Dr. Norman Levine: My understanding is that inorganic sunscreens tend to be less substantive, and they actually break down in the sun. Is that an issue with these kinds of products?
Dr. Darrell S. Rigel: Actually, sunblocks and sunscreens both break down. The sunscreens or the organic ones are catalysts effectively; so they will go on and on and continue to break down until at some point they are broken down themselves. So typically in about two hours, most of the sunscreens — the organic sunscreens — are broken down. How long they last is called substantivity.
With the sunblocks, what will happen is that they will clump on the skin over time. So instead of having a nice uniform spread, you begin to see the areas where the sun can just get through.
Dr. Norman Levine: Is the vehicle into which the sunscreen or sunblock is incorporated an important issue? When I see people spraying the sunscreen on their kids because the kids like the sprays, it seems intuitively that they are not getting the same degree of protection. What are your thoughts?
Dr. Darrell S. Rigel: The vehicle does make a difference. I look at it differently. I want people to use what they like the best, because if they don’t like it, they are not going to use it. So, if you have a gooey, yucky vehicle, it could be the best sunscreen in the world, but nobody would use it. Each of the vehicles has advantages and disadvantages. The gels tend to wash off a little easier than something heavier. Believe it or not, sprays are now the number one formulation sold in the United States.
One note about the spray is that it is very important to spray on two coats, because with the spray, you often do not know where you have missed. With the cream, you typically know where you apply it in most cases. So what is really important is making sure that people do cover themselves uniformly.