I work with raw onions on a daily basis, and I was wondering if someone could tell me why slicing and pealing them hurts my eyes soo much.
Also, is there anything I can do to prevent this (besides avoiding the onions), and can prolonged exposure have lasting effects...or maybe even cause damage?
Answered by Richard E. Gans, M. D. (xx102@ofcn.org)
Onions contain a compound called propanethial-S-oxide which is a sulfur-containing substance. This compound was first discovered in 1985 by researchers at the University of St. Louis. They found that when this substance comes in contact with water, part of it is converted into sulfuric acid. It is this dilute quantity of sulfuric acid that causes your eyes to tear. The substance is liberated when you cut the onion and when it comes in contact with the tearfilm on the front surface of the eye, it turns into sulfuric acid, which burns and irritates your eye and causes a reflex to occur which creates more tears.
This small amount of sulfuric acid is irritating, but it is not enough to cause any damage to the eye.
I am told that if you chill the onion for one hour in the refrigerator before slicing it or if you soak it in water so that the acid is diluted before slicing it, your eye irritation will be lessened.
PLEASE NOTE: The information contained on this system is not intended to supplant individual professional consultation, but is offered as a community education service. Advice on individual problems should be obtained directly from a professional.
Copyright, 1994. Richard E. Gans, M.D.
Last Modified: August 23, 1996