Skin deep beauty signifies a dream of having radiant skin with a uniform and clear complexion. But this beauty requires commitment; the consumer must have an intelligent skin care program based on cosmetic products. Moreover, the program must adapt to the physical changes that occur during the aging phenomenon.
Skin is a complex entity consisting of cells and tissues that form the outer surface of the body. As the first line of defense, it can suffer from a number of environmental insults, including temperature, humidity and solar energy. Changes in the skin are perceived as aging. This phenomenon is not simply a result of chronological aging but a reflection of the consequences of excessive ultraviolet (UV) exposure from the sun’s rays. It is a common perception that sun damage occurs only while sunbathing. However, this is only a part of the story. Sun damage occurs both indoors and out and at any time of the day, regardless if it is sunny or cloudy. During springtime even casual exposure can cause UV damage. Even on a cloudy day, 40-50% of the sun’s rays reach the earth. It may take 15-20 minutes for some to get burned; for others it takes 1-2 hours to initiate tanning.
The damage associated with wrinkling and skin cancer begins the moment our skin is exposed to sunshine. It is the repeated sun exposure, several minutes, 365 days a year, even while sitting next to a sunny glass window or outside in the shade, that adds up to great deal of damage both aesthetically and physically. Regrettably, windows do not protect us from the harmful effects of UV radiation. UVB rays (the ones that cause sunburn) do not filter through a window, but UVA rays pass through windows and cause damage that can lead to wrinkles and skin cancer. Therefore, daily UVA and UVB protection of the highly exposed areas such as face, neck and elbows is of paramount importance.
AGEs and Aging
Photoaging is a technical term for the premature aging of the skin, characterized by wrinkles on the surface, alteration of the pigmentation and loss of skin tone. At one time, researchers did not know how UV damages the skin’s extra-cellular matrix. But recent studies have revealed various biochemical processes in the skin, whose end products were found engaged in photoaging. One of these is Advanced Glycosylation End products (AGEs).1 The glycation or chemical attachment of glucose and ascorbic acid to the long-lived proteins, such as collagen and elastin, are responsible for the spontaneous formation of advanced glycosylation end products (AGEs), which are highly reactive in cross-linking protein. Protein cross-linking is important, since it is an irreversible process that is responsible for the permanent, deep wrinkling in the dermis. AGEs are, in a large part, responsible for the photoaging of the skin. The early stage of these spontaneous reactions, which are initiated by a condensation reaction between either reducing sugars, such as glucose, or oxidative products of ascorbic acid (L-threose) and the free amino groups of proteins (collagen and elastin), cause the birth of singlet oxygen radicals. These UVA photo-generated singlet oxygen radicals cause skin damage by disrupting the natural balance in skin by stimulating skin cells to synthesize metalloproteinases.
Metalloproteinases are enzymes that degrade collagen and elastin without synthesizing anti-metalloproteinases that hold skin protein degradation in check, which is a normal biological response. The unbalanced synthesis of metalloproteinases and anti-metalloproteinases caused by singlet oxygen radicals, leads to the breakdown of the extra-cellular matrix of skin. Because of the imperfect wound repair of the damaged collagenous matrix and the accumulation of elastotic material, known as solar elastosis or solar scar, the skin eventually sags and wrinkles after chronic UV exposure.
AGEs exposed to UVA radiation also cause photolytic oxidation; that is, the chemical decomposition by irradiation, of extra-cellular matrix proteins, which is mediated by the generation of reactive oxygen species. The mechanism first involves UV light, which enhances the generation of superoxide anions via UVA-AGEs induced electron transfer. This is accomplished through the cellular electron-transport chain in which UVA-AGEs energy enhances the passing of electrons onto ground state oxygen. This increases the generation of superoxide anions during the biosynthesis of adenosine triphosphate (ATP), the body’s molecular energy source. Next, superoxide anions are dismutated to hydrogen peroxide and oxygen by an enzyme called superoxide dismutase. Finally, hydrogen peroxide is converted to hydroxyl radicals in reactions catalyzed by iron and copper. Hydroxyl radicals cause tissue damage to the extracellular matrix of the skin by degrading collagen and elastin, which leads to imperfect wound healing and solar scars that photoage skin.
Several studies have shown that UV radiation increases the formation of AGEs on collagen, elastin and other skin proteins. This situation can accelerate the aging of skin by creating a vicious cycle, in which UV radiation accelerates the accumulation of AGEs in the skin. This in turn increases the potential for greater UVA-AGEs photosensitizing activity. Increased singlet oxygen and superoxide anion generation damages protein and ages skin even more.2
Protection for All Seasons
Scientists have pointed out that spring, fall and winter require different kinds of protection. The solar zenith angle becomes more oblique as winter approaches and ultraviolet photons are more efficiently absorbed by the stratospheric ozone layer and become ineffective. As a result, the skin is affected by the time of the day, season of the year and latitude. Compared to winter or spring, cutaneous damage is more frequent at the end of the summer due to excessive sun exposure. At the same time, there is more UVA exposure and less UVB due to the lack of atmosphere at higher elevation.
It takes more than an ordinary lotion or cream to emulate a radiant look. Knowledge about biological implications is required for any product applied to skin. Similarly, for the formulator, it is essential to know some biological and morphologic aspects to do a better job on the bench. The skin is the largest organ of the human body. It is a complex structure with multiple functional attributes. The most obvious is that it acts as a protective covering.
Using a variety of methods, the skin protects itself against penetration by alien substances. The sebum present on the surface of the skin is the first line of defense. This oily slick comes from the end point epidermal keratinocytes surrounded with lipids. These lipids consist of cholesterol, free fatty acids and ceramides. No phospholipids are present in sebum. Similarly, melanin provides an effective umbrella for the living cells in the upper skin, counteracting the highly destructive UVB rays. Melanin is a brown protective pigment produced by special cells called melanocytes present in the epidermis. The cross-section of the skin shows three distinct layers—the epidermis or horny layers, the dermis and sub-epidermis. The epidermis accounts for 2.5% of the total skin. The epidermis consists of two or three layers of living cells (keratinocytes) and a layer of dead cells–stratum corneum. The epidermis is protective in nature and very important from the cosmetic point of view. The dermis is essentially made up of elastic fibers out of collagen and proteoaminoglycans. These fibers lose their elasticity as skin ages. The dermis also consists of fibroblasts, macrophages and mast cells. Fibroblasts take part in the synthesis and remodeling of connective tissue proteins. The macrophages affect the immune system. Mast cells are present in layers of dermis and are concentrated around blood vessels. The dermis also has a scattering of sweat, sebaceous and lymph glands, blood vessels, nerves and hair follicles.
The dermis is important as it is pervaded with a mass of venules, arterioles and capillaries. The red blood vessels regulate body temperature. The actives or permeants, which are transported through stratum corneum, are ultimately removed by this dermal vasculature. The sub-epidermis is the inner most layer of skin and it provides a cushion between the external layers and the internal structure such as bone and muscle. The sub-epidermis is a water reservoir that stores fat cells.
Skin and Radiation
The skin is susceptible to incidental solar radiation and shows a structural heterogeneity that allows the absorption of some wavelengths and the transmission of others. Essentially, human skin is a three dimensional structure of three distinct compartments: stratum corneum, epidermis and dermis. The stratum corneum and epidermis are separated by a basement membrane. The epidermis and dermis contain several chromophores capable of interacting with incident solar energy. These interactions include reflection, refraction, absorption and transmission.
The UV spectrum is aribitrarily divided into three segments: C, B and A. This includes the wavelength between 10 and 400nm. UVC consists of wavelengths between 10 and 290nm and does not reach the earth because of its absorption by the stratospheric ozone. UVB consists of wavelengths between 290 and 320nm. This particular portion produces redness or erythema in human skin and is known as the sunburn spectrum. UVA represents wavelengths 320 and 400nm. The stratum corneum is a major hindrance to the transmission of UVB and less than 10% of incident wavelengths in this region penetrate the basement membrane. Approximately 3% of radiation below 300nm, 20% of radiation below 360nm and 33% of short visible radiation reaches the basal cell layer in non-tanned human skin. Proteins and nucleic acids in the skin cells absorb intensely in the short UVB.
In contrast, UVA penetrates the epidermis efficiently to reach the dermis, where it likely produces changes in structural and matrix proteins, particularly individuals with fair complexions. One of the consequences of UVB absorption by DNA has been the production of pyrimidine, particularly thymine dimmers. These structural changes can be repaired by mechanisms that result in their recognition, excision, and the re-establishment of normal base sequences. The efficient repair of these structural aberrations, is particularly crucial, since individuals with defective DNA repair are at high risk for the development of skin cancer. It has been observed that patients with xeroderma pigmentosum show variably decreased repair of UV-induced pyrimidine dimmers and may show xerotic appearance of photoaging. Their basal cell and squamous cell are also carcinomas and exhibit melanoma in the first two decades of life.
Photosensitivity and Chromophores
Sunscreen protects the skin from sunburn and photo damage by blocking the ultraviolet radiation before it is absorbed by the biological chromophores. Chromophores are photon-absorbing chemicals normally present in the skin. These are endogenous or exogenous chemical components that can absorb physical energy. Endogenous chromophores of skin are two types:
• chemicals that are normally present, including nucleic acids, proteins, lipids and cholesterol derivatives such as the precursor of vitamin D and
• chemicals, such as porphyrins, which synthesize elsewhere in the body, circulate in the bloodstream and diffuse into the skin. Photosensitivity occurs when a chromophore absorbs incident energy, becomes excited and transfers the absorbed energy to various structures or to oxygen. The absorbed energy subsequently dissipates by processes, which includes heat, fluorescence, and phosphorescence. For this phenomenon to occur it is necessary that at some point the absorption spectra and action spectra overlap each other.
Vitamin A (Retinoids)
UV radiation causes wrinkling of the skin and vitamin A has been the most common remedy. Vitamin A and its derivatives have been the most successful cosmetic active compounds to improve wrinkles. Vitamin A has a long history as a growth-promoting substance found in fish oils and butter fat. Vitamin A deficiency in man causes the skin appearance to be extremely dry and hyperkeratotic.3 These, as well as other studies, have been a great incentive to use vitamin A as a skin beneficial compound. However, if not properly formulated, vitamin A degrades easily. Its stability in an emulsion has to be monitored on a regular basis at various temperatures.
The immediate effects of sun exposure are sunburn and vitamin D synthesis. Sunburn is a common affliction of human skin and is caused by exposure to UVB and UVA regions. Photons in the shorter UVB are at least a thousand-fold more efficient than photons in part of the longer UVB and the UVA in evoking the response. The mechanism of skin injury has been closely co-related to the phenomenon that the action spectrum for UVB erythema has been found to be close to the absorption spectrum for DNA after adjusting for the absorbance of incident energy by the stratum corneum. Histamine and prostaglandin levels, present at the site are the two measurable variables after the afflictions caused by the UVA and B radiation. UVA erythematic results in less epidermal sunburn than UVB; however, it leads to erythemal damage, alters human skin and reduces the immune-response reaction. There may be also an age-related decline in the amount of inflammatory mediators detectable in human skin as well. The clinical features of photodamaged, sun-exposed skin consist of wrinkles, blotchiness, telangiectasia and a roughened, irregular, “weather-beaten” appearance. The researchers still do not agree, whether these changes, which we refer to as photoaging or dermatoheliosis, represent accelerated chronological aging or a separate and distinct process. Neverthe-less, the epidermis thickens and morphologic heterogeneity within the basal cell layer is observed with chronically sun-exposed skin. The dermis is the major site for sun-associated chronic damage, manifested as a massive increase in thickened irregular masses of tangled elastic fibers containing uncharacterized electron-dense material. Collagen fibers are also abnormally clumped in the deeper dermis. Fibroblasts are increased in number and show morphologic signs suggesting enhanced metabolic activity. Degraded mast cells may be seen in the dermis as well.
The two natural factors that protect the skin against UV damage are skin pigmentation and thickness of the stratum corneum. It has been observed that subjects who live in the southwest U.S. (commonly referred to as the “sunbelt”) have increased melanin contents and a thickened stratum corneum compared to those living in moderately sunny areas.
Product Development Guidelines
Sunscreens, vitamins A, E, K1 and C, low molecular weight amino-peptides, proteoaminoglycans, AHAs, natural herb extracts and emollients/moisturizers are a few ingredients incorporated into a cosmetic vehicle to slow down skin aging. Properly formulated sunscreen products can block UV radiation all the way to 400nm.
Inorganic sunscreens, titanium dioxide and zinc oxide, reflect, absorb and scatter the entire spectrum of UV rays. In contrast, organic chemical sunscreens such as octylmethoxy cinnamate, avobenzone and benzophenones, remain primarily in the stratum corneum, with the mechanisms of action involving the absorption of photons. Depending on their intended application, as traditional sunscreen or to assist in tanning the skin without any discomforts, its role in skin care products is well accepted. Anti-aging (wrinkle reducer) and safeguarding the skin from free radical attack have been two major known worthy attributes. It is good to have specific SPF numbers declared on the label but may be not necessary. Sunscreens should either scatter the incident light or they should absorb the erythemal portion of the sun’s radiant energy. Organic sunscreens absorb a specific range of UV radiation.
Every ingredient plays an important role in the development of a cosmetic that contains sunscreen. The emulsion base must be uniform, transparent and non-greasy, have an elegant silky feel and, above all, absorb or disappear quickly on the skin surface. This film should be of particular thickness, neither too thick nor thin, to create a uniform barrier against the UV rays.
Emulsions are constructed with many variables such as high water contents, emulsifiers, gum or polymeric thickeners, emollient esters (polar and non-polar), waxes, preservatives and perfume. How many variables of diverse nature are in cohesion to create an emulsion without causing instability to sunscreens or any other cosmetic active present? Today, we have emollient esters available that can boost the SPF numbers, thereby, making a cost-effective product. As most of the organic sunscreens are lipophilic, oil-soluble or -miscible therefore, has to be the most appropriate choice to develop an emulsion. It will also ease the manufacturing processes.
The polarity of an ester is another criteria that determines the correct UV curve and helps in providing uniform spread of the sunscreen on the skin. Similarly, for an ester, the end feel has to be drier and pleasant. Notable examples of SPF booster include diethylhexyl 2,6, naphthalate (HallBrite TQ) or butyloctyl salicylate (HallBrite BHB),4 neopentyl glycol dioctanoate/ diisostearate (Minno 21)5 and neopentyl glycol diisostearate/dioctanoate (Minno 41).6
To create a good emulsion, be sure to select a proper emulsifying system that matches the HLB requirements of the oil phase. We suggest Stepan-Mild RMI (sodium stearyl phthalamate),7 and Pemulen TR-1,8 5:1 ratio or Stepan-Mild RMI and Kessco GMS Pure in the ratio of 2:1.9 Sodium stearyl phthalamate has been described as an anionic emulsion stabilizer that functions through the formation of multiple-phase, oil-in-water emulsions with lamellar gel network structures. The emulsifying function can be strengthened with the addition of Pemulin TR-1 (a polymeric emulsifier). Fatty alcohols should be added to stabilize the emulsion.
Rheology is extremely important for the spreading mechanism and continuous availability of sunscreen actives on the site. It is imperative for the formulator to pick an appropriate emulsifying system that will not interact with the sunscreens or other cosmetic actives. Veegum, carbopol, xanthan gum and cellulose derivatives are excellent thickeners.
The inclusion of an efficient film former, pea extract or PVP/Hexdecene Copolymer10 can make the product water-resistant or waterproof or it can extend the product’s wear time.
Here’s an example of a typical beauty enhancing emulsion formula with an elegant feel.
q.s. to 100
|Aloe vera lyophilized powder||
|Sepigel 305 (Seppic)||
|Uvinul MS 40 (BASF)||
|Mag. Ascorbyl Phosp.||
|D. Panthenol 50%||
|Vitamin E acetate||
|Vitamin A palmitate||
|Butyloctyl salicylate (C.P. Hall)||
|Protoderm HA (Protameen)||
|Parsol 1789 (Roche)||
|Hysol 1% (Pentapharm)||
|Biopeptide E/L (Sederma)||
|Green tea extract||
The products are manufactured through cold processing and the pH is adjusted to pH4 4.5.
What’s Expected of a Product
The latest technological advances have enabled cosmetic chemists to create very effective and very stable products. Ideally, beauty products should have:
• An efficient sun blocking action with an improved photostability of organic sunscreens;
• A minimum two years of stability data;
• An elegant, silky feel, intended for daily use;
• Fast spreading ability, creating a uniform film;
• Resistance to perspiration wash away;
• Minimal or no irritation or sensitization;
• A pleasant fragrance and
• A moderate price.
Skin shows the signs of fatigue at certain times of the biological clock due to the environmental insults and normal wear and tear of the body in general. Skin ages like the other organs of the body and as a result it sags, wrinkles and shows blotchiness. Regrettably, there has been no single resolution to keep the clock running at the same pace as when we were younger. However, we have ways and means to slow down the aging clock by improving the skin’s appearance through cosmeceuticals and thereby, improving the quality of life. Recent advances in biochemistry and molecular biology have provided the details of abnormalities that occur at epidermal and subepidermal levels associated with skin aging.
We can apply two strategies of shielding and energizing the skin at once from environmental- and solar- related damages. One way is with sunscreens and the other way is by supplying deficient innate compounds such as amino acid peptides, vitamins A, E, K1 and C, proteoaminoglycans and other antioxidants through a cosmetic product.
Simultaneously, we can minimize, if not reverse, some skin damages by educating the consumers to follow a definite skin regimen program right from their teenage years. For skin protection SPF 4-15 has been considered to be the most appropriate. The latest findings and the usefulness of UVA sunscreen (Parsol 1789) present in all kinds of makeup forms, needs to be emphasized again to the color cosmetic chemist for future development work.
1. http: //www.arisc.com/reflect-page.html
3. Wolbach S.B and Howe, P.R., Tissue changes following deprivation of fat-soluble A, J. Exp. Med., 42, 753, 1925.
4. The C.P. Hall Co., 5851 West 73rd St., Bradford Park, IL 60499-0910.
5. Bernel Chemical Co. Inc., 174 Grand Ave., Englewood, NJ 07631.
7. Stepan Co., 100 West Hunter Ave., Maywood, NJ 07607.
8. The BFGoodrich Co., 9911 Brecksville Road, Brecksville, OH 44141-324.
9. Stepan Co. Inc.
10. International Specialty Products, 1361 Alps Road, Wayne, NJ 07470.