Sweating
There are special bras designed for sleeping, and they are made of materials like nylon or cotton that can "breathe." However, if you wear your regular bra to bed, you may sweat and the moisture will remain inside the bra. The Teen Growth website warns that this can causing chafing, and in extreme cases you can develop sores.
Discomfort
Daytime bras are designed specifically to support the breasts and shape them properly. Teen Growth says they are not meant to be comfortable when lying down and sleeping. A bra made from firm elastic can feel tight and unyielding. If the bra has underwire supports, they can cut into the skin while you are sleeping. The friction can case irritation, chafing and sores. Teens Health says that a properly fitting bra doesn't need to be restrictively tight. If your bra is causing problems even during the day, get measured at a department store or lingerie shop to make sure you're wearing the right size.
Insomnia
If you wear a daytime bra that is very tight or otherwise uncomfortable, it can keep you from falling asleep. You may be tired during the day because you are not getting a restful sleep. Teens Health says this is the only way that sleeping in a bra can directly affect your overall health. Although some people have an anecdotal belief that wearing a bra overnight can cause cancer, Teens Health says it is completely false.
