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Sunscreen
Sunscreen
Sunscreens
• Sunscreens
Electromagnetic spectrum
Melanin
• Melanin
Melanin
• Melanin is a natural dark brown pigment present in the skin.
• The photochemical reactions with which we have the most direct sensory experience are those that cause skin to tan and burn due to more production of the melanin.
• Excess exposure to Sun’s UV radiation causes skin damage and skin cancer.
Melanin
• The infrared radiation from the sun that strikes your body is felt as warmth.
• .
Vitamin D
• The ultraviolet radiation causes photochemical reactions to occur.
• 7-dehydrocholesterol converted to vitamin D, the "sunshine" vitamin
Vitamin D
Melanin
• The uv radiation activates specific enzymes (certain proteins that have specific biochemical tasks) to photochemically convert tyrosine, an amino acid component of skin proteins, into the compound melanin.
Melanin
• Melanin is brown in color and is efficient at absorbing uv radiation
• the melanin sacrificially absorbs the uv radiation, thereby protecting the skin somewhat from further uv damage
• such as burning or activation of skin cancer formation.
Sunscreen Compounds
• Sunscreens sacrificially absorb uv radiation,
• in the same way as melanin,
• protect the skin against uv damage.
How does sunscreen work?
• By combining organic and inorganic active ingredients.
• Inorganic ingredients like zinc oxide or titanium oxide reflect or scatter ultraviolet (UV) radiation.
• Among the inorganics, zinc oxide offers much better UV-A protection than TiO2.
Inorganic Sunscreen
• Newest TiO2 has a particle size distribution between 40 and 50 nm, offering not only good UV protection
• also avoids the occurrence of large particles that give a whitening effect.
• The TiO2-coated mica pigment complements and enhances light skin tones and gives a more "natural" appearance to a beach sunscreen,
Sunscreen
• Organic ingredients like octyl methoxycinnamate (OMC) or oxybenzone absorb UV radiation, dissipating it as heat.
Sunscreen
• Formulators often combine inorganic and organic sunscreens for a synergistic effect
• capable of achieving very high SPF--sun protection factor--ratings.
Sunscreen
• Organic ingredients like octyl methoxycinnamate (OMC) or oxybenzone absorb UV radiation, dissipating it as heat.
• potential endocrine disrupters
Sunscreen
• Some sunscreens protect us from the two types of damaging UV radiation: UV-A and UV-B.
• Both UV-A and UV-B cause sunburns and damaging effects such as skin cancer.
UV Radiations
• three types of wavelengths:• UV-A: near UV region
wavelength • Not absorbed by the ozone. It
penetrates the skin deeper than UV-B. 320-400 nm
• Tanning
UV-B• Responsible for sunburns.
• It is partially blocked by the ozone layer.
• 280-320nm
UV-C
• Far UV .
• totally absorbed by the earth's atmosphere;
• we encounter it only from artificial radiation sources. 200 – 280 nm
Factors affecting UV Radiations
• Stratospheric Ozone
• Time of the day
• Time of the year
• Latitude
• Altitude
• Weather conditions
Purchasing Sunscreen
• the Sun Protection Factor or SPF measures how effectively the sunscreen formula limits skin exposure to UV-B rays that burn the skin.
•
Sunscreen
• The higher the SPF the more protection the sunscreen will provide against UV-B rays.
• SPF does not measure UV-A.•
Sunscreen
• If you are looking for UV-A protection,
• purchase a product that has broad-spectrum protection.
Sunscreen Compounds
• Uv light also produces photochemical reactions within the eye that produce cataracts and retinal damage.
• Dark sunglasses do not necessarily filter out uv radiation.
• Those that are made specifically to filter out the damaging uv radiation should always be used.
PABA
• The first sunscreen developed, para-aminobenzoic acid (PABA),
• fell out of use because it stained clothing and was found to cause allergic reactions in some people.
avobenzone
known as Parsol 1789, as a UVA absorber.
Butyl methoxy dibenzoyl- methane
PABA
• the para-aminobenzoic acid esters (primarily octyl dimethyl para-aminobenzoic acid) are commonly used in many formulations
• and have not been associated with the solubility and sensitivity problems of PABA
PABA
• Para-Aminobenzoic Acid
• serve as a nutrient for the intestinal tract's numerous microorganisms.
•
PABA
• increases the intestinal synthesis of other B vitamins, particularly of folic acid, of which it is a structural unit.
Folic acid showing PABA
PABA ester
can eliminate the irritation and staining problems.
PABA
• Contains conjugated carbon: single and double bonds
• The wavelength of radiation absorbed depends on the number of conjugated double bonds
• Wavelength max for PABA ~ 265 nm
• Wavelength max for Vit A ~ 500 nm 11 double bonds
PABA
• PABA absorbs strongly ~240-290 nm
• Maximum absorption ~ 265nm
• Protects in Far UV 200-280 nm
• Does not protect ~310 nm
• burning of skin
• Need more effective mixture of compounds
Retinal 11 conjugated double bonds; max 500 nm
Greater the number of double bonds; longer the wavelength absorbed
Sunscreen Compounds
• 2-ethylhexyl-p-methoxycinnamate
• 2. oxybenzone
Sunscreen
• 4-MBC potential endocrine disrupters
Suncreen
• Sitting behind the window
• Reddening of the skin /not a sun burn
• Glass does not transmit much light of wavelength below 350 nm
When To Apply Sunscreen
• Apply sunscreen approximately 30 minutes before being in the sun (for best results) so that it can be absorbed by the skin and less likely to wash off when you perspire.
• Remember to reapply sunscreen after swimming or strenuous exercise.
• Apply sunscreen often throughout the day if you work outdoors, and wear hats and protective clothing.
How To Apply Sunscreen
• Shake well before use to mix particles that might be clumped up in the container. Consider using the new spray-on or stick types of sunscreen.
• Be sure to apply enough sunscreen. As a rule of thumb, use an ounce (a handful) to cover your entire body.
• Use on all parts of your skin exposed to the sun, including the ears, back, shoulders, and the back of the knees and legs.
• Apply thickly and thoroughly. • Be careful when applying sunscreen around the
eyes.
What is an SPF?
• SPF stands for Sun Protection Factor. Sunscreens are rated or classified by the strength of their SPF. The SPF numbers on the packaging can range from as low as 2 to greater than 50. These numbers refer to the product’s ability to deflect the sun’s burning rays.
SPF
• The sunscreen SPF rating is calculated by comparing the amount of time needed to produce a sunburn on sunscreen protected skin
• to the amount of time needed to cause a sunburn on unprotected skin.
SPF
• if a sunscreen is rated SPF 2 and a fair-skinned person who would normally turn red after ten minutes of exposure in the sun uses it,
• it would take twenty minutes of exposure for the skin to turn red.
• A sunscreen with an SPF of 15 would allow that person to multiply that initial burning time by 15, which means it would take 15 times longer to burn, or 150 minutes.
SPF
• PF Math
• SPF Number x Time to Burn Without Sun Protection = Time to Burn while wearing sunscreen*
• *assuming that sunscreen is applied properly
SPF
• Percentage of Protection from damaging UV rays:SPF 15 = 92%SPF 30 = 97%SPF 40 = 97.5%
