A graduate student has discovered that an excessive amount of a human defense mechanism against numerous microbes can cause intestinal problems.

Ha Eun-mi of Ewha Woman's University in a paper presented Friday said the enzyme Duox produces in the body reactive oxygen species (ROS), an anti-germ compound which stops the excessive multiplication of microbes and germs.

Though the ROS compound can curb microbe growth, she said too much of it can cause intestinal inflammation called enteritis, which is incurable and potentially life-threatening if unchecked.

Her research is featured in the latest edition of the American journal Science.