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Indian Journal of Dermatology, Venereology, and Leprology, Vol. 77, No. 2, March-April, 2011, pp. 238-243 Residents Page Sunscreens Sowmya Kaimal, Anil Abraham Department of Dermatology, St. John's Medical College Hospital, Bangalore - 560 034, India Correspondence Address: Anil Abraham, Department of Dermatology, St. John's Medical College Hospital, Bangalore - 560 034, India, docanilabe@yahoo.co.in Code Number: dv11069 PMID: 21393968 DOI: 10.4103/0378-6323.77480 Introduction Sunscreens are a constantly evolving component of the dermatologist′s therapeutic armamentarium. This article attempts to compile some of the important aspects of sunscreens, including their classification, various indices related to photoprotection, and some of the debatable issues related to sunscreens in general. The focus is on material which is current, while at the same time being relevant for the postgraduate. Indications for the use of Sunscreens The primary use of sunscreens is to protect the skin from the short-term and long-term effects of ultraviolet radiation. In today′s scenario of procedure-centered dermatology, sunscreens have become an indispensable part of every patient′s post-procedure skin care routine. The characteristics of an ideal sunscreen are listed in [Table - 1]. The common indications for the use of sunscreens in dermatology are in the prevention and management of: [1]
Spectrum of UV radiation The biologically active components of ultraviolet (UV) radiation include UVA and UVB radiation. The primary targets of UV radiation in the skin and their corresponding effects are given below: [2] UVB (290-320 nm)
UVA (320-400 nm)
Sea-level solar UV radiation is approximately 95-98% UVA and 2-5% UVB. UVC is completely absorbed by stratospheric ozone that also attenuates UVB. A given solar UVR spectrum varies with the solar zenith angle (the angle between an imaginary perpendicular line and a line from its base to the sun), which is dependent on time of day, season, and latitude. The highest UVB content is found when the sun is directly overhead with the shortest path (e.g., noon, at the equator, at high altitude). [3] Classification of Sunscreens The last FDA sunscreen monograph was issued in 1999, with a list of 16 approved sunscreen agents. It recommends that sunscreens be classified as organic and inorganic, replacing the previously used terms "chemical" and "physical", respectively. There are three commonly used nomenclatures for sunscreen agents in the world. These are the International Nomenclature Cosmetic Ingredient (INCI) name, US adopted name (USAN), and trade name. Taking avobenzone (USAN) as an example, the INCI name for avobenzone is butylmethoxydibenzoylmethane, while Parsol 1789 is one of its many trade names. [1],[3],[4],[5] A. Organic Sunscreens Organic UV filters are active ingredients that absorb UV radiation within a particular range of wavelengths, depending on their chemical structure. Once the UV filter absorbs energy, it moves from a low-energy ground state to a high-energy excited state. From this excited state, any of the following three processes may occur, depending on the ability of the filter to process the energy it has absorbed:
Organic sunscreens are further divided into UVB and UVA filters: 1. UVB filters
2. UVA filters
Note: Although avobenzone is the only sunscreen agent that has its absorption peak in the UVA1 spectrum (357 nm), making it a very effective UVA filter, it has the disadvantage of being photounstable. This is overcome, to some extent, by adding agents that photostabilize avobenzone, to the final sunscreen product. These agents include other UVA filters such as oxybenzone, UVB filters such as enzacamene (not yet FDA approved), salicylates, octocrylene, broad spectrum filters such as bemotrizinol (not yet FDA approved), and inorganic filters such as titanium dioxide and zinc oxide. 3. Newer generation broad spectrum (UVA + UVB) filters - Ecamsule (Mexoryl SX), Silatriazole (Mexoryl XL), Bemotrizinol (Tinosorb S), Bisoctrizole (Tinosorb M) Ecamsule is primarily a UVA filter, the patent for which is held by L′Orιal (sunscreens containing ecamsule are exclusive to L′Orιal and its brands). Tinosorb M is the first of a new class of UV filters that combine the properties of both UV conventional filters (organic and inorganic) - it scatters, reflects and absorbs UV light. Apart from Ecamsule, these filters are not yet US FDA approved, but are being used in other countries, such as the European Union and Canada. B.Inorganic Sunscreens
Inorganic agents function by reflecting, scattering or absorbing UV radiation. Their opaque nature and "whitening effect" are an inherent disadvantage, which may be minimized by the use of micronized or ultrafine particles. Systemic Photoprotective Agents In addition, there are several compounds that have a systemic photoprotective effect; these are sometimes referred to as "systemic sunscreens." β-carotene, antimalarials, ascorbic acid, α-tocopherols (i.e., vitamins A, C, and E), retinol, selenium, green tea polyphenols, PABA, antihistamines, aspirin, indomethacin, corticosteroids. Sunscreen-Related Indices[2],[3],[4],[6],[7],[8] Practicing dermatologists often encounter patients complaining of worsening pigmentation or recurrent polymorphous light eruption in spite of using sunscreens with "good sun protection factor (SPF)" or "SPF >50". It is important for both dermatologists and the public to be aware that a good SPF value will not protect the skin from the entire UV spectrum. In fact, in 2007, the FDA has proposed that the expansion of SPF be changed to "sunburn protection factor" to indicate that it is only an index of protection against sunburn or UVB-induced erythema, and hence does not necessarily imply UVA or broad spectrum protection. Various indices have been formulated by in vitro and in vivo methods to assess the efficacy of sunscreens with respect to specific components of the UV spectrum. These are as follows:
Grading system for SPF:
Note : It is noteworthy that a sunscreen with an SPF of 15 blocks about 93% of UVB radiation, while one with an SPF of 30 blocks about 97% of UVB radiation. This difference of 4% may make the difference between an aesthetically pleasing sunscreen and an undesirable one, as products with higher SPF generally tend to be uncomfortable due to the higher concentration of the active ingredient. [9] 2. UVA protection indices a. Japanese standard (persistent pigment darkening; in vivo method): b. Australian/New Zealand Standard (in vitro method): 8-μm layer of the product should not transmit more than 10% of radiation of 320 to 360 nm OR 20-μm layer of the product should not transmit more than 1% of radiation of 320 to 360 nm c. European Union guidelines: UVA protection factor (persistent pigment darkening method) = 1/3 of SPF AND Critical wavelength = 370 nm d. Boots star rating system (used in the United Kingdom): In vitro measurement of the ratio of a product′s UVA (320-400 nm) absorbance over its UVB (290-320 nm) absorbance is used to calculate its Boots star rating [Table - 2]. Products with better UVA absorbance have a higher Boots star rating. 3. Immune protection factor (IPF): ability of sunscreen products to prevent UV-induced immunosuppression. IPF is assessed by complex methods such as the ability of a sunscreen to inhibit either the sensitization or elicitation arm of contact or delayed-type hypersensitivity reactions to allergens such as dinitrochlorobenzene (DNCB) and nickel, respectively. IPF is considered to correlate better with the UVA-protectiveness of a sunscreen than with its SPF. [10] 4. Clothing indices UV protection factor (UPF) = the ratio of average effective UV radiation irradiance transmitted and calculated through air to the average effective UV radiation irradiance transmitted and calculated through fabric (indicates how much longer a person can stay in the sun when fabric covers the skin, erythema being the end-point). Grading of UPF:
5. Sunglass standards[12]
Categories of lenses: 0 to 4 0 Fashion spectacles (luminous transmittance 80-100%): providing some protection from UV radiation but no reduction in sunglare. 1 Fashion spectacles: providing protection from UV radiation and limited reduction of sunglare - not suitable for driving at night. 2 Sunglasses for general use: providing good protection from UV radiation and sunglare. 3 Sunglasses providing extra protection from UV radiation and sunglare. 4 Sunglasses providing a high level of protection from UV radiation and sunglare (luminous transmittance 3-8%) - must not be used when driving.
Some sunglasses may also be labeled with an eye protection factor (EPF) number, developed by the Australian Radiation Protection and Nuclear Safety Authority (ARPANSA) ranging from 1 to 10. Sunglasses labeled EPF of 9 or 10 transmit very little UV radiation. Other sunglasses may be labeled UV 400 (blocking 100% of UV) or state the amount of UV radiation blocked as a percentage such as 99.9% or 100%. The only way to assess the protection of sunglasses is to have the lenses measured, either by the manufacturer or by a properly equipped optician. Dark lenses do not automatically filter out more harmful UV radiation and blue light as compared to light lenses. Inadequate dark lenses are even more harmful than inadequate light lenses (or wearing no sunglasses at all) because they provoke the pupil to open wider. As result, more unfiltered radiation enters the eye. The only "visible" quality test for sunglasses is their fit. For the best protection, one must use wraparound, close fitting, large-lens sunglasses that help to reduce reflected UV radiation and glare that can pass around the edge of the sunglasses and reach the eyes. Sunscreen-Related Definitions[4],[7],[8] Critical wavelength: The wavelength below which 90% of the sunscreen′s UV absorbency occurs Broad spectrum sunscreen: Critical wavelength > 370 nm AND UVA protection factor > 4 Water-resistant sunscreen: Maintains the label SPF value after two sequential immersions in water for 20 min (40 min) Very water-resistant sunscreen: Maintains the label SPF value after four sequential immersions in water for 20 min (80 min) In the United States, a product that has been shown to be water-resistant or very water-resistant, can also be labeled as "sweat resistant." Recommendations for Sunscreen Application Sunscreen should be applied properly to all sun exposed areas (in a concentration of 2 mg/cm 2 ), and allowed to dry completely before sun exposure. It should be reapplied every 2 hours, and after swimming, vigorous activity, excessive perspiration, or toweling. "Teaspoon rule": [13] 3 mL (slightly more than half a teaspoon)
6 mL (slightly more than a teaspoon)
Debatable Issues 1. Sunscreen use in infants Although not known to be hazardous, the use of sunscreens is not recommended for infants younger than 6 months. [3] 2. Contact dermatitis The most common cause of contact dermatitis (photoallergy) among sunscreens is oxybenzone. [3] 3. Nanosized particles Nanosized particles range in size from 1-100 nm. Microfine forms of zinc oxide and titanium dioxide have a particle size of 20-50 nm. Nanotechnology makes inorganic sunscreens more cosmetically acceptable (less whitening of skin after application). In recent years, there have been concerns that nanoparticles can induce free radical formation in the presence of UV radiation. However, studies show that these particles remain on the surface of the skin or in the stratum corneum, and are hence safe for human use. [4] 4. Vitamin D production UVB radiation is responsible for more than 90% of vitamin D production in the skin. It is said that a few minutes exposure of the face, arms, and hands to noonday summer sunlight two or three times a week is sufficient for vitamin D synthesis. [14] There have been concerns that widespread use of sunscreens, particularly those with high SPF, may lead to a significant decrease in vitamin D production. However, there is evidence that though sunscreens can significantly reduce the production of vitamin D under very strictly controlled conditions, their normal usage does not generally result in vitamin D insufficiency. [15] In fact, vitamin D and calcium levels have been found to be relatively normal in xeroderma pigmentosum patients, in spite of strict photoprotection. [16] 5. Hormonal effects Some sunscreens (oxybenzone, avobenzone, octinoxate, padimate O) have been tested for their estrogenic/anti-androgenic properties in animal studies. [4] However, the endocrine effects of these agents remain controversial, warranting further human studies. New Sunscreen Technologies[17] SunSpheres SunSpheres are styrene/acrylate copolymers that do not absorb UV irradiation but enhance the effectiveness of the active sunscreen ingredients. The SunSphere polymer beads are filled with water, which migrates out of the particle, leaving behind tiny air-filled spheres, which have a lower refractive index (1.0) than the dried sunscreen film (1.4-1.5). As a result, scattering of UV radiation occurs, increasing the probability of contact with the active UV filters in the sunscreen. SunSpheres are also available in a powder form, and can boost SPF by 50 -70% making it possible to reduce the concentration of active ingredients. Microencapsulation Active sunscreen ingredients are entrapped within a silica shell, as a result of which, allergic or irritant reactions to the active ingredient can be minimized, and incompatible sunscreen ingredients can be safely combined, without loss of efficacy. Suggested sources for further reading: 1. Cutaneous photobiology: Fitzpatrick′s dermatology in general medicine (7 th edition) - Chapters 88 and 89. 2. Good reviews on sunscreens:
3. Systemic photoprotection
References
Copyright 2011 - Indian Journal of Dermatology, Venereology, and Leprology Indian Journal of Dermatology, Venereology, and Leprology, Vol. 77, No. 2, March-April, 2011, pp. 238-243 Residents Page Sunscreens Sowmya Kaimal, Anil Abraham Department of Dermatology, St. John's Medical College Hospital, Bangalore - 560 034, India Correspondence Address: Anil Abraham, Department of Dermatology, St. John's Medical College Hospital, Bangalore - 560 034, India, docanilabe@yahoo.co.in Code Number: dv11069 PMID: 21393968 DOI: 10.4103/0378-6323.77480 Introduction Sunscreens are a constantly evolving component of the dermatologist′s therapeutic armamentarium. This article attempts to compile some of the important aspects of sunscreens, including their classification, various indices related to photoprotection, and some of the debatable issues related to sunscreens in general. The focus is on material which is current, while at the same time being relevant for the postgraduate. Indications for the use of Sunscreens The primary use of sunscreens is to protect the skin from the short-term and long-term effects of ultraviolet radiation. In today′s scenario of procedure-centered dermatology, sunscreens have become an indispensable part of every patient′s post-procedure skin care routine. The characteristics of an ideal sunscreen are listed in [Table - 1]. The common indications for the use of sunscreens in dermatology are in the prevention and management of: [1]
Spectrum of UV radiation The biologically active components of ultraviolet (UV) radiation include UVA and UVB radiation. The primary targets of UV radiation in the skin and their corresponding effects are given below: [2] UVB (290-320 nm)
UVA (320-400 nm)
Sea-level solar UV radiation is approximately 95-98% UVA and 2-5% UVB. UVC is completely absorbed by stratospheric ozone that also attenuates UVB. A given solar UVR spectrum varies with the solar zenith angle (the angle between an imaginary perpendicular line and a line from its base to the sun), which is dependent on time of day, season, and latitude. The highest UVB content is found when the sun is directly overhead with the shortest path (e.g., noon, at the equator, at high altitude). [3] Classification of Sunscreens The last FDA sunscreen monograph was issued in 1999, with a list of 16 approved sunscreen agents. It recommends that sunscreens be classified as organic and inorganic, replacing the previously used terms "chemical" and "physical", respectively. There are three commonly used nomenclatures for sunscreen agents in the world. These are the International Nomenclature Cosmetic Ingredient (INCI) name, US adopted name (USAN), and trade name. Taking avobenzone (USAN) as an example, the INCI name for avobenzone is butylmethoxydibenzoylmethane, while Parsol 1789 is one of its many trade names. [1],[3],[4],[5] A. Organic Sunscreens Organic UV filters are active ingredients that absorb UV radiation within a particular range of wavelengths, depending on their chemical structure. Once the UV filter absorbs energy, it moves from a low-energy ground state to a high-energy excited state. From this excited state, any of the following three processes may occur, depending on the ability of the filter to process the energy it has absorbed:
Organic sunscreens are further divided into UVB and UVA filters: 1. UVB filters
2. UVA filters
Note: Although avobenzone is the only sunscreen agent that has its absorption peak in the UVA1 spectrum (357 nm), making it a very effective UVA filter, it has the disadvantage of being photounstable. This is overcome, to some extent, by adding agents that photostabilize avobenzone, to the final sunscreen product. These agents include other UVA filters such as oxybenzone, UVB filters such as enzacamene (not yet FDA approved), salicylates, octocrylene, broad spectrum filters such as bemotrizinol (not yet FDA approved), and inorganic filters such as titanium dioxide and zinc oxide. 3. Newer generation broad spectrum (UVA + UVB) filters - Ecamsule (Mexoryl SX), Silatriazole (Mexoryl XL), Bemotrizinol (Tinosorb S), Bisoctrizole (Tinosorb M) Ecamsule is primarily a UVA filter, the patent for which is held by L′Orιal (sunscreens containing ecamsule are exclusive to L′Orιal and its brands). Tinosorb M is the first of a new class of UV filters that combine the properties of both UV conventional filters (organic and inorganic) - it scatters, reflects and absorbs UV light. Apart from Ecamsule, these filters are not yet US FDA approved, but are being used in other countries, such as the European Union and Canada. B. Inorganic Sunscreens
Inorganic agents function by reflecting, scattering or absorbing UV radiation. Their opaque nature and "whitening effect" are an inherent disadvantage, which may be minimized by the use of micronized or ultrafine particles. Systemic Photoprotective Agents In addition, there are several compounds that have a systemic photoprotective effect; these are sometimes referred to as "systemic sunscreens." β-carotene, antimalarials, ascorbic acid, α-tocopherols (i.e., vitamins A, C, and E), retinol, selenium, green tea polyphenols, PABA, antihistamines, aspirin, indomethacin, corticosteroids. Sunscreen-Related Indices[2],[3],[4],[6],[7],[8] Practicing dermatologists often encounter patients complaining of worsening pigmentation or recurrent polymorphous light eruption in spite of using sunscreens with "good sun protection factor (SPF)" or "SPF >50". It is important for both dermatologists and the public to be aware that a good SPF value will not protect the skin from the entire UV spectrum. In fact, in 2007, the FDA has proposed that the expansion of SPF be changed to "sunburn protection factor" to indicate that it is only an index of protection against sunburn or UVB-induced erythema, and hence does not necessarily imply UVA or broad spectrum protection. Various indices have been formulated by in vitro and in vivo methods to assess the efficacy of sunscreens with respect to specific components of the UV spectrum. These are as follows:
Grading system for SPF:
Note : It is noteworthy that a sunscreen with an SPF of 15 blocks about 93% of UVB radiation, while one with an SPF of 30 blocks about 97% of UVB radiation. This difference of 4% may make the difference between an aesthetically pleasing sunscreen and an undesirable one, as products with higher SPF generally tend to be uncomfortable due to the higher concentration of the active ingredient. [9] 2. UVA protection indices a. Japanese standard (persistent pigment darkening; in vivo method): b. Australian/New Zealand Standard (in vitro method): 8-μm layer of the product should not transmit more than 10% of radiation of 320 to 360 nm OR 20-μm layer of the product should not transmit more than 1% of radiation of 320 to 360 nm c. European Union guidelines: UVA protection factor (persistent pigment darkening method) = 1/3 of SPF AND Critical wavelength = 370 nm d. Boots star rating system (used in the United Kingdom): In vitro measurement of the ratio of a product′s UVA (320-400 nm) absorbance over its UVB (290-320 nm) absorbance is used to calculate its Boots star rating [Table - 2]. Products with better UVA absorbance have a higher Boots star rating. 3. Immune protection factor (IPF): ability of sunscreen products to prevent UV-induced immunosuppression. IPF is assessed by complex methods such as the ability of a sunscreen to inhibit either the sensitization or elicitation arm of contact or delayed-type hypersensitivity reactions to allergens such as dinitrochlorobenzene (DNCB) and nickel, respectively. IPF is considered to correlate better with the UVA-protectiveness of a sunscreen than with its SPF. [10] 4. Clothing indices UV protection factor (UPF) = the ratio of average effective UV radiation irradiance transmitted and calculated through air to the average effective UV radiation irradiance transmitted and calculated through fabric (indicates how much longer a person can stay in the sun when fabric covers the skin, erythema being the end-point). Grading of UPF:
5. Sunglass standards[12]
Categories of lenses: 0 to 4 0 Fashion spectacles (luminous transmittance 80-100%): providing some protection from UV radiation but no reduction in sunglare. 1 Fashion spectacles: providing protection from UV radiation and limited reduction of sunglare - not suitable for driving at night. 2 Sunglasses for general use: providing good protection from UV radiation and sunglare. 3 Sunglasses providing extra protection from UV radiation and sunglare. 4 Sunglasses providing a high level of protection from UV radiation and sunglare (luminous transmittance 3-8%) - must not be used when driving.
Some sunglasses may also be labeled with an eye protection factor (EPF) number, developed by the Australian Radiation Protection and Nuclear Safety Authority (ARPANSA) ranging from 1 to 10. Sunglasses labeled EPF of 9 or 10 transmit very little UV radiation. Other sunglasses may be labeled UV 400 (blocking 100% of UV) or state the amount of UV radiation blocked as a percentage such as 99.9% or 100%. The only way to assess the protection of sunglasses is to have the lenses measured, either by the manufacturer or by a properly equipped optician. Dark lenses do not automatically filter out more harmful UV radiation and blue light as compared to light lenses. Inadequate dark lenses are even more harmful than inadequate light lenses (or wearing no sunglasses at all) because they provoke the pupil to open wider. As result, more unfiltered radiation enters the eye. The only "visible" quality test for sunglasses is their fit. For the best protection, one must use wraparound, close fitting, large-lens sunglasses that help to reduce reflected UV radiation and glare that can pass around the edge of the sunglasses and reach the eyes. Sunscreen-Related Definitions[4],[7],[8] Critical wavelength: The wavelength below which 90% of the sunscreen′s UV absorbency occurs Broad spectrum sunscreen: Critical wavelength > 370 nm AND UVA protection factor > 4 Water-resistant sunscreen: Maintains the label SPF value after two sequential immersions in water for 20 min (40 min) Very water-resistant sunscreen: Maintains the label SPF value after four sequential immersions in water for 20 min (80 min) In the United States, a product that has been shown to be water-resistant or very water-resistant, can also be labeled as "sweat resistant." Recommendations for Sunscreen Application Sunscreen should be applied properly to all sun exposed areas (in a concentration of 2 mg/cm 2 ), and allowed to dry completely before sun exposure. It should be reapplied every 2 hours, and after swimming, vigorous activity, excessive perspiration, or toweling. "Teaspoon rule": [13] 3 mL (slightly more than half a teaspoon)
6 mL (slightly more than a teaspoon)
Debatable Issues 1. Sunscreen use in infants Although not known to be hazardous, the use of sunscreens is not recommended for infants younger than 6 months. [3] 2. Contact dermatitis The most common cause of contact dermatitis (photoallergy) among sunscreens is oxybenzone. [3] 3. Nanosized particles Nanosized particles range in size from 1-100 nm. Microfine forms of zinc oxide and titanium dioxide have a particle size of 20-50 nm. Nanotechnology makes inorganic sunscreens more cosmetically acceptable (less whitening of skin after application). In recent years, there have been concerns that nanoparticles can induce free radical formation in the presence of UV radiation. However, studies show that these particles remain on the surface of the skin or in the stratum corneum, and are hence safe for human use. [4] 4. Vitamin D production UVB radiation is responsible for more than 90% of vitamin D production in the skin. It is said that a few minutes exposure of the face, arms, and hands to noonday summer sunlight two or three times a week is sufficient for vitamin D synthesis. [14] There have been concerns that widespread use of sunscreens, particularly those with high SPF, may lead to a significant decrease in vitamin D production. However, there is evidence that though sunscreens can significantly reduce the production of vitamin D under very strictly controlled conditions, their normal usage does not generally result in vitamin D insufficiency. [15] In fact, vitamin D and calcium levels have been found to be relatively normal in xeroderma pigmentosum patients, in spite of strict photoprotection. [16] 5. Hormonal effects Some sunscreens (oxybenzone, avobenzone, octinoxate, padimate O) have been tested for their estrogenic/anti-androgenic properties in animal studies. [4] However, the endocrine effects of these agents remain controversial, warranting further human studies. New Sunscreen Technologies[17] SunSpheres SunSpheres are styrene/acrylate copolymers that do not absorb UV irradiation but enhance the effectiveness of the active sunscreen ingredients. The SunSphere polymer beads are filled with water, which migrates out of the particle, leaving behind tiny air-filled spheres, which have a lower refractive index (1.0) than the dried sunscreen film (1.4-1.5). As a result, scattering of UV radiation occurs, increasing the probability of contact with the active UV filters in the sunscreen. SunSpheres are also available in a powder form, and can boost SPF by 50 -70% making it possible to reduce the concentration of active ingredients. Microencapsulation Active sunscreen ingredients are entrapped within a silica shell, as a result of which, allergic or irritant reactions to the active ingredient can be minimized, and incompatible sunscreen ingredients can be safely combined, without loss of efficacy. Suggested sources for further reading: 1. Cutaneous photobiology: Fitzpatrick′s dermatology in general medicine (7 th edition) - Chapters 88 and 89. 2. Good reviews on sunscreens:
3. Systemic photoprotection
References
Copyright 2011 - Indian Journal of Dermatology, Venereology, and Leprology The following images related to this document are available:Photo images[dv11069t2.jpg] [dv11069t1.jpg] |
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