One of two molecules this week
July 16, 2018
In a few years, coral in Hawaiian waters will no longer have to put up with us.
What molecules are we?
Image of Oxybenzone 3D Image of Oxybenzone
Figure 1: Oxybenzone
Image of Oxybenzone 3D Image of Oxybenzone
Figure 2: Octinoxate

Oxybenzone (Figure 1), formally 2-hydroxy-4-methoxybenzophenone, is an old-line sunscreen ingredient developed in the 1950s by the now-defunct General Aniline & Film (GAF) Corp. It is marketed today under several tradenames. The compound was first synthesized in 1906 in Germany by chemists B. König and Stanisław Kostanecki.

The US Food and Drug Administration approved the use of oxybenzone in sunscreen products in the 1980s. In 2013, a revised approval allowed concentrations of up to 6%. Oxybenzone absorbs light in the UV-B (280–315 nm) and short-wavelength UV-A (315–355 nm) ranges.

Octinoxate, or octyl methoxycinnamate (Figure 2), is a more recent sunscreen component. It is marketed by Merck under the tradename Eusolex 2292 and by BASF as Uvinul MC80. It absorbs primarily in the UV-B range.

Both compounds are widely used in sunscreens, but this past May, the Hawaii legislature passed a bill that outlaws products that contain them, effective January 2021. The bill is based on studies that show that oxybenzone may harm coral larvae and that both compounds may “bleach” coral, causing it to lose symbiotic algae.

Sunscreen makers, of course, deny that the studies are valid. Nevertheless, Hawaii governor David Ige signed the bill into law earlier this month.

Oxybenzone hazard information

GHS classification*: skin irritation, category 2
H315—Causes skin irritationChemical Safety Warning
GHS classification: serious eye irritation, category 2A
H319—Causes serious eye irritationChemical Safety Warning
GHS classification: specific target organ toxicity, single exposure; respiratory tract irritation, category 3
H335—May cause respiratory irritationChemical Safety Warning

*Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.

Octinoxate hazard information

GHS classification: not a hazardous substance

MOTW update

Fluralaner was the Molecule of the Week for March 26, 2018. It is a popular flea medication for dogs that needs to be administered at only 12-week intervals. Now, fluralaner and its cousin flea protectant afoxolaner might be used as an oral medication to kill disease-spreading mosquitoes when they bite treated people. A modeling study by researchers at TropIQ Health Sciences (Nijmegen, The Netherlands) and California Institute for Biomedical Research (La Jolla) found that in areas at risk, giving people these drugs would substantially reduce incidences of malaria and Zika. The drugs kill carrier mosquitoes via an attack on an insect-specific ion channel.

Oxybenzone fast facts

CAS Reg. No.131-57-7
Molar mass228.24 g/mol
Empirical formulaC14H12O3
AppearanceWhite to pale yellow crystals or powder
Melting point65.5 ºC
Boiling point150–160 ºC (5 torr)
Water solubility13 mg/L

Octinoxate fast facts

CAS Reg. No.5466-77-3
Molar mass290.40 g/mol
Empirical formulaC18H26O3
AppearanceColorless to pale yellow viscous liquid
Boiling point198–200 ºC (3 torr)
Water solubility<1 mg/L

MOTW update:
May 20, 2022

Oxybenzone is a long-time sunscreen ingredient that in recent years was found to damage coral reefs. Beginning in 2021, sunscreens containing oxybenzone were outlawed in Hawaii.

William A. Mitch and colleagues at Stanford University (CA) have now discovered how oxybenzone damages coral. When coral metabolizes the compound, it converts its hydroxyl group to a glucoside. In contrast to the sunblocker oxybenzone, the metabolite is a phototoxin; when it absorbs sunlight, it forms reactive oxygen species that corrode coral tissue. 

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