Sunscreens are supposed to prevent aging, sunburn, tanning, and skin cancer. Correct? The answer is “no,” however one might be tempted to say “yes” based on the marketing claims and information presented in the popular press. Perhaps a better way to formulate an answer to this seemingly simple question is to examine the history of sunscreen development. The original sunscreens were commissioned by the federal government to prevent heat stroke and debilitating sunburn in military personnel who worked long hours in the sun on the deck of aircraft carriers. Many of these carriers were stationed in the intense sun around the equator and recruits were falling sick with the reflected sun from the shiny ship deck. The recognition of this need stimulated research in the development of a product that could be topically applied to the skin to decrease sunburn, which was the birth of sunscreen.
The first sunscreen was red veterinary petrolatum. While it provided modest UVB photoprotection, it was not terribly effective and lacked in aesthetic appeal. The search for new sunscreen ingredients resulted in the development of PABA, a better UVB photoprotectant, but unfortunately PABA stained white clothing yellow, also causing problems. Since that time more UVB photoprotectants, such as octyl methoxycinnamate, have been developed that do not stain clothing and provide better UVB protection. More modern sunscreen formulations contain ingredients such as photostabilized avobenzone, oxybenzone, microfine zinc oxide, and micronized titanium dioxide that offer both UVB and UVA photoprotection with excellent aesthetics and no clothing staining.
With these tremendous developments, sunscreens should be highly effective. Is this correct? The answer again is “no.” Sunscreens were never intended to prevent sunburn or tanning. Sunscreens only prolong the amount of sun exposure than can be received until burning or tanning occurs. Further, sunscreens have never been proven to prevent skin cancer, although our clinical acumen tells us that people who wear sunscreen have fewer actinic keratoses and skin cancers, but the double blind placebo controlled trial has never been run and will never be run due to ethical issues. Sunscreens are no substitute for sun avoidance or clothing. They are the best that is available in situations where sun exposure cannot be avoided and clothing cannot be worn.
Perhaps the most controversial area of sunscreen use is in the prevention of premature aging. Do sunscreens prevent aging? The answer is “no one is sure.” Again, the studies have not been done and data is lacking. It makes sense to assume that less sun exposure will result in less skin aging, but no one knows if wearing sunscreen decreases sun exposure sufficiently to reduce skin aging. New evidence indicates that visible light and infrared radiation also cause skin aging and these wavelengths are not blocked by sunscreens. This might indicate that sunscreens are not superb in preventing aging, but they are the best option currently available. Most products that claim to be “anti-aging” use the inclusion of sunscreen actives as the basis for the claim.
This then leads us back to our initial question as to the safety of sunscreens. Are sunscreens safe? Perhaps the best answer is “it depends.” The safety of sunscreens has recently been called into question by several consumer groups purporting that sunscreens are proestrogenic and cause cancer. Much of the data to support these contentions comes from studies where rodents were fed massive amounts of sunscreen. Clearly, sunscreens are not intended for ingestion, but accidental ingestion does occur, especially in children. It is possible to isolate sunscreen actives from the urine of humans who use them, so we know that some systemic effects do occur. What are the ramifications of systemic sunscreen absorption? No one knows.
Sunscreens are the most effective product currently available for photoprotection of the face, but the safety issues cannot be ignored. What should we as dermatologists recommend to our patients? I would recommend the following:
Only wear sunscreen-containing products during the day when sun exposure may occur. Do not use sunscreen-containing moisturizers at night. Buy a separate product for nighttime application, cutting the sunscreen exposure in half.
Do not use sunscreens on children less than 6 months old where the ration of body surface to body mass is high. Keep these infants out of the sun.
Only apply sunscreen on areas of the skin that will be exposed to sun and not under clothing. Remember that clothing provides the best and safest photoprotection.
Avoid ingesting the sunscreen when possible. Use specialized sunscreen-containing lip balms that minimize oral ingestion on the lips and not regular sunscreens.
There is nothing in life that is thoroughly safe, including the use of sunscreens. Everything must be assessed in terms of a risk/benefit ratio. Sunscreens have a very low risk/benefit ratio, but research is needed to better understand the protection of skin from the sun. The sun gives life and the sun takes away from the beauty of the skin. Protection is vital and dermatology must lead the way in the development of better photoprotection methods.
Sunscreens are an important part of the dermatologist’s armamentarium for the prevention and treatment of aging. A thorough understanding of sunscreen formulation issues is a must for providing quality patient advice regarding sunscreen recommendations. Part one of this series dealt with issues regarding sunscreen type and the currently available UVB and UVA ingredients available to deliver sun protection. In this discussion, we shall examine the methods used to develop SPF ratings and the requirements for meeting water resistance. The discussion will continue with an examination of how sunscreens fail in the presence of water contact and how this translates into actual photoprotection achieved while perspiring or engaging in water sports. Lastly, the issue of active sunscreen ingredient interaction will also be examined.
Do sunscreens work? The answer is yes, provided that they are formulated and used properly. Some of the recent concern regarding the inability of sunscreen use to prevent skin cancer probably has to do with consumer misconceptions regarding photoprotection. First, sunscreens are primarily UVB protectants, as indicated by the SPF, and UVB protection alone will prevent sunburn, but not skin cancer. Second, SPF ratings are a laboratory determination not directly linked to actual use. This topic will be discussed in detail. Third, the water-resistant and film forming characteristics of the sunscreen formulation are probably the most important factors, more important than laboratory SPF, in determining the actual performance of the sunscreen. These qualities are difficult for the consumer to assess.
The SPF is currently the only comparative rating available for determining the superiority of one product over another in terms of possible sun protection. Patients are misled, however, when they purchase products on the basis of SPF alone. There is no substitute for a quality formulation from a reputable manufacturer.
Both chemical and biologic methods are used to determine the SPF, however, only the biologic evaluation will be discussed in this article. Most commonly, the lower back of untanned individuals is divided into small test sites and exposed to UVB light until a minimum amount of erythema develops, known as the MED. Lightproof barriers are placed around the test sites to prevent light contamination from one test site to another. Once the MED for the test subject has been determined, the subject is invited to return to the test site the next day for application of sunscreen. The sunscreen is placed on the test sites and allowed to dry. The skin is then exposed to UVB light at the expected SPF of the sunscreen product. The expected SPF is roughly determined by spectrophotometric absorption. The amount of UVB light required to obtain the same degree of erythema as the preceding day is determined and the SPF calculated.
This measurement is the optimum SPF the product can deliver under optimum conditions. The subjects have a measured amount of the product rubbed into the skin by a skilled technician. This eliminates the complicating factor of too little sunscreen applied in an erratic manner. Subjects are also evaluated indoors, eliminating the effects of wind, humidity, and perspiration due to high temperature. In my opinion, the biologic SPF determined under laboratory conditions in human test subjects should be halved to give an approximation of what can actually be expected under actual use conditions.
As mentioned previously, water-resistant qualities are very important in maintaining the SPF of the sunscreen under actual use conditions. Separate testing must be conducted to meet criteria required by the FDA to place this label on a sunscreen bottle. Water resistance is determined by applying the sunscreen with a predetermined SPF to human volunteers over a body surface area of 50 square centimeters. The product is allowed to dry for 20 minutes and reapplied with another 20 minutes allowed for drying. The subjects are then asked to swim in an indoor pool for 20 minutes. The skin is then dried and the subjects sit outside the pool and rest for 20 minutes. The subjects then reenter the pool for another 20 minutes. A total of 40 minutes of water contact is required to substantiate water-resistant claims.
The SPF of the product is determined after this routine of water contact and skin drying. If the SPF following water contact is the same as the SPF prior to water contact, the product is considered to be water resistant. This testing also maximizes the water-resistant characteristics of the sunscreen. Notice that two applications of the sunscreen are performed prior to water contact. Also notice that the sunscreen is allowed to dry for 20 minutes prior to water contact. Double application ensures good coverage while the drying period maximizes substantivity of the product for the skin. This is the advice that should be given to patients who expose themselves and their children to the sun at the beach. The patient should do everything possible to maximize the water resistant qualities of the sunscreen since the product will not perform up to standards in real life at the beach, since the effects of wind and sand have been eliminated in the indoor pool environment used to perform the testing.
There is a great deal of chemical science that goes into the development of a successful water-resistant sunscreen. The basic methods of imparting water resistance are listed in Table 1. All of the technologies for imparting water resistance are predicated on the fact that water soluble and oil soluble substances do not mix meaning that water can dissolve water soluble substances, but not oil soluble substances. Thus, if a sunscreen is predominantly oil, with minimal water, it will not solubulize in the presence of water or perspiration. However, oil dominant sunscreens are greasy and sticky. This has led to development of silicone liquid based sunscreens, since silicone is an oil that is not greasy or sticky with excellent water resistant properties.
Another method of creating water resistance is to alter or eliminate the emulsifier. Remember that the function of an emulsifier is to allow water and oil loving substances to mix into one continuous phase. The emulsifier in the sunscreen formulation can allow perspiration or swimming pool water to mix with the oily ingredients facilitating removal. Thus, acrylate crosspolymers and liquid crystal gels are being used where no emulsifier or hydrophobic emulsifiers can prevent solubulization of the sunscreen film by water.
The last methods used to confer water resistance are predicated on creating a film that is resistant to water removal. One technique involves the use of phospholipids, which are structurally similar to natural sebum, and create a thin oily film on the skin. The other technique involves the use of polymers that leave a thin water-resistant film on the skin surface.
How do sunscreens fail to exhibit water resistance with the aforementioned technology. All dermatologists have seen patients who have experienced severe, blistering, second-degree sunburns at the beach while wearing sunscreen. What went wrong? Was an inadequate amount of sunscreen applied? Was the sunscreen not applied at regular hourly intervals? Did the sunscreen wash off? Possibly. Part of the problem could have been inadequate periodic application, but it is also possible that the sunscreen was not water-resistant. The methods that sunscreens can be removed from the skin by water are listed in Table 2.
There are three primary mechanisms that account for the removal of sunscreens from the skin surface. One method is water actually dissolving the oily sunscreen film by interacting with the emulsifier in the formulation. This means that the emulsifier in water-resistant sunscreens must of low concentration or possibly eliminated. For this reason, many of the best water-resistant and water proof sunscreens are anhydrous, meaning they contain no water. Products that are anhydrous do not require an emulsifier. This point should be emphasized to patients when selecting water-resistant sunscreens. Even though the patient may prefer a lighter feel in sunscreens, money and application time are wasted if the product is immediately removed upon water contact.
The second manner in which water-resistant sunscreens can fail is with rubbing removal. This can be the case if the sunscreen does not stick well to the skin, a quality known as substantivity. The rubbing of water over the sunscreen film on the skin can also mechanically remove the product by lifting it off the skin surface. This quality of a sunscreen is tested in part by the evaluation of the SPF following two 20 minute swims. Dermatologists who are interested in personally testing the ability of a sunscreen to remain in place on the skin should apply the sunscreen to a glass slide and allow it to thoroughly dry. The glass slide should then be swirled in a glass of water. If the sunscreen film is even and continuous, it will remain on the slide and the water will remain clear. If a thin film is seen in the glass or the water becomes cloudy, the sunscreen has failed the test.
Lastly, the sunscreen film can physically degrade, a phenomenon most commonly seen with particulate sunscreens containing micronized titanium dioxide or microfine zinc oxide. In this case, the oily sunscreen film or polymer film adheres well to the skin, but the water-soluble titanium dioxide or zinc oxide does not remain contained within the film. Water washes away the water-soluble particulates, leaving behind a film lacking some of the ingredients required to achieve the labeled SPF. This problem can be overcome by using hydrophobic grades of titanium dioxide.
The last issue to be discussed regarding sunscreen efficacy has to do with the care that must be taken to prevent undesirable photochemical breakdown or interactions between the UV filters and packaging. Many of the unwanted interactions can be suspected by the patient if the normally white sunscreen discolors to a pale yellow or brown color. These discolored products will not provide optimal sun protection and should be discarded. Discoloration may be seen in sunscreens containing octyl methoxycinnamate, which can undergo a photochemical reaction to form an intensely yellow pigment when exposed to sunlight. This can be prevented by packaging the sunscreen in an opaque container. Adding other UV absorbers, such as benzophenone-3 or zinc oxide, can stabilize the octyl methoxycinnamate while acting as active sunscreens and increasing the product SPF.
Degradation of another sort can occur with particulate sunscreens, such as micronized titanium dioxide or microfine zinc oxide. In order to be an effective sunscreen, the particles must be dispersed evenly within the sunscreen lotion. If the particles coalesce, an even film of the active sunscreen is not achieved on the skin and the SPF of the product is that of the unprotected skin. It is important that physical sunscreens are used within their expiration period so that the suspension remains intact. The suspension should be a white color and discolored products should also be discarded. The fragrance of particulate sunscreens can also disappear with time in suboptimal formulations as it is absorbed by the titanium dioxide or zinc oxide. One of the newest developments that has improved the feel, water resistance, and SPF of physical sunscreens is the incorporation of film-forming polymers, such as acrylate copolymers or PVP. These newer formulations are appearing in the marketplace currently.
UV filters can also be absorbed by plastic packaging or the cap inserts. For example, polystyrene and low density polyethylene can absorb the UV filters. For this reason, high density polyethylene or high density polypropylene must be chosen for packaging.
It is evident from this discussion that tremendous science, art, chemistry, and testing must be combined to achieve a successful sunscreen product. The UV filters selected must be placed in a stable vehicle that not only creates an even water-resistant film on the skin to maintain the labeled SPF, but also is perceived by the patient as aesthetically pleasing. The best sunscreen formulations combine oil-soluble and water-soluble UV filters that are attracted to both the hydrophobic and hydrophilic areas of the skin to provide maximum coverage. The packaging is selected to maintain the integrity of the sunscreen. .
Compliance is key to sunscreen efficacy. Sunscreens do not work if they remain in the bottle. It is estimated by sunscreen manufacturers that the average United States adult uses less than one bottle of sunscreen per year. Clearly, this is indicative of poor compliance, since one bottle, if applied as directed on a daily basis, should last one month. Why is sunscreen compliance an issue? There are many reasons, but I shall explore some of the major issues in this article.
One of the most common reasons patients do not like sunscreens is because they can be sticky. Perhaps it may be helpful to obtain more insight into this issue. Most of the chemical sunscreen actives, are sticky oils, such as methyl anthranilate. Usually a sunscreen formulation will combine at least 2-3 different actives to get broader spectrum coverage and a higher SPF. The SPF is increased as the concentration of the active is increased. Thus, higher SPF products are usually stickier. Sunscreens with an SPF of 30 or higher are usually stickier than sunscreens with an SPF of 15 or lower. Yet, an SPF of 15 blocks about 93% of the UVB radiation while an SPF of 30 blocks out 97% of the UV radiation. This is only a 4% difference in UVB photoprotection that may make the difference between an aesthetically pleasing sunscreen and one that is undesirable. For this reason, dermatologists should reconsider advising patients to use the highest SPF product possible. Lower SPF products generally have better aesthetics and may yield better compliance. My recommendation is that patients should use an SPF 15, which provides excellent photoprotection and optimal aesthetics.
Another common complaint regarding sunscreen use is that patients feel hot and sweaty while they are wearing sunscreens. While some of this may be due to the fact that sunscreens are worn in the hot sun, chemical sunscreens, such as octylmethoxycinnamate, benzophenone, methyl anthranilate, and homosalate, actually function by transforming UVB radiation to heat energy. This generation of heat by the sunscreen contributes to the feeling of skin warmth. This should not be a deterrent to wearing sunscreen, however, as the physical sunscreen agents, such as zinc oxide or titanium dioxide, do not produce heat. Selecting the proper sunscreen can help minimize this problem which may lead to decreased compliance.
Many patients have the perception that sunscreens cause acne. Usually the acne is in the form of inflammatory papules, not open or closed comedones, and presents within 48 hours after initial application. This is not true acne because sufficient time has not passed since the sunscreen application for follicular rupture to occur. The acne seen with sunscreens is more of an acneiform eruption, which I personally feel is indicative of irritant contact dermatitis. Some of the more extended wear water resistant sunscreens are more occlusive by nature and may cause difficulty at the follicular ostia. The solution to this problem is sorting through a variety of sunscreen formulations by trial and error. Major problems can be avoided by applying the sunscreen for five consecutive nights to a small area of skin in front of the ear. The skin should be observed for the presence of inflammatory papules and pustules. Another helpful tip is the avoidance of long wearing sunscreen products. For daily use, long wearing products are not necessary and a sunscreen containing moisturizer may be a good alternative. If a beach wear product is desired, the vehicle of gel sunscreens, which may contain a polymer, should be avoided. Instead, a light-weight cream formulation should be selected and then applied frequently to obtain maximal protection.
It is true that some sunscreens sting when applied and this is more common in gel sunscreen formulations with a high concentration of a volatile vehicle, such as alcohol. Creamy sunscreens are a possible solution to this problem, as well. Sunscreens may also sting when they enter the eye. One option is to use one of the waxy stick sunscreens in the eye area that will not melt or run when combined with sweat. These sunscreens can be stroked above the eyebrows and on the upper and lower eyelid. One of the methods for improving compliance is to pick the proper sunscreen for the proper skin site. No one sunscreen formulation will work in all body areas.
There are some who are skeptical of sunscreen efficacy from the start. This concern may be well founded, since sunscreens can fail. How does this occur? It is important to remember that sunscreens do not work unless present on the skin surface. Thus, failure to coat the entire exposed skin surface with sunscreen and sunscreen removal from rubbing or sweating are two of the most common causes of sunscreen failure. Sunscreens may also fail if the film applied to the skin is too thin. A thin film, created by failure to apply the proper amount of sunscreen, yields skin areas leaving the skin unprotected. Formulation issues are also important. Some sunscreens have better skin substantivity. Substantivity is a term used by the cosmetic chemist to explain the ability of the sunscreen to remain in place on the skin. Not all bottles of sunscreen with an identical SPF are equivalent. There is no substitute for the formulation knowledge of an experienced sunscreen manufacturer. By law, all products labeled with an SPF of 15, will provide consistent sun protection under optimal conditions. These optimal conditions include minimal perspiration, no water contact, low humidity, minimal activity, no wind, thick film application, etc. In reality, sunscreens are not worn under these conditions. The sunscreen in the bottle may be an SPF 15, but its performance on the skin may differ depending on formulation. I encourage my patients to avoid off brand sunscreens in favor of well established branded products.
Many simply do not like the way sunscreen looks on the skin. Some women complain that their facial foundation does not perform well when applied over sunscreen and the sunscreen makes their face look shiny and greasy. Again, careful sunscreen selection is important, however, many women can get excellent sun protection by using a sunscreen containing facial foundation. While most sunscreen containing facial foundations do not have an SPF higher than 8 for aesthetic reasons, an SPF 8 facial foundation blocks 88% of the received UVB radiation. This is excellent protection for casual sun exposure. Applying facial powder over the sunscreen can minimize the facial shine seen with some sunscreens. This decreases facial shine, increases the SPF of the sunscreen, and improves the ability of the sunscreen to remain on the skin.
Compliance is more important with sunscreen than any other topical over-the-counter drug, except for possibly toothpaste. I am reminded of the young child who asked which teeth he had to brush and the dentist replied, “only the ones you want to keep.” Patients frequently ask me where they should apply sunscreen. I think the proper reply should be “only the skin you want to be beautiful for the rest of your life.”
Many new developments have occurred in the sunscreen market to increase both efficacy and cosmetic acceptability. Higher SPF formulations are more popular as new sunscreen combinations arise that provide better UVB protection. New methods of increasing the longevity of UVA photoprotectants provide better broad-spectrum protection. Dry touch sunscreens have even been developed that dry quickly in place on the skin surface preventing rub-off and a gooey heavy feel. All of these advances make sunscreens able to provide superior photoprotection. This article examines some of the major active ingredients in sunscreens. These actives have all been in the marketplace for quite some time, since the FDA following the introduction of avobenzone has approved no new ingredients, however new uses for the time-tested ingredients are providing advanced sunscreen formulations.
Sunscreen actives can be classified into two major categories, chemical and physical. Chemical sunscreens undergo a chemical transformation, known as resonance delocalization, to absorb UV radiation and transform it to heat. This reaction occurs within the phenol ring, which contains an electron releasing group in the ortho and/or para position, and is irreversible rendering the sunscreen inactive once it has absorbed the UV radiation. Physical sunscreens, in contrast, are usually ground particulates that reflect or scatter UV radiation, absorbing relatively little of the energy. For this reason they have longer activity on the skin surface.
Sunscreen ingredients can be divided into the following three groups:
UVA absorbers: 320-360nm (benzophenones, anthranilates, avobenzone)
UVB absorbers: 290-320nm (PABA derivatives, salicylates, cinnamates)
UVB/UVA blocks: reflect or scatter UVA and UVB (titanium dioxide, zinc oxide)
Each of these sunscreen actives is discussed separately to highlight their advantages and disadvantages in formulation. Most modern sunscreen formulations are a blend of 2-3 actives carefully selected to compliment on another and enhance product performance. This discussion is designed to help the dermatologist under the compatibilities of various sunscreen ingredients.
There are 3 sunscreens in the benzophenone family: oxybenzone, dioxybenzone, and sulisobenzone. Oxybenzone is used in the US and provides weak UVA photoprotection below 320 nm. There have been some reports of allergic contact dermatitis to benzophenone, but they are rare. Benzophenone is commonly used as a secondary sunscreen to increase the broad spectrum protection of the formulation. It is an oil soluble ingredient that can add to the sticky feel of a sunscreen, if used in too high a concentration. Benzophenone has found a new importance in the sunscreen industry for its ability to stabilize avobenzone, an important UVA photoprotectant discussed next.
Avobenzone, also known as Parsol 1789, was an important step forward in UVA photoprotection. Unfortunately, it is highly photounstable with 36% of the avobenzone destroyed shortly after sun exposure. It is estimated that all of the avobenzone is gone from a sunscreen after 5 hours or 50 Joules of exposure necessitating frequent reapplication. Avobenzone is also chemically incompatible with other commonly used physical sunscreens, such as zinc oxide and titanium dioxide. However, avobenzone has assumed new importance as a proprietary sunscreen complex, known as Helioplex (Neutrogena), has been introduced that combines avobenzone with oxybenzone and Hallbrite TQ to create a photostable avobenzone with longlasting UVA photoprotectant qualities. Hallbrite TQ is chemically known as 2-6-diethylhexylnaphthalate. Thus, Helioplex will provide for the United States what Mexoryl has provided for Europe and South America.
Menthyl anthranilate is the only sunscreen of this family approved in the US, where it is also known as meradimate. Its peak absorption is at 336 nm, but it is a clear thick sticky oil that can only be used in low concentrations in formulations for aesthetic reasons. It has a high safety profile and low allergenicity. It is very stable in formulation without the photodegradation issues discussed with avobenzone. It is commonly used as a secondary UVA photoprotectant.
For all practical purposes, the PABA derivatives are rarely used in modern sunscreen formulations. A recent review of marketplace showed that less 2% of sunscreens use PABA derivatives because of allergenicity concerns. Octyl dimethyl PABA, also known as Padimate O is the most commonly used with a maximal absorption at 296 nm. It has average photostability with about 15.5% lost to photoexposure.
The salicylates are an important class of UVB photoprotectants. This class includes: octyl salicylate (octisalate), homomenthyl salicylate (homosalate), and trolamine salicylate. It is the internal hydrogen bonding of the salicylates that provides for maximal UVB absorption at 300-310 nm. Approximately 56% of the sunscreens in the current marketplace use the salicylates as a secondary sunscreen active since they have an excellent safety record with minimal allergenicity.
The cinnamates are the most popular sunscreen category currently used in true sunscreens, sunscreen-containing moisturizers, and facial foundations. 86% of products with an SPF rating contain octyl methoxycinnamate, also known as Octinoxate, which has maximal absorption at 305 nm. Octyl methoxycinnamate has excellent photostability with only 4.5% degradation after UVB exposure.
The physical UVA/UVB absorbers are titanium dioxide and zinc oxide. Titanium dioxide is usually micronized to contain particles of many sizes to provide optimal UV scattering abilities. Unfortunately, it leaves a white film on the skin and is used mainly for beach wear products. Zinc oxide is usually available in a microfine form meaning it contains small particles of one size making it appropriate for day wear. A newly introduced colorless zinc oxide with extremely small particles is finding its way into many cosmetics and moisturizers.
There are many sunscreens available in Europe and Asia that are not approved in the US. The most publicized sunscreen active not approved in the US is Mexoryl. Mexoryl was originally developed to stabilize avobenzone, much like Helioplex discussed earlier. It is available in two forms: Mexoryl SX and Mexoryl XL. Mexoryl SX is a water-soluble form that is suitable for daywear sunscreen formulations. This would include sunscreen-containing moisturizers and facial foundations. Mexoryl XL is an oil soluble form that is suitable for water resistant sunscreen formulations, including those worn on the beach and during vigorous physical exercise. It is unknown when and if Mexoryl will be approved for sale in the US.
Sunscreens are typically made from combinations of the ingredients previously discussed. Usually, actives with different peaks of absorbency are combined to yield a sunscreen with the broadest protection possible. Oily ingredients are usually used in low concentration to prevent a sticky feel, but may be required to achieve the desired SPF. Sunscreen formulation is definitely an art, yet the question remains as to why sunscreens do not provide optimal protection. Careful formulation is only part of the success of a sunscreen. The ability of the sunscreen to be applied in an even thin film that will not separate or migrate is important. Sunscreens combine with sebum, sweat, topical medications, and cosmetics, which can interrupt or destroy the film. Furthermore, most sunscreens are tested in a laboratory under ideal wearing conditions. For practical purposes, it can be assumed that most sunscreens perform at half of their rated SPF.
Sunscreens remain an important part of dermatology with new developments creating longer lasting more aesthetic photoprotection. Current sunscreen research is aimed at creating better polymers to increase the length of time the sunscreen film remains in place on the skin, despite the presence of sebum and perspiration. Polymers also can suspend particulates, such as zinc oxide and titanium dioxide, allowing the film to appear invisible on the skin. It is hoped that the incorporation of new approved actives into the sunscreen monograph will further broaden skin photoprotection.