chapter 1 the nature of skin Most people unconsciously treat their skin as a high-tech fabric--silky yet waterproof, glowing yet warm, silky and sexy yet resilient. The fabric benefits from regular laundering in the shower, occasional dry cleaning in a salon, and some ironing before special occasions. Many people believe that the luxurious fabric we are born in should always be spotless and fresh, no matter what it takes. We would rather bake in a tanning booth and add a glazing of shimmery lotion to hide imperfections than scrub our assets with sea salt and self-massage with virgin olive oil. We use ''mattifying'' lotions when our skin gets oily, hydrating creams when our skin feels dry, and battle blemishes when they become red, swollen, and very visible. When it comes to skin care, we tend to be reactive rather than proactive. Whenever possible, we opt for quick results and convenience. We are so busy fighting the consequences of the skin''s imbalance that no one remembers how it feels to have normal skin.

Normal skin does not exist anymore. Cosmetic companies invented ''combination oily,'' ''combination dry,'' and ''dehydrated oily'' skin types that require complex regimens and dozens of bottles to make skin look healthy and normal. However, a slight dryness and shiny T-zone are perfectly normal, no matter how hard the industry tries to convince us that we need to address these issues. We are so obsessed with all the new lotions and potions that promise to make our skin appear healthy that we don''t try to make it truly healthy. We are so eager to make these magic concoctions work that we do not ask ourselves whether this chemical cocktail is actually making our skin younger or any healthier. ''Healthy skin isn''t a quick fix,'' says Susan West Kurz, a holistic skin care expert and the president of Dr. Hauschka Skin Care. ''If you apply a cortisone cream, the blemish will go away, but the problem still exists within the system.

'' To support the normal functioning of your skin and naturally maintain its youthful looks, you need to first know how skin works. Our skin is an incredibly large and complex organ. The average square inch of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes (pigment skin cells), and more than a thousand nerve endings. Being only 2 millimeters thick, skin does a great job protecting us from the outside world, keeping a constant body temperature, absorbing the sun''s energy and converting it into vitamins while shielding us from UV radiation, storing fats and water, getting rid of waste, and sending sensations. Skin is made up of three main layers: an epidermis, with the important top layer, stratum corneum (''horny layer''), and a dermis. Every layer of the skin works in harmony with the others. The skin is constantly renewing itself, and anything that throws its functions off balance affects all skin layers at the same time. For most people, proper skin care starts with adequate hydration.

But as shocking as it sounds, healthy skin doesn''t really need any additional moisture. Our skin is perfectly able to keep itself hydrated. Its surface is kept soft and moist by sebum and a natural moisturizing factor (NMF). Sebum, a clear waxy substance made of lipids, acts as a natural emollient and barrier. It helps protect and waterproof hair and skin and keep them from becoming dry and cracked. It can also inhibit the growth of microorganisms on the skin. Sebum, which in Latin means ''fat'' or ''tallow,'' is made of wax esters, triglycerides, fatty acids, and squalene. The amount of sebum we produce varies from season to season and can be predetermined genetically, but in fact, the amount of sebum needed to keep skin moist and healthy is very small.

People who are ''blessed'' with oily skin think their skin is dripping oil, but they produce only 2 grams of sebum a year! For some reason, sebum became public enemy number one in the fight for clearer skin. It is just as absurd as saying that tears should be blamed for smudged mascara! Skin experts claim that sebum combines with dead skin cells and bacteria to form small plugs in the skin''s pores. The only way to keep skin clean, they insist, is to completely stop the production of sebum. Instead of promoting good skin care habits that would eliminate dead skin cells and bacteria buildup, these ''experts'' recommend stripping skin of its vital fluid with the drug isotretinoin or ''deep'' cleansers that wreak havoc on the skin''s nature-given abilities to cleanse and revitalize itself through cellular turnover and natural moisturizing. Sometimes your skin may feel tight and scaly. This is when your skin''s oil barrier loses its effectiveness, most often due to a cold and dry environment during the winter. Instead of letting skin readjust itself by producing more sebum, we cover it with a synthetic, oily film that physically blocks water loss. On top of this film, we may put an additional layer of waxes, petrochemicals, talc, and dyes in the form of makeup.

To remove this airtight layer cake, we treat our skin with ionic surfactants and detergents that destroy the natural moisturizing factor, leaving the skin more vulnerable than before. Squeaky-clean is good for kitchen sinks, but not for human skin! While sebum locks moisture in skin, the natural moisturizing factor (NMF) keeps skin hydrated. NMF is a mixture of water, free amino acids, lactic acid, and urea, as well as sodium, potassium, chloride, phosphate, calcium, and magnesium salts that keep the skin moist and supple by attracting and holding water. The water content of the skin''s outer layer is normally about 30 percent; it rises after the skin has been treated with certain humectants, such as hyaluronic acid, that boost the skin''s ability to retain moisture. To help preserve water, skin cells contain fats and fatty acids, which trap water molecules and provide a waterproof barrier that prevents transepidermal water loss (TEWL). TEWL is the constant movement of water through the epidermis. Water evaporates through the epidermis to the surrounding atmosphere. Environmental factors such as humidity, temperature, season, and the moisture content of the skin can all affect TEWL.

Our skin gets drier as we get older because it loses some of its intercellular lipids after age forty. It is important to feed aging skin with substances that resemble the skin''s own oils. These moisturizers should become oilier, but not necessarily heavier, as our skin ages. Essential fatty acids can greatly help skin retain moisture, and since they are natural, our skin accepts them more happily, which means less irritation. Advocates of synthetic skin care insist that our skin is virtually watertight. Many say skin can be scrubbed, steamed, and washed, and nothing penetrates it deep enough to cause any damage. At the same time, many conventional cosmetics claim they deliver collagen, vitamins, and minerals to feed our skin. So do cosmetics really ''get under our skin''? In fact, beauty is skin deep.

Human skin is a powerful absorption organ that seems to be constantly hungry for anything that touches its surface. Just like a curious toddler, our skin grabs every available molecule, every single drop of water, every lick of makeup, and every whiff of fragrance and takes it to its cellular ''mouth'' to taste, chew on, and, most likely, ingest. Oxygen, nitrogen, and carbon dioxide, as well as toxic pollutants, enter our skin via three doors: sweat ducts, hair follicles and sebaceous glands, or directly across the stratum corneum. This ability of skin to absorb chemical substances so they can be spread throughout the body is widely used in medicine. Transdermal delivery drugs for motion sickness, cardiovascular disease, chronic pain, smoking cessation, and birth control are already widely used. According to new estimates, our skin can absorb up to 60 percent of substances applied to its surface. Unfortunately, along with water, vitamins, minerals, and oxygen, skin soaks up potentially carcinogenic ingredients that increase our risk of having cancer at some point in our lives--as if breathing polluted air and eating chemicals was not enough! To perform their magic, many cosmetic products need to push active ingredients deeper beyond the stratum corneum, the uppermost layer of skin comprised of dead skin cells. Traditionally, it was thought that hydrophilic (water bonding, or dissolvable in water rather than oil) chemicals do not penetrate deep into skin, while lipophilic chemicals (oils or oil-in-water emulsions) diffuse deeper inside the dermis.

Today, scientists know that the process is much more complicated. Various substances can penetrate the skin using different vehicles, sometimes as simple as water. This is when penetration enhancers, also called sorption promoters or accelerants, come into play. To deliver active ingredients, they decrease the resistance of skin''s barrier. Some dissolve intercellular matrix, some change the skin''s metabolism, and some ­damage or alter the physical and chemical nature of the top skin layer. Most common penetration enhancers include alcohols (ethanol), glycols (propylene glycol), and surfactants. Liposomes, biomolecular spheres that encapsulate various chemicals from drugs to active components of cosmetic products, also serve as penetration enhancers. The most common liposome is phosphatidylcholine from soybean or egg yolk, sometimes with added cholesterol.

Nanoparticles, currently used to deliver sunscreens and vitamins A and E, can boost the skin''s permeability by up to 30 percent. Some penetration enhancers, such as transferomes, which are made of surfactants and ethanol, are able to deliver up to 100 perc.