In what ways does sunscreen slow down and prevent sunburns? |

Blocks radiation. Sunblock or sunscreen will interfere with penetration of harmful ultraviolet radiation which has the potential to cause genetic mutations that may lead to skin cancer.
Sunscreen. Sunscreens help prevent sunburn by slowing down the rate of absorbtion of ultraviolet rays by the skin. For example a number 15 sunblocker applied to the skin will cause the skin to absorb only 1/15 of the suns rays as opposed to unprotected skin. In other words, protected skin with sunblocker would take 15 hours to absorb the same amount of radiation absorbed in one hour by unprotected skin.