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Question: How can I tell if my sunscreen is stable?

Answer:

Your sunscreen is photostable when the UV filters in it don’t break down once exposed to sunlight. If this does happen, the sunscreen becomes ineffective and doesn’t protect you as well against UV rays.

Photostability is only an issue if your sunscreen contains avobenzone (Check here for its other names) If your sunscreen doesn't have avobenzone as one of its active ingredients, then you're good. Most other UV filters are photostable, so you don't have to worry about photostability issues with non-avobenzone sunscreen filters.

If your sunscreen does contain avobenzone, check to see if there is octinoxate. Avobenzone is already unstable, but can become even more unstable when combined with octinoxate. Avobenzone, however, can be stabilized with octocrylene or other UV filters (wow, what a mouthful!).

Basically, here's what you should do to check photostability:

Step 1:

Does your sunscreen have avobenzone? If not, then you're good. Your sunscreen is probably photostable. If it does, then move onto the next step.

 

Step 2:

So your sunscreen has avobenzone. Chances are, it will not be the only active ingredient in your sunscreen (due to avobenzone being highly unstable). Check to see if one of the other UV filters is octinoxate.

 

Step 3:

If octinoxate is the only other active besides avobenzone, your sunscreen is not stable. If there is avobenzone + octinoxate + octocrylene, then your sunscreen is still photostable because as long as avobenzone is stabilized by octocrylene, avobenzone will remain stable (even in the presence of octinoxate).

 

Step 4:

If your sunscreen has avobenzone, octinoxate, and some other UV filter besides octocrylene, then your sunscreen may be photostable, but to what extent is unknown. Other UV filters (besides octocrylene) can stabilize avobenzone as well, but it seems like octocrylene is one of the better known stabilizers.

Hopefully the above isn't as confusing as it sounds! Choosing a sunscreen really is a daunting task because after you've found one that is photostable, you then have to find one that has a good finish, doesn't break you out, offers enough protection, etc. All I have to say it, GOOD LUCK! =)

For more information about how to choose a good sunscreen, sunscreen recommendations, and other information, check here.

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