Millions of women are damaging their breasts by wearing ill-fitting bras, according to a new study.

Scientists say most bras do not give enough support to prevent irreparable and painful stretching of ligaments during exercise.

Up to 95 per cent of women are thought to be at risk - mostly because they are ignorant or embarrassed about their true bra size, researchers say.

The findings come from treadmill tests carried out on 100 women by Portsmouth University sports scientist Dr Joanna Scurr.

Wendy Hedger, researcher, is pictured with a model testing a sports bra

She found that breasts typically move up to 21 cm - or eight inches - and jiggle around in every direction while a women is running. However, most bras are designed to limit just vertical movement.

Dr Scurr - who has tested 50 bra designs on hundreds of women over the last three years -  believes the speed at which breasts move could be the key to preventing breast pain and damage to fragile ligaments.

Her team has helped design a new, extra supportive bra made with moulded plastic which goes on sale later this year.

"Of the women I have seen during my work I would say only five per cent were wearing the right size bra," said Dr Scurr.

"Most women wear an underband that is too large and a cup size that is too small. Wearing the wrong size bra can cause discomfort and offers reduced levels of support that can lead to stretching and ultimately sagging."

Women experience the most discomfort when their breasts accelerate or decelerate, the scientists found.

Poor bra design is partly responsible.

Ground breaking new research shows that women could be damaging their breasts because they are wearing the wrong bras

Wendy Hedger, a researcher on Dr Scurr's team, said: "Some women cause breast pain or discomfort by not buying the right sized bra.

"There's a social stigma about certain sizes. For instance many women don't want to be seen as too small or too big and buy a bra that doesn't fit well in order to be what they consider to be a 'normal' size.

"Many other women are unaware they are wearing a badly fitting bra or unknowingly wear the wrong bra size because they are routinely being sold ill-fitting bras.

"Some women forget their shape and size change over time and they may have to go through several changes in bra size over their lifetime - especially after breastfeeding and the menopause." 

Enlarge 

A graphic that shows the movement breasts make when a woman walks or runs

The Portsmouth breast biomecahanics team  has helped design a new 'high-impact bra' with New Zealand manufacturer QP Sports which will go on sale in Europe this summer.

The bra has solid cups that are designed to protect the breasts when playing contact sports such as football and rugby.  

Miss Hedger said: "They came to us because they knew their bra protected women in high-impact sports but they weren't sure it supported women well enough. The tests included measuring precisely how much breasts moved in all three directions, as well as more subjective tests about how women felt about the fit, the shape, the strap design and the underband and so on."

Last year, a British Medical Association conference called for free bra fittings to be offered on the Health Service to cut the number of unnecessary breast reductions.

It is thought women tend to overestimate the width of their back, while undestimating their cup size.

Chaffing from material and wires can also cause discomfort.