The study found nearly 80 percent of respondents don't know how to wear a bra properly. The study findings revealed most commonly that bras were too tight or too small, or worn too many hours without a change or readjustment.

And that, health officials said, may lead to health problems related to the breast and supporting muscles.

"Local women should attach more importance to proper bra wearing. Long-term improper wearing could affect your health," said Yu Junde, director of the Shanghai Women's Disease Rehabilitation Commission, the group that coordinated the survey.

The women in the survey were between 18 and 50 years old, and were interviewed at company work sites in the city about breast health issues.

Too tight a bra can hurt muscles on the shoulder and back and influence blood circulation, doctors said.

"An uncomfortable bra can lead to different kinds of breast diseases. A woman should not wear a bra longer than 10 hours within one day," said Dr Li Zhuying from Liren Women's Hospital's breast department.

"It is better to have the body remeasured and choose a proper bra every three months."

He said 25 percent of local women between 25 and 45 years old have various breast illness, which may be related to improper use of bra.