Research Pathways to Photostable Sunscreens

Feb 1, 2008 | Contact Author | By: Craig Bonda, The HallStar Company
Your message has been sent.
(click to close)
Contact the Author
Save
This item has been saved to your library.
View My Library
(click to close)
Save to My Library
Title: Research Pathways to Photostable Sunscreens
sunscreenx photostabilityx UV filtersx triplet/singlet quenchingx fluorescencex
  • Article
  • Media
  • Keywords/Abstract

Keywords: sunscreen | photostability | UV filters | triplet/singlet quenching | fluorescence

Abstract: This article provides a visual depiction of pathways that UV filters undergo when exposed to solar radiation; such pathways often lead to photo-instability. A fluorescence technique is described that has led the author to identify compounds that preserve photostability in a novel manner­— by quenching the UV filter’s singlet excited state.

Excerpt Only This is a shortened version or summary of the article you requested. To view the complete article, please log in or create an account. Registration is Free!

On Aug. 27, 2007, the US Food and Drug Administration (FDA) published its long-awaited proposal to amend regulations governing sunscreens sold in the United States.1 In it, the FDA proposed new standards for formulating, testing and labeling OTC sunscreen drug products with UVA and UVB protection. For the first time, the FDA addressed the issue of sunscreen photostability and its importance to sunscreen performance:

“The FDA agrees that it is important to address the photostability for sunscreen drug product formulations. Unstable product formulations present the problem of degradation of product effectiveness during actual use,” the agency stated, adding, “The FDA is proposing to address photostability by adding a pre-irradiation step to the in vitro test method for measuring UVA protection. …" With this pronouncement, the FDA put sunscreen marketers and formulators on notice that photostability is the foundation upon which future sunscreen products must be built.

So what is photostability and how does one lay a photostable foundation? What causes a sunscreen to lose photostability, and what, if anything, can a formulator do about it? Finding the answers to those questions has been the focus of research at HallStar for more than 10 years. The answers begin with some general background on the photophysics and photochemistry of UV filters.

Excerpt Only This is a shortened version or summary of the article you requested. To view the complete article, please log in or create an account. Registration is Free!

 

Close

Excited States

 Excited States

Figure 1. A graphical depiction of the Deactivation of Excited States

 Figure 1. A graphical depiction of the Deactivation of Excited States

Figure 2. The structures of commonly used photostabilizers

 Figure 2. The structures of commonly used photostabilizers

Figure 3. The idea behind triplet quenchers

 Figure 3. The idea behind triplet quenchers 

Figure 4. Singlet quenching (SQ) drains the singlet

 Figure 4. Singlet quenching (SQ) drains the singlet 

Figure 5. For each donor-acceptor pair

 Figure 5. For each donor-acceptor pair

Figure 6. The visible fluorescence

 Figure 6. The visible fluorescence 

Figure 7. Fluorescence quenching experiments

 Figure 7. Fluorescence quenching experiments

Figure 8. Fluorescent UV filters

 Figure 8. Fluorescent UV filters

Figure 9. Two matched avobenzone sunscreen formulations

 Figure 9. Two matched avobenzone sunscreen formulations

Figure 10. A possible photo-induced reaction scheme

 Figure 10. A possible photo-induced reaction scheme

Figure 11. The photostability of a sunscreen containing both octinoxate (OMC) and avobenzone

Figure 11. The photostability of a sunscreen containing both octinoxate (OMC) and avobenzone

Figure 12. Adding a good amount of octocrylene

 Figure 12. Adding a good amount of octocrylene

Figure 13. Ethylhexyl methoxycrylene quenches the singlet

 Figure 13. Ethylhexyl methoxycrylene quenches the singlet

Bonda Research Pathways

 a DEXSTER is a copyright owned by Hallstar, Chicago, USA.

b At higher chromophore concentrations the relationship between absorption and chromophore concentration becomes nonlinear. This is attributed to a shadow effect, whereby one molecule in a photon’s path casts a shadow on another molecule directly behind it. This leads to underestimation of chromophore concentration, but does not in itself alter the fate of a chromophore after excitation takes place.

Next image >

 
 

Close

It's Free...

Register or Log in to get full access to this content

Registration includes:

  • Access to all premium content
  • One click ingredient sample requests
  • Save articles in the My Library tool

Create an Account or Log In