Putting on a good face – the chemistry of cosmeticsThe pursuit of beauty has spawned a massive industry founded on the science of chemistry - the cosmetics industry. Key text Key textThe use of cosmetics is not a modern phenomenon. Ancient Egyptian women used kohl to darken their eyelids, and Cleopatra is said to have bathed in milk to whiten and soften her skin. More than 3000 years ago Greek women used poisonous lead carbonate to achieve a pale complexion, costing some wearers their lives. Today, cosmetics are big business. According to the Australian Bureau of Statistics, Australians spent A$4.1 billion on cosmetics, perfumes and toiletries in 1998-99. Cosmetic advertising is now targeting a wider audience than ever. Most of us – males and females – care about our appearance. What is a cosmetic?
The Australian Trade Practices Act 1974 defines a cosmetic product as ‘a substance or preparation intended for placement in contact with any external part of the human body' (this includes the mouth and teeth). We use cosmetics to cleanse, perfume, protect and change the appearance of our bodies or to alter its odours. Products that claim to ‘modify a bodily process or prevent, diagnose, cure or alleviate any disease, ailment or defect’ are called therapeutics (Box 1, Ingredient labelling). This distinction means that shampoos and deodorants are placed in the category of cosmetics, while anti-dandruff shampoos and antiperspirants are considered to be therapeutics. What do cosmetics contain?
Most cosmetics contain a combination of at least some of the following ingredients: water, emulsifier, preservative, thickener, colour, fragrance and pH stabilisers. Emulsifiers
Many cosmetic products are based on emulsions – small droplets of oil dispersed in water or small droplets of water dispersed in oil. Since oil and water don't mix, emulsifiers are added to produce the small droplets and to prevent the oil and water phases from separating. Emulsifiers work by changing the surface tension between the water and the oil, thus producing a homogeneous product with an even texture. Preservatives
Preservatives are added to cosmetics to prevent the growth of microorganisms (eg, bacteria and fungi), which can spoil the product and possibly harm the user. Preservatives used in cosmetics can include parabens, benzyl alcohol and tetrasodium EDTA (ethylenediaminetetra-acetic acid). Thickeners
Thickening agents such as polymers are often added to cosmetics to change their consistency. Polymers can be synthetic (eg, polyethylene glycol) or derived from natural sources (eg, polysaccharides). Seaweeds are a common source of natural polysaccharides – carrageenans are extracted from red algae and alginates from brown algae. Cosmetics that are too thick can be diluted with solvents such as water or alcohol. Fragrances, colours and pH stabilisers
The ingredient list of a cosmetic product might also include chemicals that give a pleasant smell to the product, provide an appealing colour, or adjust the pH (the acidity). Some types of cosmetics and their ingredients
Moisturisers are generally used to treat dry, scaly skin. Our skin becomes dry when water is lost from the top layer of dead skin cells faster than moisture can enter it from the living layers of skin below (Box 2, Only skin deep?). Moisturisers can correct this problem in two ways: by preventing further moisture loss (occlusion) and by adding substances that increase the water-holding capacity of the skin (humectants). Occlusive moisturisers may contain oils such as isopropyl palmitate, stearyl alcohol or light mineral oil. The oils form a waterproof layer on the skin, reducing evaporation and allowing the body’s natural process of rehydration to return the skin to a normal water level. Humectant moisturisers may contain substances like glycerine or alpha hydroxy acids (fruit acids such as glycolic acid, citric acid or lactic acid), which add water to the top layer of skin.
Water solubility - or the lack thereof - is an important factor in creating lipstick. Lipsticks are generally made by combining a water-insoluble dye with wax and a non-volatile oil (beeswax with castor oil is a common formulation). This results in a substance that is stiff, but will spread easily on your lips. Because it’s water-insoluble, the lipstick won’t be dissolved by saliva or by the drink you’re sipping. Some lipsticks also use dyes which react with the amino acids in the protein of your skin - this is why some lipsticks appear blue or green in the tube, but turn a deep shade of red when applied to your lips. Fake tans also change colour on contact with skin. The active ingredient in most fake tans is dihydroxyacetone, a colourless compound that darkens when it reacts with the amino acids in the top layer of skin. The colour change is permanent, but because skin cells are constantly being shed the tan is usually gone after about a week. Some unintended effects of chemicals found in cosmetics
Unfortunately, sometimes the ingredients in cosmetics can have unintended side-effects. For example, skin allergies (allergic dermatitis) to specific ingredients can be a problem. Allergies to cosmetic products can be due to chemicals such as added fragrances and preservatives. This can lead to a skin rash where the product is applied. If you think you may be allergic to a cosmetic product, it is important to determine which ingredients may be causing the problem. A specialised allergy test, called a patch test, may be helpful in this. Chemicals causing the allergy can then be avoided by reading product labels. Other people, while not allergic to a specific ingredient, may nevertheless find that a product irritates their skin because it damages the outer layers - a condition known as irritant dermatitis. Exfoliants and skin peels leave the skin underneath temporarily more vulnerable to sun exposure because they remove the outermost protective layer of dead skin cells. Over-washing of hair or skin with soaps and detergents can strip the skin’s natural protective oily layer, resulting in dry and scaly skin. Alternatively, excessive use of make-up or oily moisturisers can block pores and aggravate acne.
In our pursuit of beauty, it is wise to remember that cosmetics can be complex combinations of chemicals. Reading the label and understanding which ingredients are used in a product are helpful when putting on your best face.
Box 1. Ingredient labellingLike the food industry, the cosmetics industry is subject to mandatory labelling requirements by Australian government regulations. Product ingredients must be listed on the packaging, on the product itself, or shown in some other way that allows the consumer to be informed. As with food labels, ingredients are listed in descending order by mass or volume. The purpose of this mandatory labelling is to allow consumers to identify ingredients they might be allergic to, and to compare the ingredients in products claiming to have similar benefits. Products are classified as therapeutic goods rather than cosmetics when they claim to treat an ailment or modify a bodily process. Therapeutic goods are subject to different labelling requirements. Unlike cosmetics, they are required to show only their active ingredients and any ingredients known to have the potential to cause adverse affects in some people. Antiperspirants and anti-dandruff shampoos fall into this category. Cosmetic products are not required to demonstrate their effects scientifically in the same way that therapeutic products are. Their claimed effects are usually couched in cautious language such as ‘may reduce the appearance of fine lines and wrinkles’. So consumers should be aware that many of the claims made for cosmetic products have not been scientifically proven to be true. Related sites
Box 2. Only skin deep?Our skin is our boundary with the outside world. With protective, regulatory and sensory roles, the skin is far more than just a covering to the body. It is more complex than a quick look at its surface suggests. Like all other body organs it is make up of numerous cells in various tissues that are organised together to perform its functions. It is the body’s largest organ, comprising about 12 per cent of the total body weight. The skin helps the body regulate the correct fluid balance by reducing water loss through its surface and preventing the absorption of too much water during baths or swimming. It helps the regulation of temperature – fatty tissues conserve heat, and the sweat glands cool the body surface when necessary. Variation in blood supply to its surface also regulates the amount of heat lost. Skin also helps with the disposal of waste products, especially through the sweat glands. It is involved in the synthesis of vitamin D and the metabolism of some hormones. The skin has several important sensory functions, particularly the detection of contact and heat. The layers of the skin
Human skin consists of two distinct layers – the epidermis (on the outside) and the dermis. The epidermis is made up of several layers of cells The epidermis consists of layers of cells. Old cells are continuously shed or worn away from the surface and replaced by new cells generated by the cube-shaped cells of the basal layer. Newly formed epidermal cells move upwards through the middle layers until they reach the outermost layer, from which they are eventually shed. As the cells migrate, they mature and become filled with a tough protein, keratin. Finally they compact to form the flat keratin plates that make up the skin’s surface. Melanocytes are specialised pigment-producing cells in the basal layer of the epidermis. Their long ‘arms’ extend between the cells of the epidermis. They produce melanin, which is the protein responsible for skin colour. Melanocytes inject melanin into the surrounding epidermal cells, which then carry the pigment upwards to the surface as they mature. All humans, fair and dark, have about the same number of melanocytes but the rate of pigment production varies enormously. The amount of melanin produced is in part determined genetically, but it also increases in response to exposure to sunlight. In darker skin, pigment is produced much faster and in greater amounts than in fair skin. If melanin is produced unevenly freckles form. The dermis layer contains various important structures The dermis consists largely of supportive tissue, but it also contains important structures like hair follicles, sweat glands and sense organs. The supportive tissue, which is a network of protein fibres embedded in a jelly-like substance, gives the skin its strength, elasticity and resilience. The protein fibres and the jelly-like substance are produced by special cells, the fibroblasts, that are scattered through the dermis. The hair grows in follicles in the dermis. Hair itself is a roughly cylindrical strand of dead cells. It grows from the bottom of the follicle tube. Each hair has a small muscle that pulls it from its normal slanting position to a more erect one and gives us the feeling that ‘our hair is standing on end’ when we are frightened or cold. Sweat glands also originate in the dermis and open to the surface of the epidermis. Each gland consists of a coiled narrow tube with a long duct to the surface. In releasing sweat to the surface, where it cools the skin by evaporation, sweat glands perform an important heat regulatory function. The nerve fibres of the skin also form finely branching networks just
below the epidermis. Some of the nerve fibres are specially adapted to
carry sensation such as touch, heat, cold and pain. Areas of sensitive
skin such as the fingertips contain large numbers of these specialised
nerve endings. Related sites
Activities
Further reading
Australasian Science April 2002, pages 28-29 Magic molecular mortar (by Miles Page) Looks at how detergents (a common cosmetic ingredient) work at the molecular level.
Cosmos Feb-Mar 2008, pages 64-69 Science skin-deep (by Elizabeth Finkel) Looks at ‘cosmeceuticals’ – a new generation of products that remove wrinkles.
New Scientist 24 January 2004, page 11 Are deodorants safe? (by Jo Whelan) A report on studies assessing the link between deodorants and breast cancer.
17 January 2004, pages 40-41 The best skin cream you ever wore (by Sylvia Pagàn Westphal) Looks at the moisturising and protecting properties of newborn babies’ vernix and how scientists are attempting to recreate it in laboratories.
21 April 2001, pages 34-37 The perfume hunters (by Stephanie Pain) Explains how fragrances are ‘caught’ and developed into new scents for consumer products.
Scientific American April 2002, pages 58-65 The science of bad breath (by Mel Rosenberg) Looks at the condition of bad breath, what causes it and what can be done to treat it.
Useful sitesCosmetics (US Food and Drug Administration)
Information for consumers and industry covering a wide range of topics such as ingredients, labelling and cosmetic questions and answers. Includes links to special features for kids and teens.
Wrinkle free zone (Australian Broadcasting Corporation – Online Feature)
Of all the skin care products you can slap on your face, anti-wrinkle creams are the ones that will hit your pocket the hardest. But believe it or not there's a reason behind the cost. Heather Catchpole looks into the nanotechnology of keeping skin younger-looking longer.
Cosmetics and toiletries – ingredient labelling (Australian Competition and Consumer Commission)
This product safety guide explains the Australian government mandatory information standard that applies to labelling of cosmetics and toiletries. It includes which products are covered by the standard, the responsibilities of suppliers and retailers and the ACCC's role in enforcing compliance to the standard.
Royal Society of Chemistry (UK)
Skin deep (Environmental Working Group, USA)
A safety assessment of ingredients in personal care products.
Know your skin, hair and nails (Mayo Clinic, USA)
Learn about the anatomy of these structures, how they function and how they affect your health.
Personal care products: myths, rumours and facts (Australian Consumers' Association)
Assesses claims made against cosmetic ingredients by looking at the available facts.
Australasian Society of Clinical Immunology and Allergy
Solving problems related to the use of cosmetics & skin care products (American Academy of Dermatology)
Brochure that aims to identify possible problems with consumer products and suggest solutions.
You've come a long way baby: a history of cosmetic lead toxicity (Clinics in Dermatology, July-August 2001, USA)
Review article that gives a good summary of how lead has been used in cosmetics through different periods of history.
Cosmetic ingredients (DERMAdoctor.com, USA)
Article with information about common cosmetic ingredients. Includes a listing of common ingredients and their function.
Specific cosmetic products:
Glossaryactive ingredient. The ingredient that is responsible for producing the desired effect of a mixture of ingredients and for giving the product its main characteristic. The active ingredient is not necessarily the most common ingredient in a product. amino acid. The basic building block of protein. All amino acids contain an amino (NH2 ) end, a carboxyl end (COOH) and a side group (R). In proteins, amino acids are joined together when the NH2 group of one forms a bond with the COOH group of the adjacent amino acid. The side group is what distinguishes each of the amino acids from the others. There are 20 common amino acids: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. carcinogen. A substance that is known to cause cancer. humectant. A substance that can absorb water from moist surroundings. hydrophilic. Describes a substance that absorbs, dissolves in or is attracted to water. lead carbonate. A naturally occurring white amorphous powder with a chemical formula of PbCO3. Used in exterior paints, ceramics, cements, processing of parchment and as a laboratory reagent. lipophilic. Describes a substance that dissolves in or is attracted to fats, oils or other lipids. Lipophilic functional groups or molecules prefer to be in an environment where there is no water. occlusion. The act of closing, shutting or stopping up. In cosmetics this usually refers to a shield or film that is spread onto the skin to slow or prevent moisture evaporation. This shield or film is usually made up of materials, such as oils and waxes that cannot be penetrated by water. patch test. Test used to identify allergies due to chemicals coming in contact with skin. Individual chemicals are applied separately to the skin and then the skin is observed for reactions over a few days. For more information see Patch testing (dermatology.co.uk). pH. The pH scale is used to measure the strength of acids and bases (or alkalis). The acid strength in the human stomach is about pH 2. Alkalis such as caustic soda and basic household cleaners have a pH of about 12 to 14. Neutral is pH 7, (ie, neither acidic or alkaline). The scale is logarithmic, so pH 4 is ten times as acidic as pH 5 and pH 2 is ten times as acidic as pH 3, and so on. For more information see About soil pH (National Aeronautics and Space Administration, USA). polymer. Polymers are large molecules that are made up of many units (monomers) linked together in a chain. There are naturally occurring polymers (eg, starch and DNA) and synthetic polymers (eg, nylon and silicone). More information can be found at The basics – polymer definition and properties (Plastic Resource, USA), Introduction to polymers (Case Western Reserve University, USA) and History of polymers and plastics for teachers (Hands On Plastics, American Plastics Council). polysaccharide. A carbohydrate made up of a long chain of simple sugar molecules joined together. Starch and cellulose are examples of polysaccharides. skin allergy. An allergy is a hypersensitivity to substances in the environment which do not bother most people. Allergy to cosmetics usually manifests as a rash on the skin where the product has been applied. This condition is known as allergic contact dermatitis, and is often due to fragrances and preservatives in the cosmetic product. For more information see Allergic contact dermatitis (New Zealand Dermatological Society). surface tension. A property of liquid surfaces that causes the surface layer to behave like a thin elastic 'skin'. Molecules in a liquid have attractive forces that hold them together. Molecules on the surface are attracted to molecules from all sides and below, but not from above. This results in a downward and sideways pull on molecules on the surface layer. For more information see Surface tension (Georgia State University, USA). External sites are not endorsed by the Australian Academy of Science. The Australian Foundation for Science is also a supporter of Nova. © Australian Academy of Science |