17B. UV Protection
UVA effects on skin
causes photoaging and persistent pigment darkening
UVB effects on skin
causes tanning and sunburns, and can cause skin cancer due to an accumulation of damage over year
UVA & UVB effects on skin
can thicken the epidermis, weaken the dermis, cause immunosuppression, and increase the production of reactive oxygen species (ROS)
What is important in sunscreen
it is important to have broad coverage across the full spectrum of UV light, in order to provide the most protection possible.
How to Apply Sunscreen
should be applied 20 minutes before going outside, giving it time to be absorbed into the skin and work effectively - A proper dose of sunscreen is 2 mg/cm2 , roughly corresponding to 1 tsp each for the head, face and each arm, and 2 tsp each for each leg and the trunk. -Sunscreen should be reapplied every two hours and after coming out of the water. *important to use the highest SPF possible, in order to get the best possible protection given true sunscreen usage patterns
The pathway that produces damage to skin
sun → UV light → skin → UV interaction with skin components → damage → pathology
effects of UV light from sun
-acute changes, including a worsening of porphyrea cutanea tarda, photophytodermatitis, polymorphous light eruption, and melanoma -chronic changes, such as solar lentigos, idiopathic guttate hypomelanosis, and poikiloderma of Civatte
Antioxidants
-buildup of ROS molecules in the skin is thought to be an important contributor to the development of the negative effects of UV light on the skin -these work by scavenging ROS molecules, binding them up before they can strip electrons away from the molecules in the skin and cause damage -Chemicals such as vitamin E, glutathione, fern leaf extract (polypodium leocotomos), polyphenols (as found in honey, red wine, green tea, and chocolate) and catalase have been shown to have antioxidant effects.
New rules affecting the way sunscreens are labeled
-highest SPF will now be limited to "50+". -The words "broad spectrum," if used, will now mean that the sunscreen provides both UVA and UVB protection. no longer be any "waterproof" sunscreens the words "water resistant" will be used instead, and will be presented with a recommended time for reapplication. The word "sunblock" is also being phased out in favor of the word "sunscreen," to better capture the true role of UV protection.
Sunscreens
-prevent UV light from reaching the skin -types: -->Physical Blocker -->Chemical Blocker
SPF as a measure of how long the UV protection will last for
SPF is NOT a measure of how long the UV protection will last for. Rather, it only measures how much of the UV light it will allow through. A sunscreen of SPF 10 and one of SPF 50 will last for the same amount of time on the skin, but the SPF 50 will provide much better coverage and protection while it is applied.
Ways to prevent negative effects of UV exposure
Sunscreens Antioxidants
Chemical Blocker Sunscreen
These are chemicals that absorb the energy of the incident UV light, preventing it from reaching the layers of the skin and causing damage.
Physical Blocker Sunscreen
These are chemicals that physically block the UV light by reflecting the light away from the skin. These sunscreens will typically contain either Titanium Dioxide or Zinc Oxide.
SPF: Sun Protection Factor
number between 5 and 70 -fraction of light that the sunscreen will allow through when applied correctly For example, a sunscreen of SPF 30 will allow 1/30th of the incident UV light to reach the skin. This means that a person wearing an SPF 30 sunscreen can stay in the sun for 30 times longer than a person who wears no sunscreen, and they will receive the same amount of UV exposure, provided that the proper amount of sunscreen has been applied and maintained across the duration of sun exposure **SPF applies only to UVB light (UVA protection is not included in this number)
