Why Does an Onion Make the Tears Come?
That is nature’s way of protecting the eyes from the smarting which the onion would cause in your eyes if the tears did not come quickly and overcome the bad effect so produced. Tears are provided for washing the ball of your eyes. Every time you wink a little tear is released from under the eyelid, and the wink spreads it all over the eyeball. This washes down the front of the eyeball and cleanses it of all dust and other things that fly at the eye from the air. Then the tear runs along a little channel, much like a trough, at the lower part of the eye, and out through a little hole in the eye, and in this case the tear is really only an eye-wash. Many things, but more often sadness or injured feelings, start the tears coming so fast from under the eyelid that the little trough at the bottom and the hole in the corner of the eye are too small to hold them or carry them off, so they roll over the edge of the lower eyelid and down the face. These are what we call tears. Among other things that will cause tear-glands to cause an over-supply of eye-wash to come down, are onions. What they give off is very trying to the eyes, and so, just as soon as the something which an onion throws off hits the eyeball, the nerves of the eye telegraph the brain to turn on the tears quickly, and they come in a little deluge and counteract the bad effect of the onion.