The most important class of sunscreens are those, which operate by absorbing the erythemal ultraviolet radiation. The ideal properties necessary for sunscreen are:
- It must be effective in absorbing erythmogenic radiation in the 290- 320 nm range without breakdown, which would reduce its efficiency or give rise to toxic or irritant compounds.
- It must allow full transmission in the 300-400 nm range to permit the maximum tanning effect.
- It must be nonvolatile and resistant to water and perspiration.
- It must possess suitable solubility characteristics to allow the formulation of a suitable cosmetic vehicle to accommodate the requisite amount of sun screening.
- It must be non-odorous or at least sufficiently mild to be acceptable to the user and be satisfactory in other relevant physical characteristics such as stickiness, etc.
- It must be nontoxic, nonirritant, and non-sensitizing.
- It must be highly effective at low concentrations.
- It must not require too frequent re-application to be effective.
- It must be capable of retaining its protective capacity for several hours.
- It must be stable under conditions of use.
- It must be non-stain clothing.
Classification of sunscreens
1. Classification of sunscreens based on applications
(A) Topical
(i) Organic:
- UV-A filters: Benzophenones, Avobenzone, Meradimate, Bisdisulizole disodium, Diethyl aminohydroxy benzoyl hexylbenzoate, Methyl anthraniline.
- UV-B filters: PABA derivatives, Cinnamate, Salicylates, Octocrylene, Ensulizole, Ethylhexyl triazone
Broad spectrum filters: Ecamsule, Silatriazole, Bemotrizinol, Bisoctrizole.
(ii) Inorganic: Zinc oxide, Titanium dioxide, others (iron oxide, kaolin, calamine, ichthammol, talc)
(B) Systemic
β-carotene, Ascorbic acids, α-tocopherols, Retinol, Selenium, Green tea polyphenols, PABA, Antihistamines, Aspirin, Indomethacin, Corticosteroids
2. Classification of sunscreens based on chemical nature
(i) Inorganic (physical) sunscreens
Ex: Zinc oxide, Titanium dioxide
(ii) Organic sunscreens
Ex: Benzo phenone derivatives, PABA and its derivatives, Menthyl anthranilate, Ethyl-hexyl-salicylate, Dibenzoyl methane derivatives, Benzalmalonate, Phenyl benzimidazole derivatives.
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