Sunscreen Photostability

Source: graur codrin | Freedigitalphotos.net

As you may have already read in this post, a good sunscreen requires protection for both UVA and UVB. Yet, even if the formulation offers protection against the harmful rays doesn't mean it's 100% reliable. Another step that manufacturers need to look at to ensure sun protection is photostability of their sunscreen ingredients. To be photostable means that the sunscreen UV filters must remain stable under sun exposure. Some sunscreen ingredients break down immediately under sunlight, rendering their protective capabilities as useless. An interaction between different ingredients needs to be carefully analyzed.

Take note that the question of photostability lies only on chemical sunscreens as physical sunscreens are highly photostable. So if you're using a physical sunscreen, there is no need to worry about photostability. On the other hand, not all chemical UV filters can remain stable under the sun. UV filters such as avobenzone and octinoxate are highly unstable UV filters, but if they are combined with other more stable ingredients, then the problem of stability is solved.

For the layperson, studying about the interaction among ingredients can appear very complicated. Several online resources are available to guide consumers about sunscreen photostability. But, to make matters more simple, Skin Cancer Foundation offers a Seal of Recommendation for sunscreens that have met their photostability criterion. Keep in mind though that it doesn't mean that products without the Seal are automatically unstable; perhaps some of these just haven't undergone the foundation's testing yet.

Among the suncreen products that are found to be photostable are Hawaiian Tropic, Alba Botanica, Aveeno, Cetaphil, Obagi, Jergens, Copperstone, Physician's Formula, Serious Skin Care, Avon, Banana Boat, and Shiseido. For a complete list of brands bearing the Seal of Recommendation, see this page.

Meanwhile, if you are highly interested on the mechanisms of sunscreens, here are some recommended readings to help you get started:

Skinacea: Sunscreen Stability

Skin Cancer Foundation: Does Sunscreen Become Ineffective with Age?

Hallstar: Sunscreen Photostability 101

FDA: Photostability

To know more about sun protection, read my article: The Sun and Your Skin