SPF, also known as Sun Protection Factor, measures how well a sunscreen can protect against skin damage from UV radiation. Sunscreens are made up of various organic and inorganic compounds. These compounds are able to absorb UV radiation and release its energy in the form of heat.
Most sunscreens indicate a SPF value. This value represents the ratio of the amount of UV radiation required to cause erythema (redness of the skin) on sunscreen protected skin to the amount of UV radiation required to cause erythema without the sunscreen.
For example, if it normally takes you ten minutes under the sun to develop skin redness, wearing a sunscreen with SPF 15 will allow you to be under the sun for 10 x 15= 150 minutes before developing skin redness. Therefore, sunscreens with higher SPF values tend to be more efficient at protecting the skin from UV damage than sunscreens with low SPF values.
Most sunscreens indicate a SPF value. This value represents the ratio of the amount of UV radiation required to cause erythema (redness of the skin) on sunscreen protected skin to the amount of UV radiation required to cause erythema without the sunscreen.
For example, if it normally takes you ten minutes under the sun to develop skin redness, wearing a sunscreen with SPF 15 will allow you to be under the sun for 10 x 15= 150 minutes before developing skin redness. Therefore, sunscreens with higher SPF values tend to be more efficient at protecting the skin from UV damage than sunscreens with low SPF values.
Reference:
El-Boury, S., Couteau, C., Boulande, L., Paparis, E., & Coiffard, L.J.M (2007). Effect of the combination of organic and inorganic filters on the Sun Protection Factor (SPF) determined by in vivo method. International Journal of Pharmaceutics, 340: 1-5.
Image source:
http://www.skincancer.org/prevention/sun-protection/sunscreen
El-Boury, S., Couteau, C., Boulande, L., Paparis, E., & Coiffard, L.J.M (2007). Effect of the combination of organic and inorganic filters on the Sun Protection Factor (SPF) determined by in vivo method. International Journal of Pharmaceutics, 340: 1-5.
Image source:
http://www.skincancer.org/prevention/sun-protection/sunscreen
