SUNSCREEN & SUNSCREEN AGENTS : A REVIEW

About Authors:
*M.C.Sai HariKishan, C.P.Meher, S.M.Ahmed
Maheshwara Institute Of Pharmacy, Chitkul, Isnapur ,
Patancheru, Hyderabad-502307
*hari_mc@yahoo.com

ABSTRACT:
Sunscreen agents are used to prevent sunburn. Limiting the exposure to the sun and using sunscreen agents when in the sun may help prevent early wrinkling of the skin and skin cancer. There are two kinds of sunscreen agents: chemical and physical. Chemical sunscreen agents protect from the sun by absorbing the ultraviolet (UV) and visible sun rays, while physical sunscreen agents reflect, scatter, absorb, or block these rays. Sunscreen agents often contain more than one ingredient. For example, products may contain one ingredient that provides protection against the ultraviolet A (UVA) sun rays and another ingredient that protects from the ultraviolet B (UVB) sun rays, which are more likely to cause sunburn than the UVA sun rays. Ideally, coverage should include protection against both UVA and UVB sun rays. The sun protection factor (SPF) that find on the label of these products tells the minimum amount of UVB sunlight that is needed with that product to produce redness on sunscreen-protected skin as compared with unprotected skin. Sunscreen products with high SPFs will provide more protection against the sun.The presented review article is concern with discussion on the sunscreen agents.

REFERENCE ID: PHARMATUTOR-ART-1664

INTRODUCTION:
Sunscreen(also commonly known as sunblock, sun tan lotion, sun screen, sunburn cream or block out) is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet (UV) radiation on the skin exposed to sunlight and thus helps protect against sunburn. Skin-lightening products have sunscreen to protect lightened skin because light skin is more susceptible to sun damage than darker skin. Depending on the mode of action sunscreens can be classified into physical sunscreens (i.e., those that reflect the sunlight) or chemical sunscreens (i.e., those that absorb the UV light). Sunscreens have traditionally been divided into chemical absorbers and physical blockers on the basis of their mechanism of action. Chemical sunscreens are generally aromatic compounds conjugated with a carbonyl group. These chemicals absorb high-intensity UV rays with excitation to a higher energy state. The energy lost results in conversion of the remaining energy into longer lower energy wavelengths with return to ground state. Physical blockers reflect or scatter UVR. Recent research indicates that the newer microsized forms of physical blockers may also function in part by absorption. Sometimes referred to as nonchemical sunscreens, they may be more appropriately designated as inorganic particulate sunscreen ingredients. Allowable ingredients and maximum allowable concentrations, as listed in the FDA monograph, are shown in the Table below. Sunscreen ingredients can also be classified by the portion of UVR that they effectively absorb. Encouraging photoprotection is the leading preventative health strategy used by physicians involved in skin care. Although sun avoidance is most desirable, outdoor occupations and lifestyles make total avoidance impossible for many individuals. The regular use of sunscreens represents a practical compromise in this regard. Sunscreens prevent the formation of squamous cell carcinomas in animals. In humans, the regular use of sunscreens has been shown to reduce actinic keratoses, solar elastosis, and squamous cell carcinoma.The routine use of sunscreens may also reduce melanoma risk.Drug photosensitization and photo-induced or photo-aggravated dermatoses may be prevented with sunscreen use, especially with products that offer better blockage in the UV-A range.

PRECAUTIONS:
Sunscreen products are available with and without doctor's prescription. If we using this medicine without a prescription, carefully should read and follow any precautions on the label. If rash or irritation develops, stop using the sunscreen and check with your doctor. Sunscreen agents containing aminobenzoic acid, lisadimate, padimate O, or roxadimate may discolor and stain light-colored fabrics yellow. In addition to using sunscreen agents, it is advisable to minimize exposure to the sun from 10 a.m. to 2 p.m. (11 a.m. to 3 p.m. daylight savings time) when the sun is at its strongest. Take extra precautions also on cloudy or overcast days and around reflective surfaces such as concrete, sand, snow, or water, since these surfaces can reflect the sun's damaging rays. Wear protective clothing including a hat, long-sleeved shirt, and long pants. Sunglasses also should be worn to avoid sun damage to the eyes (cataract formation). Avoid sunlamps and tanning parlors because these can damage the skin and eyes as direct sunlight can. The following are skin types (complexions) and the appropriate sunscreen agent that should be used:

Very fair; always burns easily; rarely tans—Use SPF 20 to 30.
Fair; always burns easily; tans minimally—Use SPF 12 to 20.
Light; burns moderately; tans gradually (light brown)—Use SPF 8 to 12.
Medium; burns minimally; always tans well (moderate brown)—Use SPF 4 to 8.
Dark; rarely burns; tans profusely (dark brown)—Use SPF 2 to 4.

PROPER USE
Sunscreen agents are for external use only. These products usually come with patient directions. Carefull reading is needed before using any product. In choosing the sunscreen product, following point are considered for better effectiveness.

1.Type of Activity—Take precautions when you are in places of higher elevations (mountains) or on reflective surfaces (concrete, sand, snow, or water), as these may increase the likelihood of sun damage to the skin. Use a sunscreen with ultraviolet A/ultraviolet B (UVA/UVB) coverage and with a sun protection factor (SPF) of 15 or higher. Activities that make you sweat, such as outdoor jobs (gardeners, construction workers), outdoor sports (tennis) or exercise, prolonged sunbathing, or water sports such as swimming, water-skiing, or wind surfing, may result in the removal of the sunscreen agent from the skin. Use a water-resistant or waterproof sunscreen agent with SPF of 15 or more. When possible, also wear a hat, long-sleeved shirt, long pants, and UV-opaque sunglasses. Wearing UV-opaque sunglasses when you are in the sun is also necessary because the sun rays can cause cataracts.

2.Age—Do not use sunscreen agents on infants younger than 6 months of age. For children 6 months of age and older, use a lotion form of sunscreen with broad spectrum and SPF of 15 or higher. Avoid using alcohol-based sunscreen products for this age group.

3.Site of application—For the ear and nose, use a physical sunscreen agent. For the lips, use a gel-based lip sunscreen or lip balm.

4.Skin condition—If your skin is dry, use a cream or lotion form of sunscreen agent. If your skin is oily, use an alcohol or gel-based sunscreen. Avoid using alcohol-based sunscreens on eczematous or inflamed skin.

SUNSCREEN AGENTS
Various type of reagents are used in the preparation of the sunscreen products. some of the important reagents are briefly described below.

4-Aminobenzoic acid: It also known as para-aminobenzoic acid or PABA because the number 4 carbon in the benzene ring is also known as the para position.it is an organic compound with the formula H₂NC₆H₄CO₂H. PABA is a white grey crystalline substance that is only slightly soluble in water. It consists of a benzene ring substituted with an amino group and a carboxyl group.

The potassium salt is used as a drug against fibrotic skin disorders, such as Peyronie's disease¹ PABA is also occasionally used in pill form by sufferers of irritable bowel syndrome to treat its associated gastrointestinal symptoms, and in nutritional epidemiological studies to assess the completeness of 24-hour urine collection for the determination of urinary sodium, potassium, or nitrogen levels.

Avobenzone : it is an oil soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays. It is a dibenzoylmethane derivative. Avobenzone exists in the ground state as a mixture of the enol and keto forms, favoring the chelated enol.²Its ability to absorb ultraviolet light over a wider range of wavelengths than many organic sunscreen agents has led to its use in many commercial preparations marketed as "broad spectrum" sunscreens. Avobenzone has an absorption maximum of 357 nm.³

1-(4-Methoxyphenyl)-3-(4-tert-butylphenyl)propane-1,3-dione

Bemotrizinol: it is an oil-soluble organic compound that is added to sunscreens to absorb UV rays. Bemotrizinol is a broad-spectrum UV absorber, absorbing UVB as well as UVA rays. It has two absorption peaks, 310 and 340 nm. It is highly photostable. Even after 50 MEDs (minimal erythemal doses), 98.4% remains intact. It helps prevent the photodegradation of other sunscreen actives like avobenzone.

2,2′-[6-(4-methoxyphenyl)- 1,3,5-triazine-2,4-diyl] bis{5-[(2-ethylhexyl)oxy]phenol}

Bisdisulizole disodium: it is a water soluble organic compound which is added to sunscreens to absorb UVA rays. Bisdisulizole disodium is not approved in the United States by the FDA, but it has been approved in the European Union since the year 2000 and other parts of the world.⁴

disodium 2,2'-(1,4-phenylene)bis(6-sulfo-1H-benzimidazole-4-sulfonate)

Bisoctrizole : it is a benzotriazole-based organic compound that is added to sunscreens to absorb UV rays. Bisoctrizole is a broad-spectrum ultraviolet radiation absorber, absorbing UVB as well as UVA rays. It also reflects and scatters UV. Bisoctrizole is a hybrid UV absorber, the only organic UV filter produced and microfine organic particles (< 200 nm)⁵ like microfine zinc oxide and titanium dioxide. Where other organic UV absorbers need to be dissolved in either the oil or water phase, bisoctrizole dissolves poorly in both. Bisoctrizole is added to the water phase of a sunscreen as a 50% suspension, whereas mineral micropigments are usually added to the oil phase. The bisoctrizole particles are stabilized by the surfactant decyl glucoside. Bisoctrizole shows very little photodegradation and has a stabilizing effect on other UV absorbers, octyl methoxycinnamate (octinoxate) in particular. When formulated into a sunscreen, bisoctrizole has minimal skin penetration.⁶Unlike some other organic sunscreen actives, it shows no estrogenic effects in vitro.⁷

2,2′-methanediylbis[6-(2H-benzotriazol-2-yl)-4-(2,4,4-trimethylpentan-2-yl)phenol]

Cerium(IV) oxide: it also known as ceric oxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare earth metal cerium. It is a pale yellow-white powder with the chemical formula CeO₂. Cerium(IV) oxide is used in ceramics, to sensitize photosensitive glass, as a catalyst and as a catalyst support, to polish glass and stones, in lapidary as an alternative to "jeweller's rouge". It is also known as "optician's rouge". It is also used in the walls of self-cleaning ovens as hydrocarbon catalyst during the high-temperature cleaning process. While it is transparent for visible light, it absorbs ultraviolet radiation strongly, so it is a prospective replacement of zinc oxide and titanium dioxide in sunscreens, as it has lower photocatalytic activity. However, its thermal catalytic properties have to be decreased by coating the particles with amorphous silica or boron nitride. The use of these nanoparticles, which can penetrate the body and reach internal organs, has been criticized as unsafe. Cerium oxide has found use in infrared filters, as an oxidizing species in catalytic converters and as a replacement for thorium dioxide in incandescent mantles^.8

Cinoxate: it is an organic compound used as an ingredient in some types of sunscreens. It is an ester formed from methoxycinnamic acid and 2-ethoxyethanol. It is a slightly yellow viscous liquid that is insoluble in water, but miscible with alcohols, esters, and vegetable oils. It protects skin against the sun by absorbing UV-Aand UV-B rays⁹

2-Ethoxyethyl 3-(4- methoxyphenyl)propenoate

Dibenzylideneacetone or dibenzalacetone: it is an organic compound with the formula C₁₇H₁₄O. It is a bright-yellow solid insoluble in water, but soluble in ethanol. Dibenzylideneacetone is used as a sunscreen component and as a ligand in organometallic chemistry, for instance in tris (dibenzylideneacetone) dipalladium (0). In this case, it is a labile ligand that is easily displaced by stronger ligands like triphenylphosphine, hence it serves a useful entry point into palladium(0) chemistry¹⁰

(1E,4E)-1,5-diphenylpenta-1,4-dien-3-one

Diethylamino hydroxybenzoyl hexyl benzoate: it is an organic compound used in sunscreens to absorb UVA radiation. DHHB has an absorption maximum of 354 nm. DHHB has excellent photostability and compatibility with other UV absorbers and other cosmetic ingredients. DHHB has been approved for the use in sunscreens in the European Union since 2005 with a maximum of 10 per cent and is also approved in South America, Mexico, Japan and Taiwan.In the United States it can be used for product protection.¹¹

Hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate

Dioxybenzone(benzophenone-8) : it is an organic compoundused in sunscreento block UVB and short-wave UVA (ultraviolet) rays. It is a derivative of benzophenone. It is a yellow powder with a melting point of 68 °C. It is insoluble in water, but moderately soluble in ethanoland isopropanol⁹

(2-Hydroxy-4-methoxyphenyl)- (2-hydroxyphenyl)methanone

Drometrizole trisiloxane: it is a lipophilic benzotriazole derivative and used in sunscreens to absorb UV radiation. It is a broad-spectrum UV absorber with two absorption peaks, one at 303 nm (UVB) and one at 344 nm (UVA). Drometrizole trisiloxane and ecamsule are often used together, because they show a synergistic effect in protection.¹²

2-(2H-Benzotriazol-2-yl)-4-methyl-6-[2-methyl-3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]-1-disiloxanyl]propyl]phenol

Ecamsule: it is an organic compound which is added to many sunscreens to filter out UVA rays. It is a benzylidene camphor derivative, many of which are known for their excellent photostability.Although there are a few different UV absorbers with the trade name Mexoryl, only two of them are widely used where approved. Mexoryl SX (water soluble) and Mexoryl XL (INCI Drometrizole trisiloxane, oil soluble). Together they show a synergistic effect in protection.

[(3Z)-3-[[4-[(Z)-[7,7-Dimethyl-2-oxo-1-(sulfomethyl)-3-bicyclo[2.2.1]heptanylidene]methyl]phenyl]methylidene]-7,7-dimethyl-2-oxo-1-bicyclo[2.2.1]heptanyl]methanesulfonic acid

Homosalate: it is an organic compound used in some sunscreens. It is an ester formed from salicylic acid and 3,3,5-trimethylcyclohexanol, a derivative of cyclohexanol. The salicylic acid portion of the molecule absorbs ultraviolet rays with a wavelength from 295 nm to 315 nm, protecting the skin from sun damage. The hydrophobic cyclohexanol portion provides greasiness that prevents it from dissolving in water⁹

3,3,5-Trimethylcyclohexyl 2-hydroxybenzoate

4-Methylbenzylidene camphor(4-MBC): it is an organic camphor derivative that is used in the cosmetic industry for its ability to protect the skin against UV, specifically UV B radiation. As such it is used in sunscreen lotions and other skincare products claiming a SPF value¹³

(3E)-1,7,7-Trimethyl-3-[(4-methylphenyl)methylene]-2-norbornanone

Octocrylene: it is an organic compound used as an ingredient in sunscreens and cosmetics. It is an ester formed by the condensation of a diphenylcyanoacrylate with 2-ethylhexanol. It is a viscous, oily liquid that is clear and colorless. The extended conjugation of the acrylate portion of the molecule absorbs UVB and short-wave UVA (ultraviolet) rays with wavelengths from 280 to 320 nm,¹⁴ protecting the skin from direct DNA damage. The ethylhexanol portion is a fatty alcohol, adding emollient and oil-like (water resistant) properties. This organic compound can penetrate into the skin where it acts as a photosensitizer. This results in an increased production of free radicals under illumination. Free radicals are known to induce indirect DNA damage and an increased concentration of free radicals might have contributed to the increased incidence of malignant melanoma in sunscreen-users compared to non-users

2-ethylhexyl 2-cyano-3,3- diphenyl-2-propenoate

Octyl methoxycinnamate or octinoxate: it is an organic compound that is an ingredient in some sunscreens and lip balms. It is an ester formed from methoxycinnamic acid and 2-ethylhexanol. It is a clear liquid that is insoluble in water. Its primary use is in suncreens and other cosmetics to absorb UV-B and UV-A rays from the sun, protecting the skin from damage. It is also used to reduce the appearance of scars¹⁵

Octyl salicylate, or 2-ethylhexyl salicylate: it is an organic compound used as an ingredient in sunscreens and cosmetics to absorb UVB (ultraviolet) rays from the sun. It is an ester formed by the condensation of a salicylic acid with 2-ethylhexanol. It is a colorless oily liquid with a slight floral odor. The salicylate portion of the molecule absorbs ultraviolet light, protecting skin from the harmful effects of exposure to sunlight. The ethylhexanol portion is a fatty alcohol, adding emollient and oil-like (water resistant) properties.

2-ethylhexyl 2-hydroxybenzoate

Oxybenzone: it is an organic compound used in sunscreens. It forms colorless crystals that are readily soluble in most organic solvents. It is used as an ingredient in sunscreen and other cosmetics because it absorbs UVB and short-wave UVA (ultraviolet) rays.⁹Oxybenzone was one of the first compounds incorporated into sunscreen formulations to offer enhanced UVA protection because its absorption spectrum extends to less than 350 nm. Oxybenzone's ability to absorb UV rays is due to a variety of molecular interactions. In this compound, both of the phenyl rings can interact with the C=O group through inductive effects and mesomeric effects. The overlapping of the π bonds of both phenyl rings and that of the C=O creates a completely conjugated molecule as evidenced by the MO diagram. This causes the C=O group to lose part of its individual character as it integrates with the two phenyl rings. This stabilizes the system due to the transference of electron deficiency from the carbon of the carbonyl towards three of the carbons of the phenyl rings.¹⁶

(2-Hydroxy-4-methoxyphenyl)-phenylmethanone

Padimate A: it is an organic compoun that is an ingredient in some sunscreens. It is an ester derivative of PABA. This aromatic chemical absorbs ultraviolet rays thereby preventing sunburn. However, it's chemical structure and behaviour is similar to an industrial free radical generator.¹⁷ In Europe this chemical was withdrawn in 1989 for unstated reasons.^[1]In the US it was never approved for use in sunscreens.

3-methylbuthyl 4-(dimethylamino)benzoate

Padimate O : it is an organic compoundrelated to the water-soluble compound PABA(4-aminobenzoic acid) that is used as an ingredient in some sunscreens. This yellowish water-insoluble oily liquid is an esterformed by the condensationof 2-ethylhexanolwith dimethylaminobenzoic acid. Other names for padimate O include 2-ethylhexyl 4-dimethylaminobenzoate, Escalol 507, octyldimethyl PABA, and OD-PABA¹⁸

2-ethylhexyl 4-(dimethylamino)benzoate

Phenylbenzimidazole sulfonic acid (C₁₃H₁₀N₂O₃S): it is a common sunscreen agent. Phenylbenzimidazole sulfonic acid is primarily a UVB protecting agent providing only minimal UVA protection. The scope of UVB is 290 to 340 nanometers whereas the UVA range is 320 to 400 nanometers.For better UVA protection, it must be paired with avobenzone, titanium dioxide, or zinc oxide; outside of the United States it can also be paired with Tinosorb and Mexoryl ^.Because phenylbenzimidazole sulfonic acid is water-soluble, it has the characteristic of feeling lighter on skin. As such, it is often used in sunscreen lotions or moisturizers whose aesthetic goal is a non-greasy finish.The free acid is poorly soluble in water, so it is only used as its soluble salts.

2-Phenyl-3H-benzimidazole-5-sulfonic acid

Sulisobenzone(benzophenone-4): it is an ingredient in some sunscreenswhich protects the skin from damage by UVB⁹ and short-wave UVA ultraviolet light.Its sodium salt, sulisobenzone sodium, is also referred to as benzophenone-5.

4-Hydroxy-2-methoxy-5-(oxo-phenylmethyl)benzenesulfonic acid

Titanium dioxide: it also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it is sourced from ilmenite, rutile and anatase. It has a wide range of applications, from paint to sunscreen to food colouring. When used as a food colouring, it has E number E171. In cosmetic and skin care products, titanium dioxide is used as a pigment, sunscreen and a thickener. It is also used as a tattoo pigment and in styptic pencils. Titanium dioxide is produced in varying particle sizes, oil and water dispersible, and with varying coatings for the cosmetic industry. This pigment is used extensively in plastics and other applications for its UV resistant properties where it acts as a UV absorber, efficiently transforming destructive UV light energy into heat. Titanium dioxide is found in almost every sunscreen with a physical blocker because of its high refractive index, its strong UV light absorbing capabilities and its resistance to discolouration under ultraviolet light. This advantage enhances its stability and ability to protect the skin from ultraviolet light. Nano-scaled titanium dioxide particles are primarily used in sun screen lotion because they scatter visible light less than titanium dioxide pigments while still providing UV protection.[24] Sunscreens designed for infants or people with sensitive skin are often based on titanium dioxide and/or zinc oxide, as these mineral UV blockers are believed to cause less skin irritation than other UV absorbing chemicals. The titanium dioxide particles used in sunscreens have to be coated with silica or alumina, because titanium dioxide creates radicals in the photocatalytic reaction. These radicals are carcinogenic, and could damage the skin¹⁹

Umbelliferone: it is also known as 7-hydroxycoumarin, hydrangine, skimmetine, and beta-umbelliferone, is a widespread natural product of the coumarin family. It absorbs ultraviolet light strongly at several wavelengths. Despite several indications that this chemical is photomutagenic, it is used in sunscreens. Umbelliferone has been reported to have antioxidant properties.

7-hydroxycoumarin, hydrangine, skimmetine, beta-umbelliferone

The ultraviolet activity of umbelliferone led to its use as a sunscreen agent, and an optical brightener for textiles. It has also been used as a gain medium for dye lasers²⁰. Umbelliferone can be used as a fluorescence indicator for metal ions such as copper and calcium. It acts as a pH indicator in the range 6.5-8.9.

CONCLUSION:
Sunscreen is a lotion, spray, or gel that absorbs or reflects some of the sun’s ultraviolet (UV) radiation, and helps protect against sunburn. Some cosmetic products also contain ingredients that may help to protect skin. All sunscreens are rated with a SPF (Sun Protection Factor) number. SPF tells how long you may be exposed to UVB light (NOT UVA light) before you burn. An SPF of 15 means that can be exposed to sunlight 15 times longer than unprotected skin before burning. They consist of a delivery vehicle containing one or more sunscreen active ingredients. When applied to the skin, these sunscreen actives intercept solar ultraviolet (UV) rays before they can damage the underlying skin. However, while conceptually simple, a detailed analysis reveals that sunscreen formulations are quite complex, requiring careful selection of sunscreen active and vehicle components to control multiple performance and in-use parameters.

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