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Wed Jul 07, 2004 7:55 pm  |
Has anyone here heard of sunscreens using Avobenzone or Parsol 1789 or similar chemical ingredients as the UV protection being unstable? I've read reams of it on other sites. They say that these ingredients need to have a stabilizer such as octocrylene or else they are "unstable", meaning, I guess, that they don't provide the SPF claimed on the label. They also suggest that even if it has octocrylene, if it also has octinoxate, then the two ingredients effectively cancel each other out.
My thought is, if all this is true, then many of the sunscreens recommended by dermatologists and on our drugstore shelves would have been removed due to public outcry.
Any thoughts on all this stuff? |
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Thu Jul 08, 2004 11:32 am |
| Well, unstable means they break down in the presence of UV radiation. So, the long and short of it is that you must reapply. Many of the chemical sunscreen ingredients can only absorb so much UV radiation before they become inactive...thus the "reapply every two hours etc." rap. As for the ones that claim six hours waterproof, etc. They may stick to your skin for six hours but that doesn't necessarily mean you are getting the full spf protection over all that time period. It's very aggravating. Until we get a better system for handling spf's and sunscreen ingredients etc., I try to avoid long periods of sun exposure and use hats, physical screens (like long sleeved shirts, etc.) and reapply like crazy. |
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Thu Jul 08, 2004 12:10 pm |
this forum has a really informative thread about this...
http://forums.handbag.com/showthread.php?s=&threadid=151113
chlipaddi will also answer pm's about this, but you do need to be a registered user for this |
_________________
my new jewellery website:www.gentle-medusa.com |
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marmalade
New Member
 
Joined: 13 Jun 2004
Posts: 7
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Thu Jul 08, 2004 8:39 pm |
Hi ~
The American Academy of Dermatology recommends reapplying sunscreens every 1.5 hours, because most of the older chemical sunscreen filters (avobenzone included, although it can be stabilized by some ingredients, to varying degrees) do break down with exposure to light - there's a fair bit of scientific literature discussing this, hence the suggestion. As betterat40 indicates, photounstability isn't an inability to reach the advertised spf originally (the FDA tests for this), but the loss of the sunscreen's efficacy over time/light exposure. Physical filters like zinc oxide and titanium dioxide generally are not prone to this photodegradation, and are pretty stable; also newer filters like the mexoryls [recently covered on ABC news and such], tinosorbs, uvinul As, etc, that aren't yet on the market in the US  |
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Thu Jul 08, 2004 9:04 pm |
Thanks for all your responses. I've read the link that was here and it's great.
I guess what I don't get is, when it comes to sunscreen for the face, most of us just apply it in the morning and do not re-apply throughout the day, as that would require removing makeup etc. So then, many of the sunscreens we see here contain avobenzone without stabilizers, so they really aren't appropriate for city-life / daily care.
I know the recommendations for most sunscreens say to re-apply every 2 hours, but since many of us don't, there really should be more said about this.
Oh well!  |
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