When I first heard the assertion that wearing an underwire bra increases your risk of breast cancer I was quite scared, by then I'd been wearing underwires for longer than I hadn't!!  Fortunately it turns out to be bunk, there's no health risk at all associated with underwires... other than those related to the structural integrity of the bra and whether the wire will poke you if you experience a wardrobe malfunction!!

Here's an article that discusses the topic and another topic close to my heart (snicker), sleeping with a bra on.  I find them comfortable and they are sort of like a security blanket for me, I'm not sure I could sleep topless anymore... I would just feel too... I don't know... unsecured.

http://www.shape.com/lifestyle/mind-and-body/breast-myths-debunked

Underwire bras are definitely not good for breasts that are still growing, even though they don't give you cancer (unless they're, you know, radioactive bras).

I believe they do come in "radioactive"

I read once where natal women who wear there bras to bed have a higher incidence of breast cancer.  That was several years ago.  I have to see if I can find the article(s).

EDIT:  Not what I had in mind, but discusses the subject

http://wiki.answers.com/Q/Will_you_get_breast_cancer_if_you_wear_a_bra_to_bed

Causality very unclear - I find myself thinking that, for example, the kind of women who don't wear bras much are also (leaving aside the younger women who just don't need 'em) potentially likely to be the kind of women with healthier diet and lifestyle and less stress in their lives (I'm thinking hippy/alternative here). There's no way to tell what's causing what, without a very extensive and careful study.

Quote from: Padma on December 01, 2012, 11:13:03 AM
Causality very unclear - I find myself thinking that, for example, the kind of women who don't wear bras much are also (leaving aside the younger women who just don't need 'em) potentially likely to be the kind of women with healthier diet and lifestyle and less stress in their lives (I'm thinking hippy/alternative here). There's no way to tell what's causing what, without a very extensive and careful study.

Correct, but the original 1990's study showed an association:

That Harvard study fascinated me and I searched the medical literature for possible explanations. In January 1996, I discovered the book by Singer and Grismaijer and their explanation of impaired lymphatic flow intrigued me. I have since read everything that I can find on lymphatic flow. What I have found has amazed me, but that is another story. I can supply you with lots of info if you like. In essence, what Singer and Grismaijer found was that the odds of getting breast cancer dramatically increased with bra-wearing over 12 hours per day.

    Women who wore their bras 24 hours per day had a 3 out of 4 chance of developing breast cancer (in their study, n=2056 for the cancer group and n=2674 for the standard group).

    Women who wore bras more than 12 hour per day but not to bed had a 1 out of 7 risk.

    Women who wore their bras less than 12 hours per day had a 1 out of 152 risk.

    Women who wore bras rarely or never had a 1 out of 168 chance of getting breast cancer. The overall difference between 24 hour wearing and not at all was a 125-fold difference.

The researchers proposed that extended bra-wearing affected the lymphatic system.  Wear a bra fewer than 12 hours per day seems like a cheap insurance policy to me.

That makes some sense.