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Avobenzone

The meaning of «avobenzone»

Avobenzone (trade names Parsol 1789, Milestab 1789, Eusolex 9020, Escalol 517, Neo Heliopan 357 and others, INCI Butyl Methoxydibenzoylmethane) is an oil-soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays.

Avobenzone was patented in 1973 and was approved in the EU in 1978. It was approved by the FDA in 1988. Its use is approved worldwide.

Pure avobenzone is a whitish to yellowish crystalline powder with a weak odor,[1] dissolving in isopropanol, dimethyl sulfoxide, decyl oleate, capric acid/caprylic, triglycerides and other oils. It is not soluble in water.

Avobenzone is a dibenzoylmethane derivative. Avobenzone exists in the ground state as a mixture of the enol and keto forms, favoring the chelated enol.[2] This enol form is stabilized by intramolecular hydrogen-bonding within the β-diketone.[3] Its ability to absorb ultraviolet light over a wider range of wavelengths than many other sunscreen agents has led to its use in many commercial preparations marketed as "broad spectrum" sunscreens. Avobenzone has an absorption maximum of 357 nm.[4]

It is subject to keto-enol tautomerism and exists predominantly enol when dissolved. Upon UV radiation, it may convert to keto form, while converting back to enol form after placing in dark.[5]

Avobenzone is sensitive to the properties of the solvent, being relatively stable in polar protic solvents and unstable in nonpolar environments. Also, when it is irradiated with UVA light, it generates a triplet excited state in the keto form which can either cause the avobenzone to degrade or it can transfer energy to biological targets and cause deleterious effects.[2]

Avobenzone has been shown to degrade significantly in light, resulting in less protection over time.[6][7][8] The UV-A light in a day of sunlight in a temperate climate is sufficient to break down most of the compound. Data presented to the Food and Drug Administration by the Cosmetic, Toiletry and Fragrance Association indicates a −36% change in avobenzone's UV absorbance following one hour of exposure to sunlight.[9] This degradation can be reduced by using a photostabilizer, like octocrylene. Other photostabilizers include:

Complexing avobenzone with cyclodextrins may also increase its photostability.[17] Formulations of avobenzone with hydroxypropyl-beta-cyclodextrin have shown significant reduction in photo-induced degradation, as well as increased transdermal penetration of the UV absorber.[18]

According to some studies, "the most effective sunscreens contain avobenzone and titanium dioxide."[19][20] Avobenzone can degrade faster in light in combination with mineral UV absorbers like zinc oxide and titanium dioxide, though with the right coating of the mineral particles this reaction can be reduced.[21] A manganese doped titanium dioxide may be better than undoped titanium dioxide to improve avobenzone's stability.[22]

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