Sunburn; Ouch! The Real Deal on Protecting Yourself!
Solar Ultraviolet (UV) light capable of injuring the skin is classified by wavelength into UVA I (340-400 nm), UVA II (320-340 nm) and UVB (290-320). UVB is responsible for most of the redness of sunburn. UVA is primarily responsible for leading to phototoxicity and long term photo-aging. Sunscreen manufacturers are able to claim broad spectrum protection if their products block at least part of UVA II and UVB.
Avoiding sun exposure between 10 am and 3 pm when UV radiation from the sun is most intense, decreases the risk of sunburn considerably but does not eliminate that risk. Wearing of protective clothing and hats, will prevent sunburn of course to covered areas, but for exposed skin areas Sunscreen/Sunblock lotions should be applied
Sunblock lotions usually contain combinations of organic chemicals which absorb various wavelengths of UV light, most of these primarily absorb UVB-range light. Parsol 1789 (Avobenzone) absorbs both UVA I and UVA II. The compound Menthyl anthranilate and oxybenzone also absorb some UVA II wavelengths. Inorganic physical sunblocks such as Zinc oxide or Titanium dioxide block UVA I and UVA II (these are usually white colored after application but some newer formulations are transparent).
What is the Sun Protection Factor (SPF) and how is it measured?
The Sun Protection Factor (SPF) is calculated by dividing the dose of UV radiation needed to produce minimal redness on the skin protected by sunscreen lotion by that produced by a dose of radiation on unprotected skin. The standard amount of sunscreen is 2mg/cm of skin which means a person wearing a bathing suit needs to apply more than one ounce of sunscreen lotion to cover their unprotected skin areas. Applied in this amount, an SPF of 2 blocks 50 % of the radiation, SPF of 10 blocks 90%, SPF 15 blocks 93% and SPF 30 blocks 97%. The degree of protection from UVA (responsible for photoaging) is hard to measure actually and is less than the protection given by these lotions from the UVB radiation--which causes the sunburn primarily.
Sunscreens should be applied 15-30 minutes before going out into the sun. Most people do not apply a thick enough layer of the lotion to achieve the stated SPF. Studies show that most people only apply apporoximately 1/4 to 1/2 of the recommended amount and this would then give, for example, a stated SPF 15 lotion an actual SPF of 2 or 4. Wind, Heat, humidity, applied insect repellents can all reduce the effect of the sunscreen/sunblock lotion. The American Academy of Dermatology recommends reapplication of the sunscreen lotion every 2 hours, and immediately after swimming or heavy perspiration. Therefore, the important message for using these sunscreen lotions is to apply it on heavily and often, use a broad spectrum sunscreen with an SPF of 15 or above.
Mark L. Siefring M.D. M.S ABIM
Solar Ultraviolet (UV) light capable of injuring the skin is classified by wavelength into UVA I (340-400 nm), UVA II (320-340 nm) and UVB (290-320). UVB is responsible for most of the redness of sunburn. UVA is primarily responsible for leading to phototoxicity and long term photo-aging. Sunscreen manufacturers are able to claim broad spectrum protection if their products block at least part of UVA II and UVB.
Avoiding sun exposure between 10 am and 3 pm when UV radiation from the sun is most intense, decreases the risk of sunburn considerably but does not eliminate that risk. Wearing of protective clothing and hats, will prevent sunburn of course to covered areas, but for exposed skin areas Sunscreen/Sunblock lotions should be applied
Sunblock lotions usually contain combinations of organic chemicals which absorb various wavelengths of UV light, most of these primarily absorb UVB-range light. Parsol 1789 (Avobenzone) absorbs both UVA I and UVA II. The compound Menthyl anthranilate and oxybenzone also absorb some UVA II wavelengths. Inorganic physical sunblocks such as Zinc oxide or Titanium dioxide block UVA I and UVA II (these are usually white colored after application but some newer formulations are transparent).
What is the Sun Protection Factor (SPF) and how is it measured?
The Sun Protection Factor (SPF) is calculated by dividing the dose of UV radiation needed to produce minimal redness on the skin protected by sunscreen lotion by that produced by a dose of radiation on unprotected skin. The standard amount of sunscreen is 2mg/cm of skin which means a person wearing a bathing suit needs to apply more than one ounce of sunscreen lotion to cover their unprotected skin areas. Applied in this amount, an SPF of 2 blocks 50 % of the radiation, SPF of 10 blocks 90%, SPF 15 blocks 93% and SPF 30 blocks 97%. The degree of protection from UVA (responsible for photoaging) is hard to measure actually and is less than the protection given by these lotions from the UVB radiation--which causes the sunburn primarily.
Sunscreens should be applied 15-30 minutes before going out into the sun. Most people do not apply a thick enough layer of the lotion to achieve the stated SPF. Studies show that most people only apply apporoximately 1/4 to 1/2 of the recommended amount and this would then give, for example, a stated SPF 15 lotion an actual SPF of 2 or 4. Wind, Heat, humidity, applied insect repellents can all reduce the effect of the sunscreen/sunblock lotion. The American Academy of Dermatology recommends reapplication of the sunscreen lotion every 2 hours, and immediately after swimming or heavy perspiration. Therefore, the important message for using these sunscreen lotions is to apply it on heavily and often, use a broad spectrum sunscreen with an SPF of 15 or above.
Mark L. Siefring M.D. M.S ABIM