More than 80 per cent of women are wearing the wrong size bra.
The size of our boobs can change for a number of reasons, including if we lose or gain any weight, but lots of us are guilty of getting measured and sticking to that size for years.
So how do you know if you're wearing the right bra? And how often should you buy a new one?
Bra fit expert and technical manager Julia Mercer answers these important questions.
How do I know if I'm wearing the right bra?
There are a few tell-tale signs that you're not wearing the right size bra.
This is when it looks like your boob is coming out under the cup. It's caused when the under-band is too big and the cup is too small.
Julia says: "A good fitting under-band should fit firmly but not too tight.
"The best way to check that a bra is fitting correctly is to lift the arms up and twist the body, the bra shouldn't move but stay in place at all times."
This is when the boobs spill out of the side. It's caused by the cup being too small. It can be very painful.
To check the cup fits correctly, make sure it is fully encasing ALL the breast tissue.
You should adjust your straps so you can just fit two fingers on top of each other underneath.
A good way to check if your bra is giving you enough support is to slide the straps off and see if the cups are still supportive.
The straps are designed to hold the cups up, not to give support.
Julia says: "Some larger breasted ladies may suffer with sore red marks on their shoulders where the straps have been over adjusted with the intention of gaining extra support.
"If straps are shortened too much the breast will fall forward and the back of the bra will work its way up, therefore not giving support at all."
The four-boob effect
This is when the incorrect cup size pushes the tissue up. It can look very unflattering when you're wearing clothes.
Julia says: "This is a common problem we see regularly.
"It's very common with women who have put on weight as the breast is made up of 75% fat.
"Some women don't want to go up a cup size and continue to wear the wrong size which can make outwear look unflattering.
"Did you know that if you wear the correct cup size you can actually look smaller?"
According to Julia: "Unfortunately every woman, no matter their size, has this issue and can be made worse if the under-band of the bra is too tight.
"A good tip is to wear a shaped back bra as this smoothes any lumps and bumps."
Cups are too big
If you've lost weight recently, there is a good chance you cups will be too big.
This means they won't support the breast tissue properly, and it can also make your bra look unflattering.
The cup and the under-band should fit snugly.
How are bras measured?
Bras are fitted by taking two measurements, and it only takes a few minutes.
You can wear your old bra while these measurements are being taken.
The band size is the size of your rib cage, and is taken by measuring just below the strap of your existing bra.
It's recorded in even numbers, e.g. 30, 32, 34, 36.
The second measurement is the bust.
The person doing your fitting will then work out the difference between the rib cage and the bust size and work out your cup size. This will be a letter, e.g. A, B, C, D, DD.
How long do bras last?
If we're being honest, most of us have bras in the drawer which have seen better days.
They're not quite white anymore and they're definitely no longer sexy - but they're just so comfy.
But it looks like we should be replacing them more often than we thought.
Julia says: "In my opinion, a bra is at its best in its first year of being worn".
How often should I wash my bra?
This is something that causes of a lot of debate between women.
Some will wash their bra every time they wear it, as they would with knickers, while others will wear it a number of times before popping in the laundry basket.
Julia says: "I would recommend washing after each use as this keeps your bra clean and fresh."
What can I do with my old bras?
Of course you can just pop them in the bin, but lot of shops offer a great recycling service.
How do I pick the right sports bra?
When it comes to buying a sports bra, lots of women find themselves a bit lost.
Luckily, Julia has a few tips for finding the right one for your shape.
She says: "A good fitting sports bra can reduce the amount of bounce and provide extra confidence, in turn helping you make the most out of your workout.
"Having the right support for your breasts during exercise is so important and provides the foundation for a great work out.
"Your breasts move in a figure of eight motion when you're running and can move up to 7cm in any direction during exercise so finding an impact level that bests suits your activity is key.”
Tips for bra shopping
Know your body type: Finding which bra shape suits you is just as important as getting the size correct.
Be open minded: Try new sizes if recommended by the sales assistant. Getting used to a new size can feel quite strange to begin with, especially if you have been wearing the wrong size over a long period of time.
Have an idea in your head as to what kind of bra you’re after: Whether that’s a day to day bra, strapless, sports bra or a style for special occasions.