Dermatologists are frequently queried by patients regarding moisturizer selection. The fact that no one moisturizer meets the need of all patients is clearly illustrated by the tremendous variety of products available for purchase through a variety of vendors, including drug stores, mass merchandisers, cosmetic counters, spas, boutiques, and internet sales. Indeed, the moisturizer market is confusing for patients and physicians alike. One of the more common areas of controversy is whether patients should select an oil-free or an oil-containing moisturizer. Some manufacturers advertise that their products are entirely oil-free. Does this confer some benefit? Acne patients swear that if they use anything with oil, it causes them to breakout. Does oil in moisturizers cause acne? Others state that they never use anything with petrolatum because it is not natural. Is there any truth to any of these ideas from a medical standpoint? Or, are patients and physicians falling prey to the power of advertising and the promise of beauty?
The main ingredient used in oil-containing formulations is petrolatum and the main ingredient in oil-free formulations is dimethicone. These two ingredients will be discussed as prototypes in the oil vs. oil-free debate.
The most important oil in dermatology is petrolatum. It is an age old chemical originally manufactured and patented by Robert A. Chesebrough in 1872. He called his new discovery “Vaseline,” a name and product that are still in existence today. Chesebrough originally recommended petrolatum as a chemical to treat leather, however, its value was soon recognized as a remedy for skin ailments. Petrolatum first appeared in the US Pharmacopoeia in 1880.
Petrolatum is a semisolid mixture of hydrocarbons obtained through the dewaxing of heavy mineral oils. Pure cosmetic grade petrolatum is odorless and tasteless. It does not bind proteins or undergo chemical alteration in the skin accounting for the fact that is not allergenic or a cutaneous irritant. In fact, petrolatum is used as the negative control for patch testing by many dermatologists and can be found as a carrier for many of the ingredients on the dermatologist’s standard patch test tray.
Petrolatum is also noncomedogenic. It is a hydrocarbon and can easily contain impurities, if not well manufactured. Poor quality petrolatum may indeed contain tar impurities and tar is a known comedogen, however, cosmetic grade petrolatum is devoid of tar impurities and does not cause comedone formation. Perhaps some of the confusion regarding the comedogenicity of petrolatum is due to the comedogenicity of the impurities.
No cosmetic ingredient can come close to the ability of petrolatum to reduce transepidermal water loss by 99%, thus creating an environment conducive for skin healing. Petrolatum can also intercalate into the intercellular corneocytes spaces temporarily mimicking the intercellular lipids and reducing itching and skin roughness. No one has synthetically duplicated petrolatum, which is found in about 75% of the skin care products and cosmetics marketed today.
All oil-free skin care products and cosmetics must have an oily substance to allow the formulation to function as intended on the skin. The common oil used in all oil-free formulations is silicone oil. Silicone was developed in the 1930s when Franklin, Hyde, and McGragor discovered a method of extracting pure silica from raw quartzite and converting it to dimethyl silicone. There are currently over 4200 silicone-based products used in industries ranging from medicine to transportation to paper manufacture to food production to skin care.
Silicone originates from silica, which is found in sand, quartz, and granite. It derives its properties from the alternating silica and oxygen bonds, known as siloxane bonds, which are exceedingly strong. These strong bonds account for the tremendous thermal and oxidizing stability of silicone. Silicone is resistant to decomposition from ultraviolet radiation, acids, alkalis, ozone, and electrical discharges. The silicone used in topical preparations is odorless, colorless, nontoxic oily liquid. To date, there are no reports of toxicity from topical silicone use.
The most common silicone used in skin care and cosmetics is dimethicone. Dimethicone is a clear liquid that is water-insoluble and can be used in place of petrolatum and mineral oil in formulations. Dimethicone is found in all oil-free moisturizers and facial foundations. It is hypoallergenic, noncomedogenic, and nonacnegenic. This is the reason why it is popular among persons with sensitive skin and acne.
The data has been presented for both oil formulations, containing petrolatum, and oil-free formulations, containing dimethicone. Which formulations are better? Both ingredients are hypoallergenic, noncomedogenic, nonacnegenic. The answer is that they are both good and will provide superior functioning, but the best formulation for a given patient depends on the skin needs of the individual.
Oil-based formulations are superior in dry skin. Petrolatum reduces transepidermal water loss much better than dimethicone. Petrolatum is also longer-lived on the skin surface and can temporarily replace the intercellular lipids. Dimethicone cannot function in this manner. However, petrolatum creates a warm heavy feeling on the skin surface and can be greasy. Dimethicone is less occlusive and is termed an astringent emollient because it can decrease the stickiness of petrolatum-based formulations. Dimethicone is excellent at making the skin surface smooth and shiny without leaving behind an objectionable film.
Oil-free formulations with dimethicone perform superiorly in persons with oily skin. The dimethicone can mix with the sebum to make the face feel less oily. Dimethicone is also excellent at smoothing the dry skin associated with acne medications while not making the skin feel greasy. This too is an important characteristic for oily skin products. Dimethicone does not create an optimal environment for healing, but then oily skin does not necessarily demonstrate barrier damage.
The oil versus oil-free debate should be considered separately from marketing jargon. Both types of formulations have a place in dermatology. In general, oil-based formulations are preferred where barrier defects exist while oil-free is better when sebum production is abundant.
The tremendous variety of moisturizers in the marketplace today makes product selection bewildering for both the dermatologist and the patient. Each bottle examined appears more inviting than the next. Bottle A makes the skin smoother and more radiant while bottle B promises to minimize facial fine lines. What should the patient do who desires both smooth skin and wrinkle reduction? Does she need to buy both bottles? Of course, she also needs something to camouflage dyspigmentation and that new antioxidant ingredient X may be beneficial. One solution is to apply 4 moisturizers to the face to ensure that nothing is missed. However, 4 moisturizing preparations applied to the facial skin simultaneously might produce a strange smelling sticky goo. What is the solution to this dilemma?
It is critical to recognize that while the many moisturizers available for purchase differ subtly, there are some basic functions that moisturizers provide which can be easily organized into 4 categories. These categories are summarized in Table 1, forming a hierarchical organization for moisturizing products. I have termed it a hierarchical organization because it lists the properties of moisturizers from basic to most complex, least expensive to most expensive, unsophisticated to sophisticated in terms of formulation, and oldest to newest. A discussion of this hierarchy should help better unravel confusion in the moisturizer market.
The most basic consumer need achieved by moisturizer application is smooth and soft skin. All moisturizers in the current marketplace make the skin smooth and soft. If you apply a sample of a moisturizing cream to the hand of a patient, their immediate inclination is to see how the product changes the tactile properties of the skin. Most dermatologists have been confronted by a drug company representative who wants to apply a new topical drug to the dermatologist’s hand. What can the dermatologist assess? Only the tactile qualities of the product.
Do the tactile properties of the moisturizer translate into better skin functioning? No. Smooth and soft is an assessment of the organization of the corneocytes on the skin surface. As the intercellular lipids are removed, the edges of the corneocytes fold creating an irregular skin surface. This irregular surface feels rough when stroked due to increased skin friction. Emollients, which are thin oily substances can deposit between the desquamating corneocytes and function like glue to stick the corneocyte back to the skin surface, decreasing friction and creating the soft, smooth skin feel desired by patients. Table 2 lists some of the commonly used emollients.
It is important to separate emolliency from moisturization. Emollients smooth down skin scale, not necessarily increasing the water content of the skin. Moisturizers that sell for less than $5 for a 16 ounce bottle are mainly emollients. Most moisturizers are emollients, but not all emollients are moisturizers. These ingredients are bifunctional. Usually, it is the concentration and number of ingredients that separates a moisturizer from an emollient. Lower priced moisturizers, which are typically lotions, contain water as the first ingredient. The water delivers the emollients to the skin surface and evaporates. This type of moisturizer is met with high consumer enthusiasm as it leaves the skin feeling smooth and soft without a greasy film, but these products may not optimally increase skin hydration. Patients that use this type of product will note that frequent application is required, since the emollient effect is temporary. Many of the high fragrance lotions marketed to women and teenagers are of this type.
Moisturizers that are medically relevant increase skin hydration and improve skin tactile characteristics. They contain the same ingredients listed in Table 2, but will contain a greater variety and in higher concentration. Products that increase skin hydration will leave behind a more noticeable film, since it is the film that creates an artificial barrier. Most moisturizers function by placing a water impermeable film over the skin surface that decreases evaporation of water from the skin to the lower humidity atmosphere. Moisturizers do not moisturize the skin. In the strictest sense, the word “moisturizer” is a misnomer, as moisturizers do not add water to the skin. Any water in a moisturizer formulation is a vehicle that evaporates, possibly drying the skin further, without enhancing skin water content. This explains why frequent application of moisturizers intended to function as emollients will further damage xerotic skin due to repeated wetting and drying of the skin surface.
Moisturizers that hydrate the skin function by decreasing transepidermal water loss, as mentioned previously, and by attracting water to the dehydrated stratum corneum and epidermis. Substances that reduce transepidermal water loss are oily occlusive substances, such as petrolatum, mineral oil, dimethicone, cyclomethicone, etc. Substances that attract water to the skin are known as humectants and include glycerin, sorbitol, propylene glycol, hyaluronic acid, sodium PCA, proteins, etc. The best moisturizers delivering skin hydration will contain both occlusive and humectant ingredients. The sum of these skin effects results in an environment optimal for barrier repair. In short, moisturizers do not moisturize the skin, but rather facilitate barrier repair by encouraging the natural restorative process.
Skin hydration can also result in decreased wrinkle depth, which creates the appearance of more youthful skin. Wrinkles of dehydration, most common around the eyes and upper cheeks, may benefit from the application of a moisturizer that contains occlusive and humectant ingredients. While wrinkle reduction may appear to be a functional benefit, it is a result of increased skin hydration that will be temporary unless skin barrier repair occurs.
Emolliency and skin hydration are two basic needs of a moisturizer, but improving the optical appearance of the skin is an additional requirement for products functioning in the appearance enhancement realm. The optical appearance of the skin can be enhanced by the methods presented in Table 3. With advancing age, the even distribution of melanin, hemoglobin, and collagen become more irregular. Products that can deliver a pigmented film to the skin surface or enhance light reflection from the skin surface may improve the optical appearance of the skin. Liquid, cream, and cream/powder facial foundations are moisturizers containing talc and iron oxide to camouflage the underlying skin and spread pigment particles evenly over the skin surface in addition to increasing skin hydration and leaving the skin smooth and soft.
Another strategy for optical skin improvement is to stain the corneocytes brown. This is the function of progressive self-tanning creams. These low concentration dihydroxyacetone (DHA) creams bind to the protein of the stratum corneum to create melanoidins that have a brown color. With each application, the depth of the brown color increases giving the skin a tanned appearance that camouflages underlying pigment irregularities. This brown color can be considered semi-permanent and will last for 1-2 weeks. The moisturizing vehicle increases skin hydration while delivering the DHA to the skin surface fulfilling multiple functions.
Finally, the appearance of the skin can also be improved by applying a film of light reflective particles to the skin surface. The most popular of these products are the moisturizing mineral makeups. These facial foundations have a high concentration of mica, which reflects light. Amongst the ground pigments are tiny spheres containing moisturizing ingredients to allow the powder to stick to the skin surface. These products provide minimal moisturization, but excellent emolliency and moderate skin camouflage.
The most sophisticated and expensive moisturizers deliver emolliency, moisturization, skin appearance improvement, and cosmeceutical ingredients to the skin surface. These are modern moisturizers with the ability to repair the skin barrier, increase skin hydration, and improve the functioning of the skin. The moisturizing vehicle serves as a carrier for active agents, transporting them to the skin surface. Once on the skin surface, the active agent must reach the proper skin destination in an active form with the ability to separate from the vehicle carrier. This is certainly a tall order for any skin care product. Do these products actually achieve their goal? Many of them are extremely well formulated moisturizers with cosmeceutical ingredients added to distinguish them from other products or to allow expanded marketing claims. This is the area in which growth will occur in the moisturizer market.
The delivery of cosmeceuticals and the claims that can be made are hampered by the current classification of cosmeceutical moisturizers as cosmetics in the United States. Japan has addressed this issue by creating a category of “quasi drugs.” Change is unlikely to be forthcoming in United States as more pressing issues of drug regulation remain before the FDA. Nevertheless, this is the moisturizer category to watch in the future.
The plethora of moisturizers in the marketplace can be categorized based on their ability to deliver a variety of skin benefits. These benefits can be summarized as smooth soft skin, increased skin hydration, optically enhanced skin, and cosmeceutical delivery. A modern moisturizer will deliver in each of these areas. By understanding the hierarchical functioning of moisturizers, it is possible to perhaps better examine the benefits of product use.
Petrolatum is an interesting substance with a rich dermatologic history. It is an age old chemical originally manufactured and patented by Robert A. Chesebrough in 1872. He called his new discovery “Vaseline,” a name and product that are still in existence today. Chesebrough originally recommended petrolatum as a chemical to treat leather, however, its value was soon recognized as a remedy for chapped hands and as a hair pomade. Later, petrolatum was adapted to the pharmaceutical industry as a vehicle instead of lard. It offered the benefit of preservative-free stability, due to its anhydrous nature. Lard based preparations, which were commonly used in topical formulations at the time, frequently turned rancid.
This article examines the utility and controversies concerning petrolatum in dermatologic preparations. Petrolatum has tremendous usefulness in dermatology, not only as a vehicle in prescription topical formulations, but also in over-the-counter drugs, wound healing agents, cosmeceuticals, and moisturizers.
Petrolatum is a semisolid mixture of hydrocarbons obtained through the dewaxing of heavy mineral oils. Pure cosmetic grade petrolatum is practically odorless and tasteless, however other hydrocarbon contaminants in lower quality petrolatum may account for a distinct chemical smell noted with some products. Petrolatum first appeared in the US Pharmacopoeia in 1880 and has been a widely used ingredient in skin care products and topical pharmaceuticals ever since. It is interesting to note that petrolatum has never been duplicated synthetically.
Petrolatum has many uses in industry and manufacturing, but its cutaneous benefit was first recognized by the American Pharmaceutical Association in 1875 for the treatment of burns. It was then used to moisturize the skin and hair in its pure form. Later, as cosmetic chemistry advanced, petrolatum was used as the base for a variety of hand and facial moisturizers to which color and fragrance were added. Petrolatum formed the basis of the first successful facial night cream that was marketed as “Mary Kay” cosmetics, a product still available today. Petrolatum then found its way into lipsticks, since it is an ideal base to mix with waxes and transfer pigment to the lips. In summary, petrolatum is an important ingredient in body lotions, moisturizing creams, shaving creams, body washes, antiperspirants, ethnic hair care products, and colored cosmetics.
Petrolatum is the most effective moisturizing ingredient on the market today, reducing transepidermal water loss by 99%. It functions as an occlusive to create an oily barrier through which water cannot pass. Thus, it maintains cutaneous water content until barrier repair can occur. Petrolatum is able to penetrate into the upper layers of the stratum corneum and aid in the restoration of the barrier which is initiated through the production of intercellular lipids. There are three intercellular lipids implicated in epidermal barrier function: sphingolipids, free sterols, and free fatty acids. It has been established that these lipids are necessary for barrier function, since solvent extraction of these chemicals leads to xerosis directly proportional to the amount of lipid removed. Treatment of the skin with petrolatum increases the rapidity with which these lipids are synthesized in the skin.
Petrolatum impacts all phases of skin remoisturization, the first step toward barrier repair and wound healing. Remoisturization of the skin occurs in four steps: initiation of barrier repair, alteration of surface cutaneous moisture partition coefficient, onset of dermal-epidermal moisture diffusion, and synthesis of intercellular lipids. It is generally thought that a stratum corneum containing between 20% and 35% water will exhibit the softness and pliability of normal stratum corneum. Petrolatum allows the water content to rise by decreasing evaporative losses, which creates the moist environment necessary for fibroblast migration leading to wound healing and eventual barrier restoration.
Petrolatum is a remarkably inert substance. It does not bind proteins or undergo chemical alteration in the skin. It is these qualities that account for the fact that petrolatum is not allergenic or a cutaneous irritant. Petrolatum is used as the negative control for patch testing by many dermatologists. It is also used as a carrier for many of the ingredients on the dermatologist’s standard patch test tray.
The comedogenicity of petrolatum is somewhat controversial, if standard lists of comedogenic substances are reviewed. It is important to recognize that comedone formation is based on the formation of a follicular plug, not on the oiliness or greasiness of the substance applied to the skin surface. While oily or greasy substances can occlude the skin surface and the eccrine sweat ducts, resulting in the immediate formation of miliaria, comedone formation is a process requiring prolonged skin contact.
Petrolatum is a hydrocarbon and can easily contain impurities, if not well manufactured. Poor quality petrolatum may indeed contain tar impurities and tar is a known comedogen, however, cosmetic grade petrolatum is devoid of tar impurities and does not cause comedone formation. Perhaps some of the confusion regarding the comedogenicity of petrolatum is due to the comedogenicity of the impurities.
Outside of water, petrolatum is one of the most biologically active substances applied to the skin surface. It fits the definition of a cosmeceutical, since it is a cosmetic with pharmaceutical significance. Petrolatum decreases the appearance of fine lines on the face and body due to dehydration. It functions to reduce itching and mild pain by creating a protective film over exposed lower epidermal and dermal nerve endings. It acts as an emollient by entering the space between the rough edges of desqauamating corneocytes, restoring a smooth skin surface. It can also function as an exfoliant by loosening desquamating corneocytes, which are physically removed as the petrolatum is rubbed into the skin. Petrolatum is also an important component of many other cosmeceutical formulations that contain additional actives.
Petrolatum is commonly used as a drug delivery vehicle in topical medications, such as topical corticosteroids. It can be used in concentrations up to 90% (by weight) in such preparations. It also increases the amount of time topical medications contact the skin surface due to its inherent substantivity. Petrolatum is also excellent at forming a film over the skin surface. Topical drug delivery is dependent on the uniformity of the film that contacts the stratum corneum. Any film will become discontinuous after application with time, but a petrolatum vehicle can be rubbed to reestablish the uniformity of the film and restore optimum topical drug delivery.
Many novel ingredients have been introduced into the skin care market, but only a few withstand the test of time. Petrolatum is one substance that has established itself as a valuable additive to skin care products both in the over-the-counter and the prescription realm. Petrolatum is a hypoallergenic, noncomedogenic additive that is technically a cosmeceutical, given its profound effect on the stratum corneum. It is chemically complex and has therefore never been duplicated synthetically. Petrolatum remains an important part of the dermatologic armamentarium.