
| solvated as in sodium stearate or soap. When | | | | and intracellular substances thus improving the |
| fatty acids are reacted with alkali they form | | | | appearance of the skin. Thousands of cosmetic |
| soaps. The process of soap formation is called | | | | actives are used to affect the skin in a variety of |
| saponification. The negatively charged stearic acid | | | | ways. They are used to lighten, tighten, and firm |
| group is the main emulsifying unit of the soap, | | | | the skin. They can be used to suppress |
| giving it the anionic classification. Positively charged | | | | perspiration as in the case of aluminum |
| emulsifiers are called cationic. Quarternium24's | | | | chlorohydrate. Salicylic acid and benzoyl peroxide |
| emulsifying unit dissociates into the positively | | | | are important ingredients because of their |
| charged ammonium group. Amphoterics are | | | | anti-acne activity. Some active materials are |
| compounds that express both negative and | | | | added to skin treatments to protect the skin |
| positive charges. | | | | from the environment. Dimethicone and |
| Nonionic emulsifiers are often used in skin-care | | | | petrolatum are examples of skin protectants. |
| emulsion for their safety and low reactivity. They | | | | Sunscreens are a class of compounds that |
| are generally classified by chemical similarity. | | | | protect the skin from ultraviolet radiation. |
| Glycerin, commonly added to cosmetic emulsions | | | | Wavelengths between 290nm and 400nm are |
| for its humectant properties, is the backbone of a | | | | particularly damaging to the skin. Sunscreens' |
| class of emulsifiers called Glyceryl esters. Glyceryl | | | | ability to absorb or reflect these damaging |
| monostearate, or GMS, is called a monoester | | | | wavelengths are rated by their SPF or |
| because of its sole ester linkage. The diester is | | | | sun-protection factor. For instance a person |
| prepared by esterifying two molecules of stearic | | | | protected with a factor-15 sunscreen will be able |
| acid for every molecule of glycerin. Glyceryl | | | | to stay in the sun fifteen times longer than if |
| mono- and diesters are very effective emulsifiers | | | | unprotected. Octyl methoxycinnamate, octyl |
| because they contain both polar hydroxyl (OH) | | | | salycilate, titanium dioxide, and avobenzone are |
| groups as well as non-polar fatty acids. If all three | | | | some important topical sunscreens. They can be |
| of Glycerin's hydroxyl groups are reacted, the | | | | classified as either UVA or UVB sunscreens |
| resulting triester will have little emulsifying | | | | depending upon the wavelengths they absorb. |
| capability. Stearic acid is called C18 fatty acid. The | | | | Benzophenone 4, a water-soluble UV filter, is |
| fatty acids, present in fats and oils, are classified | | | | commonly used to protect the color of cosmetic |
| according to their carbon-chain lengths. Because | | | | products. |
| stearic acid is a major component of many of the | | | | Pigments and dyes are used in products to impart |
| fats and oils used in beauty treatments, | | | | a color. Titanium dioxide (TiO2) is a white pigment |
| stearate-based emulsifiers are particularly useful. | | | | that is mined. In combination with natural mined |
| Fatty acids are key components of many | | | | and synthetic iron oxides, which range in color |
| cosmetic emulsifiers due their miscibility in a | | | | from red, yellow, black and brown, depending |
| variety of natural and synthetic oils. | | | | upon the degree of oxidation and hydration, a |
| Esters polyethylene glycol or ethylene glycol is | | | | range of color can be produced that will be |
| called PEG esters. A PEG ester's solubility is | | | | suitable for almost every skin tone. Face powders |
| determined by the number of PEG molecules | | | | are produced by blending inorganic oxides and |
| reacted per molecule of acid. PEG 6 oleate for | | | | fillers. Fillers are inert, generally inexpensive |
| instance has six molecules of PEG reacted with | | | | materials such as kaolin, talc, silica, and mica that |
| one molecule of oleic acid. As the number of | | | | are used to extend and fully develop colors. |
| polar, PEG molecules per acid molecule increases | | | | Pressed powders like eye shadows and blushers |
| the water solubility/HLB is increased; PEG 8 oleate | | | | are prepared by blending additional binding |
| is more soluble than PEG 6 oleate. The cosmetic | | | | ingredients such as oils and zinc stearate and |
| chemist will often use blends of glyceryl esters | | | | pressing the mixture into pans. |
| and a PEG ester with high and low HLB values to | | | | Eye shadows and lipsticks often contain |
| determine the required polarity to emulsify various | | | | pearlescent pigments commonly called pearls. |
| fats and oils. The many types of emulsifiers are | | | | Pearls sparkle and reflect light to produce a |
| too numerous to list, however McCutcheon's | | | | multitude of colors. They are prepared by |
| Emulsifiers and Detergents is an excellent source | | | | precipitating a thin layer of color on thin platelets |
| for a more complete listing. | | | | of mica. Varying the thickness of the color |
| The majority of emollients used in personal care | | | | deposited changes the angle of light refracted |
| and beauty items are fats and oils, also called | | | | though the composite, creating different colors. |
| lipids. Animal fat or tallow is composed primarily of | | | | Organic pigments are used to color lipsticks and |
| stearic and palmitic acids with carbon chains | | | | eye shadows. When organics are precipitated on a |
| lengths of 18 and 16 respectively. Many of the | | | | substrate they are called lake pigments. The term |
| major cosmetic companies are moving away | | | | lake refers to the laking or precipitating of the |
| from animal-based materials like tallow to | | | | organic salt onto a metal substrate such as |
| renewable vegetable-based materials. Coconut oil | | | | aluminum, calcium, or barium. They are called |
| and palm kernel oil are often used. Some of the | | | | D&C (drug and cosmetic) and FD&C |
| key characteristics required in good emollients are | | | | (food, drug and cosmetic) colors. Dyes are useful |
| good spreading properties, low toxicity/skin | | | | in providing tints for lotions, oils, and shampoos. |
| irritation and good oxidative stability. Oleic acid, a | | | | Most cosmetic products require the addition of |
| major constituent of olive oil has poor oxidative | | | | preservative to prevent microbial contamination |
| stability due to the presence of its double bond. | | | | and rancidity. Parabens and ester of parabenzoic |
| Fats and oils are considered saturated if they do | | | | acid are by far the most commonly used because |
| not have double bonds. Unsaturated oils like olive | | | | of their effectiveness against gram-positive |
| oil have double bonds that can react with oxygen, | | | | bacteria. Phenoxyethanol is used to protect |
| especially when heated. The oxidation process can | | | | against gram-negative strains. The cosmetic |
| produce off colors and odors in lipids causing them | | | | chemist will generally employ a mixture of |
| to go rancid and unusable. | | | | preservatives to protect against different bacterial |
| Petroleum-based emollients such as petroleum | | | | strains as well as yeasts and molds. Antioxidants |
| jelly and mineral oil are found in many formulations | | | | such as tocopherol (vitamin E) and BHT are also |
| because they do not contain double bonds or | | | | added to prevent oxidation of sensitive ingredients |
| reactive functional groups. Silicone oils such as | | | | as well as protect the skin from free-radical |
| cyclomethicone, dimethicone are often added to | | | | damage. |
| increase slip and emolliency. Oils that contain high | | | | |