While British Columbian women spend millions of dollars on bras, experts say up to 90 percent of them are still wearing the wrong size.

The badly-fitting lingerie is not only causing cosmetic concerns, like cups running over and prematurely sagging breasts, it also contributes to serious health issues like posture problems and headaches.

"You can go to a chiropractor on a Monday morning and by Friday if you're not wearing a good bra and your breasts and pulling, pulling, pulling down -- your shoulders are out," Diane Thompson of Diane's Lingerie told CTV News from her South Granville store.

A bad bra accentuates back fat, and overly tight straps can cause painful grooves. Thompson says often the back band is usually too big, too tight or worn out altogether and the cups are often overflowing.

So does a professionally fitted bra really make that much difference?

Our volunteer models agreed to pose for before and after shots, and universally agreed they felt younger, slimmer, taller and more comfortable in better fitting undergarments.

'Now I realize the first thing I do in the morning is put on a good bra and the last thing I do is take it off," said bra fitting customer Jennifer Ricci.

And while the women represent a cross-section of ages and sizes, Thompson says anyone at any age can benefit from a good bra. Her oldest customer came in for her 100th birthday and left delighted.

"Once they get in a proper fitting bra, they can stand properly, their shoulders back and we hear it all the time in the fitting room, ‘you have just changed my life,'" she said.

Your bra size changes several times throughout your life because of weight and hormone fluctuations, pregnancy, menopause, and even the birth control pill.

Thompson recommends getting fitting for a new bra at least twice a year.

Women who have had mastectomies, lumpectomies or breast reconstruction have some unique physical and emotional challenges during breast fittings.

Many professional bra fitters like Thompson are specially trained in after-surgery care and certified in prosthetic fittings.

Related: Diane's Lingerie website

With a report from CTV British Columbia's Lynda Steele