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