Final answer:
Sunblocks use inorganic compounds like zinc oxide to reflect UV rays, while sunscreens use organic compounds to absorb them. An SPF of 30 is recommended for filtering out 97% of UVB radiation. Broad spectrum products protect against UVA and UVB, and should be reapplied every two hours.
Step-by-step explanation:
The Chemistry of Sunscreens and Sunblocks
Sunscreens and sunblocks play a vital role in protecting our skin from the harmful effects of ultraviolet (UV) radiation. Sunblocks, which contain inorganic ingredients like zinc oxide or titanium dioxide, primarily protect by reflecting and scattering UV rays. Their texture can be grainy, and they are sometimes difficult to spread evenly due to the inorganic components used.
On the other hand, sunscreens typically consist of organic compounds such as oxybenzone, avobenzone, homosalate, and octinoxate that absorb UV radiation and convert it into heat, which is then released from the skin. Sunscreens are known for their smoother application compared to sunblocks. Many manufacturers combine ingredients from both sunscreens and sunblocks to provide comprehensive protection against solar energy.
The Sun Protection Factor (SPF) is a measure of how well a sunscreen can protect skin from UVB rays. An SPF of 30 is recommended to filter out 97% of UVB radiation, providing adequate protection for most individuals. It's also important to select products labeled as broad spectrum for UVA protection. To maintain effectiveness, sun protection should be reapplied every two hours, especially after swimming or sweating, as no products are completely waterproof.
While sunscreen helps in preventing sunburn and skin cancer, UVB radiation is also necessary for the production of vitamin D. To balance sun protection with vitamin D synthesis, the American Academy of Dermatology suggests obtaining vitamin D through foods or nutritional supplements instead of excessive sun exposure.