Accompanying the record growth of anti-ageing cosmeceuticals are ingredients addressing the primary source of visible ageing — UV light or radiation. Guy Langer examines recent sun care strategies, regulations and consumer products and what future approaches to formulations can be expected
Three types of UV light or radiation occur in nature. UVC rays are virtually blocked by the stratospheric ozone layer. UVB rays are higher energy but lower penetrating to skin than UVA rays. UVB rays generate the redness, erythema or sunburn and consequential irritation. UVA rays are lower energy but deeper penetrating in the skin. UVA rays cause longer-term photo-ageing including hyperpigmentation, photoallergies, premature wrinkles, actinic keratoses and cancers.
For the purpose of this article, the words 'sun filter' refer to a sunscreen active, such as octyl methoxycinnamate (octinoxate). The word 'sunscreen' refers to a finished product. Sunscreens exhibit an SPF (sun protection factor) number and are regulated as OTC drugs by the US Food and Drug Administration.
Increasingly, sunscreens incorporate added ingredients for more claims and benefits.
Any product with a designated SPF and certain sun-protection claims must adhere to the FDA monograph for OTC drugs. The most recent monograph is from 1978 and designates 22 ingredients as sun filters or sunblocks. In 1999, the FDA proposed rule and label changes to the monograph that constitute the tentative final monograph (TFM). Until the TFM is finalised, the original monograph governs actives, claims and labelling.
Specifically, there are organic or chemical sunscreens listed in order of quantity, which largely absorb UV energy. These include octyl methoxycinnamate (octinoxate), benzophenone 3 (oxybenzone), octyl salicylate (octisalate), octocrylene, menthyl anthranilate (meradimate), and homo-salate. Other organic or chemical sunscreens include PABA; Padimate O (octyl dimethyl paba); cinnamates (cinoxate); and a water-soluble UVB sun filter, phenylbenzimidazole sulfonic acid. The usage of PABA and padimate O has decreased in the last 10 years due to irritation potential and poor market perception.
The only recently new organic or chemical sunscreen available for UVA protection is avobenzone (Parsol 1789), supplied by DSM. There are other new sun filters such as Mexoryl and Tinosorb that remain unapproved for American sun care. The FDA expects to complete a review of these compounds in the next few years. Meanwhile, Mexoryl is patented by L'Oreal and Tinosorb by Beiersdorf.
Two inorganic or physical sunscreens, titanium dioxide (TiO2) and zinc oxide, tend to reflect or scatter energy rather than absorb it. They are based on inorganic salts and have been growing in popularity over the last 10 years due to their broad-spectrum properties and generally safer irritation potential than many organic or chemical sunscreens. There are smaller-size titanium and zinc oxide particles and better emulsifiers and formulations to assist in the creation of aesthetically acceptable finished products. Titanium dioxide and zinc oxide are commonly supplied as dispersions for ease of handling and formulation.
It is important to bear in mind that a company cannot make any SPF claims either directly by designating it numerically (eg, SPF25) or indirectly by inference unless the above-designated sunscreens in the monograph are utilised up to specific maximum levels. In addition, the finished product must be in vivo tested after being manufactured in an FDA-approved facility.
Advances in formulations
The deleterious effects of sun exposure have prompted companies to develop formulas containing additional ingredients to help boost SPF (such as film formers), offset free radical damage, moisturize or hydrate the skin, control MMP (Matrix Methlloproteinoses), and even address DNA damage.
Sunscreen formulations have traditionally been water-in-oil systems inasmuch as nearly all sun filters are oil soluble. These types of creams or lotions were aesthetically acceptable since most products had SPF values of two to 15. In the last 10 years, the consumer market has seen products offered with SPF values of 15, 20, 30 and greater. Typically, these products utilised organic or chemical sunscreens. In fact, in today's sunscreen market in the US, the lowest suggested SPF is 15 and many products claim SPFs of 30, 45 and even above 50.
Newer sunscreen emulsion systems are based not on the HLB system using water-in-oil emulsions but water-in-silicone, liquid crystal gel systems and polymeric emulsions. These newer systems allow for delivery of physical sunscreens such as TiO2 and zinc oxide, which in combination can develop SPF values of 30 plus and provide both UVA and UVB coverage.
Ultrafine TiO2 and zinc oxide particles also have given formulators better aesthetics than previously. Whereas TiO2 and zinc oxide used to have a PPS of 50 or 60nm, now TiO2 and zinc oxide products have a primary particle size of 10-20nm. Thus, the aesthetic issues of whitening, streaking and bluing upon application have been reduced.
Formulators have used the following guidelines to estimate the final SPF of their product formulations: organic or chemical sunscreens generate one SPF value for every one per cent of active sun filter, whereas TiO2 provides two or three SPF values per every one per cent of TiO2. Since avobenzone and zinc oxide are really UVA filters, they tend to produce 0.5-1.5 per cent SPV value per every one per cent of active sun filter. These values depend on the formula.
The goal is to deliver the sunfilter evenly on the skin and ensure coverage along the peaks and valleys of the skin's surface including the user's fine lines, wrinkles, sweat glands and hair follicles. Recent formulation advances have allowed manufacturers to generate two times or more SPF values for every one per cent of active organic or chemical sunscreen and three-to-five times the SPF value for every 1 per cent of TiO2. The result is better protection with less actual sunscreen, which is less costly, gentler to the skin and more aesthetically acceptable — that is, less greasy and grainy.
Film formers in sunscreen formulas help boost SPF and resist wash-off or sweat. Historically, waxes such as carnauba wax were used to resist wash-off and make waterproof or water-resistant claims. More recently, the claim of waterproof or water-resistant sunscreens is based on using film formers like Ganex from ISP, which are based on PVP (polyvinyl pyrrolidone) derivatives and polymers such as polyolprepolymes from Bertek Pharmaceutical. Water-resistant claims can be made only if the film former has passed the waterproof test based on FDA protocol in which the subjects apply the sunscreen and immerse themselves in water multiple times over eight hours.
It is important also to differentiate among different types of film formers. The PVP derivatives such as Ganex from ISP or Unimers from Induchem generate a continuous film, which can be occlusive. Some of the newer polymeric film formers from Bertek (polyolprepolymer) or Lonza create 'reservoirs' to hold the sunscreen on the surface and resist wash-off, sweat and penetration. These materials allow for normal skin respiration and are non-occlusive. Controlling sun filter deposition can boost SPF and reduce irritation or allergic reactions to chemical sunfilters.
Sunscreen formulas have employed antioxidants for decades to reduce free-radical damage from UV exposure. This free-radical damage includes lipid peroxidation, the proliferation of superoxide, hydroxyl radicals and hydrogen peroxide. All human cells and even those of animals have a cell membrane composed of phospholipids. These lipids, which are similar to lecithin, are subject to oxidative damage throughout the life of a cell. Solar radiation hastens the oxidative process, which can cause apoptosis or cell death. Thus, controlling this oxidation can help reduce peeling and hyperpigmentation.
Vitamins C and E (ascorbic acid ester and tocopherol or tocopheryl acetate) are some of the popular antioxidants in use. In the body, vitamin E protects vitamin C and vitamin C 'recycles' vitamin E in what is called a redox reaction. Because vitamin C as ascorbic acid is unstable in formulations, formulators use esters or oil-soluble versions of vitamin C. Probably the most popular and stable type is ascorbyl tetraisopalmitate (BU-OSC, marketed by Barnet Products). DSM (formerly Roche) markets a stable form of vitamin C, as do other suppliers like Tri-K Industries. The principal suppliers of vitamin E are BASF, DSM, Henkel Esai and Tri-K Industries. Consumers also recognise these two antioxidant vitamins as desirable since they are among the most popular supplements as well. Thus, inclusion of these vitamins is a natural choice.
Many other antioxidant ingredients are used to improve overall sun care protection.
Tea derivatives from Camellia sinensis contain polyphenols reported to protect skin from free-radical damage. These polyphenols include catechins such as EGCG (epigallicathecin gallate). Green and white teas are the best sources of EGCG. While most teas are from Camellia sinensis, the colour difference and polyphenol content are largely the result of when the plant is harvested. White tea results from the harvesting of 'buds' when the plant is immature but is especially rich in polyphenols. An antioxidant test comparing vitamin E, alpha-lipoic acid, green tea and white tea showed white tea to be the superior antioxidant.
Alpha-lipoic acid (ALA) is a sulfur-containing material that has the ability to be soluble in both water and oil (lipids). That unique feature and the fact it is involved with the redox reaction of recycling vitamin E in the skin makes it another powerful antioxidant. ALA, however, does have a bright yellow colour and sulfur odour, which can confer undesirable properties to a formula.
Coenzyme Q10 (ubiquoinone) and its synthetic cousin idebedone are strong antioxidants but their use and claims are covered by numerous patents. Both are also yellowish-orange in colour and can be tricky to stabilise.
Auto Defense Complex (ADC Complex) from Barnet Products is a new antioxidant mixture with in vivo testing. ADC Complex is composed of pear, ferula, hibiscus and green tea extracts and was in vivo tested to scavenge free radicals and reduce apoptosis (cell death). ADC Complex was superior to vitamin E, polyphenols from grape and green tea in the test, and conferred protection equal to an SPF 15 alone.
L-ergothioneine is an amino acid marketed as Thiotaine, and has also been utilised in conjunction with other antioxidants. L-ergothioneine is found in the lens of the human eye to protect against UV damage as well as hemoglobin to protect oxygen transport in the blood. It occurs naturally in mushrooms and other plants, although the commercial version manufactured by AGI Dermatics is biomimetic.
GliSODin is an antioxidant that stimulates the body's production of its endogenous antioxidants, including superoxide dismutase (SOD), catalase and glutathione peroxidase. Two recent studies show that GliSODin appears to help protect against oxidative stress resulting from exposure to UV radiation, particularly for fair-skinned people. A follow-up study in France found volunteers supplementing with it did not present sunburn, flushing or skin rash after sun exposure.
Pycnogenol is a standardised extract of the bark of the French maritime pine, Pinus pinaster, with multiple biological effects, including antioxidant, anti-inflammatory and anticarcinogenic properties. One recent rodent study found that applying a topical lotion containing pycnogenol immediately after exposure to UV radiation reduced the inflammatory sunburn reaction and significantly delayed tumour appearance. This study was notable because pycnogenol demonstrated activity when applied to the skin after, and not before, UV exposure.
Catechins, types of polyphenols found in green and white tea, are also present in a host of botanicals, including licorice extracts as well as chocolate and vanilla extracts. We will discuss licorice later in reviewing anti-irritants/anti-inflammatories. A number of chocolate and vanilla extracts, rich in polyphenols, have been tested as antioxidants and reducers of apoptosis. Solabia offers Caophenol, a cocoa extract rich in polyphenols, which shows protection from UV exposure. In fact, a German study showed promising results for sun protection by patients consuming a cocoa-extract beverage rich in flavonoids.
Expanscience markets a product called Heliorea, which is a Tahitian vanilla extract rich in polyphenols and shown to reduce erythema and sunburn cells.
Grapeseed and grapeskin extracts have well-documented antioxidant benefits and have been added to sunscreen formulas for that reason.
Many sunscreen products contain anti-inflammatory or anti-irritant ingredients. This is because sun exposure causes redness and irritation and high-SPF products containing organic or chemical sun filters may sensitise the skin. Physical sun filters do not sensitize skin and are the preferred actives for baby's and kid's sunscreen products. Allantoin and bisabolol have been used for decades and continue to be popular.
Glycyrrhiza licorice extracts such as glycyrrhetinic acid, dipotassium glycyrrhizinate and stearyl glycyrrhetinate have been used in the past 10 years. Standardised licorice compounds are powerful anti-irritants, stronger than the ethical drug indomethacin. Licorice anti-inflammatories are widely used in international formulations because of their excellent performance and acceptance in the Asia Pacific market.
Centipeda cunninghami, the Australian plant, is a unique anti-inflammatory, marketed as Phytophenolin by Bio Botanica. It has several in vivo anti-irritant tests. Many anti-irritants have antierythema test data, which may boost SPF and reduce sunburn.
Triple A Complex is an algae and mugwort mixture marketed by Barnet Products and used by many direct sellers like Herbalife, NuSkin and Neways. Test data show one per cent Triple A Complex reduces erythema as much as an SPF 8 sunscreen product.
Solaleur is another new antierythema agent. From the Hawaiian company, Oils of Aloha, Solaleur is a proprietary mixture of Hawaiian kukui nut oil, macadamia nut oil and vitamins that tests show reduce erythema by 35-60 per cent when used in sunscreen formulas at only five per cent.
MMP Controls: Apart from burning and irritation, high-tech formulations are employing ingredients to address MMP proliferation. MMP are protein-degrading enzymes like collagenase, elastase and hyaluronidase that naturally occur and break down collagen, elastin, fibronectin and hyaluronic acid. This is a normal process that involves healing and repair of tissue. However, UV radiation causes an over-proliferation of MMPs, resulting in compromised skin integrity, slackness and moisture loss.
Atrium offers MDI Complex, a shark derivative, tested to reduce MMP damage. ACTIMP, a lupine peptide product, from Expanscience, also has some compelling MMP-inhibiting test data. Expanscience also has a product from wheat germ called BAR-TIMP, which boosts the body's natural opposers of MMPs — tissue inhibitors of metalloproteinases. TIMPs modulate MMPs in an in vivo test and represent a more sophisticated way of reducing protein damage from UV radiation.
As new functional ingredients are being incorporated into sunscreen products, formulations have become more varied and sophisticated. Emulsions remain the most popular form of delivering sun filters in creams and lotions. Sun-care products also are sold as gels, oils, ointments, pump sprays, sticks, mousses and aerosols.
Spray products, either from pump or aerosol, are convenient and less messy but are generally not used on the face. Mousses and foams have been developed for especially hairy areas.
Coppertone has an entire line of continuous-spray products with SPFs up to 50, which the company claims are unnecessary to rub in and can be dispensed from any angle. Banana Boat has a line called Ultramist with SPFs up to 50 as well, and Hawaiian Tropic offers several spray products with SPFs of 60 plus. Among the most innovative sunscreen products are aerosol sprays from Neutrogena that contain cryolidone, from UCIB, a reacted, odourless menthol that cools when applied — very cool indeed.
Children's sun care products tend to utilise physical sunscreens that are non-irritating and have different fragrances. The FDA recommends protecting kids and babies from UV exposure at all times, either with clothing and/or broad-spectrum sunscreens. Inasmuch as skin cancer is a function of the cumulative amount of UV radiation one receives over a lifetime, early protection is essential.
Up for debate
D deficiency: As dangerous as UV radiation is, some recent studies suggest avoiding sun exposure completely subjects people to the risk of vitamin D deficiency, which contributes to osteoporosis and even some types of cancer. Even the FDA suggests limited sun exposure to ensure sufficient vitamin D production. Five or ten minutes a few times a week during off-peak hours is usually sufficient.
Cancer: Another ongoing debate is whether sunscreens cause cancer by protecting against only UVB radiation, thus allowing more UVA into the skin. No scientific studies prove the connection, although despite an unprecedented use of sunscreens, skin-cancer cases continue to grow. One of the two true UVA sun filters, avobenzone, has been examined for its photostability. That is, after an hour or two of UV exposure, it can degrade. Some companies — Neutrogena, for instance — use a product called Helioplex to stabilise avobenzone to maintain its efficacy.
Nanotech: The buzz about nanotechnology also has raised some concerns about the safety of ultra-fine TiO2 and zinc oxide penetrating the skin and causing systemic problems. While the primary particle size of these products may be 10-50 nm, they tend to reagglomerate in the formulation and wind up being 150-250 nm. At those larger sizes, penetration is less of an issue but thus far no study has indicated a safety issue. More information on this will surely come.
New regulations: The FDA continues to study comments on the TFM whose changes include: maximum of 30+ SPF, water resistant or very water resistant, no 'all day' or 'photoaging protection' claims, and no use of the word 'sunblock,' to name a few. In addition, they are considering approval of a half-dozen sun filters used in Europe and Japan such as Mexoryl, which is owned by L'Oreal and offers complete UVA/UVB protection. Until the TFM is adopted, companies have continued to adhere to the current monograph.
Guy Langer is vice president of marketing for DD Chemco and an authority in cosmeceutical product development, ingredient technology, sourcing, formulation and marketing.
Respond: [email protected]