Dr. Norman Levine: Would you discuss some of the pluses and minuses of the so-called sunblocks versus sunscreens?
Dr. Darrell S. Rigel: The terms sunblock and sunscreen are rather passé now. They are now called organic and inorganic sunscreens. What we now view as organic sunscreens would be the so-called sunscreens from the past. Basically these are agents that primarily absorb the ultraviolet radiation and convert it to a different type of radiation.
Most sunscreens absorb the UV radiation and convert it to a red light wavelength. You do not see that because you’re outdoors and it is bright, but it actually converts it into a little bit of red light, which is not harmful. The so-called sunblocks, like zinc oxide or titanium dioxide, are basically reflectants. So they are just reflecting the waves off the surface but not really changing the energy itself. They both have advantages and disadvantages.
The sunscreen, or what we now call the organic sunscreen, basically absorbs the energy. Additionally, the elements themselves are absorbed into the skin a little bit, which is a bit of concern. There is some absorption of chemicals. If you look at oxybenzone, in fact, it entails a little bit of systemic absorption; however by mixing these chemicals, you can get a much broader and better protection because each of these sunscreen agents have slightly different absorption characteristics.
The inorganic sunscreens, or so-called sunblocks, basically have the same amount of protection across the entire spectrum because they are just reflecting, but you cannot get them to the level of protection that you get with the organic agents.
Although they supposedly are not absorbed, there was one study conducted in Australia, where they applied zinc oxide on the forearm daily for six consecutive weeks and then did a punch biopsy. It turns out you could find micronized zinc in the dermis even after that six weeks of application. Nobody knows if that is good or bad, but it does occur. The best sunscreen has a combination of the two, because then you get the pluses of each one. You get the reflectance as well as the higher intensity in broader spectrum. They are synergistic when you have that mix.