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Chapter: Essential pharmacology : Drugs Acting On Skin And Mucous Membranes

Sunscreens are substances that protect the skin from harmful effects of exposure to sunlight.



Sunscreens are substances that protect the skin from harmful effects of exposure to sunlight.


Chemical  Sunscreens


They absorb and scatter UV rays that are responsible for sunburn and phototoxicity, but allow longer wave lengths to penetrate, so that tanning occurs.


Efficacy of a sunscreen formulation is quantified by its ‘Sun protection factor’ (SPF) which is the ratio of the dose of UVB radiation that will produce minimal erythema on protected skin to the dose required for the same on unprotected skin. Most commercial preparations have a SPF of 15. Period for which they remain effective depends on the vehicle.


Paraaminobenzoic acid (PABA) and its esters: glyceryl mono amino benzoate. They absorb UVB (290–320 nm). PABA is used as 5% solution in alcohol/propylene glycol (PABALAK) or as 10% cream (PARAMINOL).


Benzophenones (such as oxybenzone 2–6%) block UVA (320–400 nm); are highly protective; thus higher concentrations prevent tanning also.


Cinnamates (such as octyl methoxy cinnamate) are included in sunscreens.


SUNSHIELD: Octyl methoxy cinnamate 5%, vit E 0.25% lotion. EUKROMASG: Oxybenzone 3%, Octylmethoxy cinnamate 5%, hydroquinone 2% cream.




Chemical sunscreens are used as adjuncts in vitiligo therapy, drug induced phototoxicity and to facilitate tanning while preventing sunburn. There is some evidence that they can prevent skin cancer and premature ageing of skin.


Physical Sunscreens


Heavy petroleum jelly, titanium dioxide, zinc oxide and calamine are opaque substances that stop and scatter not only UV but also visible light. They are also called ‘sun shades’ and have to be applied as a thick lotion/cream which may be cosmetically disagreeable. They withhold longer wave lengths also, which are mostly involved in photoallergy. Not only sunburn, but tanning as well is prevented.


Chloroquine taken orally is effective in actinic eruptions, but should be reserved for severe cases only.


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