IF your bras have you looking more like Mrs. Doubtfire than Jane Mansfield, it might be because they don’t fit properly.

It’s a widespread problem – eight out of 10 women are unsuspectingly wearing an ill-fitting bra, according to industry estimates. And a study conducted by Wacoal America last year concluded that four out of every 10 women are off in both band size and cup size.

Jo Jefferson, of figleaves.com, says she’s constantly stunned when confronted by women who still haven’t figured out how essential it is to be professionally fit for a bra.

“I was talking to a customer recently who was so unhappy with her body, she was planning to undergo breast augmentation,” Jefferson says.

“We measured her and discovered she had been wearing bras that were three cup sizes too small for her. Once she was fitted correctly, she realized she didn’t need a boob job after all. She’s a good example of how the right bra can transform [a woman’s] silhouette.”

Once you’ve been measured, it’s essential to get an updated fitting every year, says Dawn Kenney, a regional consultant for Wacoal. “There are no shortcuts,” she says.

Additional fittings are vital if a woman has lost or gained a significant amount of weight (anything over 15 pounds), gone through menopause or given birth.

“The more your hormones are acting up, the more your breast tissue is changing size,” she says.

Telltale signs that you’re a victim of an ill-fitting bra include “straps that slip off your shoulders, a band that cuts into your skin leaving impressions or a back strap that rides up,” Kenney says.

Your bra is too small “if it smashes your breasts, causing them to ooze out the top of the bra and around the fabric near your arms,” adds Jefferson. Puckering or wrinkling cup fabric is another giveaway sign, she said.

The clearest signal that women need to work on their bra-purchasing habits comes from a survey carried out by Bali. It reports that 50 percent of us buy a bra without trying it on.