A new study has found that cutting onions slowly using sharp knives can reduce eye irritation.

Tears from the eyes when cutting onions are caused by a chemical reaction in the eyes. When onions are cut, a volatile compound – syn-Propanethial-S-oxide – is released into the air and affects the eyes.

The new study, published in the journal PNAS, examined the factors that cause this compound to be released as an aerosol in varying amounts during onion cutting.

In the study, scientists cut onions using a special type of gluten (which could be fitted with different types of blades). At the same time, they covered the onion pieces with paint to better observe this process.

In each trial, the scientists varied the size, sharpness and cutting speed of the knife and used a microscope to measure before and after use.

In the study, researchers found that the amount of material released was directly related to the sharpness of the knife and the speed at which the onion was cut.