The wrong bra size: With around 80 per cent of women believed to be wearing ill-fitting lingerie, we could be inadvertently contributing to sagging breasts, bad posture, back pain or even abrasions and rashes. Several factors including weight loss or gain, medication, contraceptive pills, the menstrual cycle, pregnancy and menopause can affect breast size. It's important to buy new bras every year to make sure you have the correct size. Get an in-store fitter to measure you. And don't forget to wear a sports bra when you exercise.