Is it a problem (for reasons related to tznius or any other Jewish concern) if a woman does not wear a bra?
Is it still a problem if it is not obvious that the woman is not wearing a bra? Women may wear different kinds of clothing to hide or reveal the fact that they're not wearing a bra.
Please answer with sources.
From the quote below, it seems to me that in some cultures it is not modest not to wear a bra, while in other cultures it is not modest to wear one.
What is the Jewish point of view on the modesty of different breast coverings?
The Wikipedia article for Bra says,
[Some women] simply feel that bras improve their appearance. ... Some women wear bras because they want to conceal the natural shape of their breasts and nipples, responding to cultural standards of modesty, or because they fear criticism or unwanted attention.
Depending on the social context, women may wear different kinds of clothing to hide or reveal the fact that they’re not wearing a bra.
Some researchers have found health benefits for going braless.
In October 2009, Somalia’s hard-line Islamic group Al-Shabaab forced women in public to shake their breasts at gunpoint to see if they wore bras, which they called “un-Islamic”. They told women that wearing a bra was deceptive and against Islamic teaching. Girls and women found wearing a bra were publicly whipped because bras are seen as “deceptive” and to violate their interpretation of Sharia law.