I have always heard that sleeping with a bra on can cause breast cancer, is this true?

No. It is not true that sleeping with a bra on causes breast cancer. It's good for your breasts to have good circulation, like all parts of your body, so wear a bra that fits well and does not bind you anywhere.
No. This was invented by a lone anti-brassiere crackpot in the mid-1990's. It's now all over the internet. It's simply made up. Ignore it.
Absolutely not. Whether you wear a bra all the time, or none of the time, or anything in between - has nothing tyo do with developing breast cancer.
No. There has been no scientific evidence that sleeping with a bra on causes cancer of any kind, including breast cancer.

Related Questions

I wear a bra all day and all night when I am sleeping, could this cause breast cancer?

Choice of. Garments have not been shown to cause breast cancer. In a large breast, early detection could be a problem, however. So have your screening tests performed according to prescribed schedule. Read more...
Not true. This screwy claim was made up with no basis by a single anti-brassiere militant in the 1990s. Ignore it. Read more...

Is always sleeping with face down can cause breast cancer?

Never heard, but... Where and how did you get or hear this concern for this question? Based on my 46-year study and practice in medicine, I have never heard or read about your concern on Face-down sleep may cause beast cancer. Physiologically, positioning in sleep should not alter the arrangement of chromosome of any cells inside the body. Hence, the answer to this Q is no; don't worry but stress healthy lifestyle... Read more...
No. I'm actually familiar with this silly myth, which was made up out of whole cloth as an internet hoax in the 1990's militant by an anti-brassiere militant. I'm sorry anyone troubled you over this. Read more...