Tony O’Lenick asks Craig Bonda, an expert in photostabilization and sunscreen technology from Hall Star, "What is the difference between a sunscreen and a photostabilizer?"
A sunscreen is a topical preparation intended to protect its wearer from the harmful effects of UV radiation from the sun. The active ingredients contained in sunscreens are chemical compounds that either reflect and scatter the harmful UV rays, or absorb them and dissipate their energy harmlessly. Throughout the world, government regulations determine which chemical compounds may be used for this purpose, and how they may be used.
The compounds that scatter and reflect the UV rays are metal oxides such as zinc oxide and titanium dioxide. These must be coated to prevent them from engaging in chemical reactions in sunlight that might reduce sunscreen effectiveness. Compounds that absorb and harmlessly dissipate the energy from UV rays are organic, carbon-containing chemicals, often called UV filters. These also have the potential to engage in effectiveness--robbing chemical reactions when exposed to the sun.
Photostabilizers are organic compounds that help to prevent UV filters from losing their effectiveness in sunlight. Some of them help to stabilize UV filter molecules structurally and geometrically through electrostatic and van der Waals interactions, which makes them less likely to take part in chemical reactions. Another type of photostabilizer protects UV filters by helping to dissipate the energy from UV more quickly, thus reducing or even eliminating the possibility of a chemical reaction. This process is called energy transfer, and it can take place when the UV filter and photostabilizer molecules exchange electrons, or even by action at a distance, as a radio transmitter sends a signal to a nearby receiver. In this way, the UV filters are freed up to do their job of protecting the skin by absorbing the harmful rays, while the photostabilizers do the work of disposing of the energy.
Modern sunscreens contain both UV filters and one or more photostabilizers. This makes them much more effective than in the past at protecting the skin both from sunburn and from the aging and other negative effects of UV radiation.