A scientific study says stress in humans continues to worsen despite the body's immunity to outside stimuli or change.

Led by professor Kim Kyong-tai, a research team at Pohang University of Science and Technology said Monday that it solved the mechanism of the stress hormone catecholamine that increases secretion from repeated stimulation.

Experiments showed accumulated stimulation on endocrine cells increased the amount of vesicles inside the cells, which in turn raised the secretion of the stress hormone.

The team said stress is caused by the stress hormone catecholamine inside blood and continuous stimulation raises the stress level instead of lowering or maintaining it.

The finding is the cover story of the March issue of the U.S. medical journal Endocrinology.