Most of the teenagers have this question in mind, does sleeping without bra effect breast size?
Answer tho this question is No, but there are many pros and cons of wearing a bra during night.
Major problem with bra sleeping is breast cancer risk. Bra-wearing has been linked to breast cancer in a study done by Sidney Ross Singer and Soma Grismaijer. They found, for example, that women who wore a bra 24 hours a day had a 113-fold increase in breast cancer incidence compared to women who wore bra less than 12 hours daily!
They suggest that bras exert enough pressure to the breast and surrounding areas to inhibit the flow of lymph, which then causes toxins and other waste material to remain in the breasts instead of being flushed out.
Some women want to wear a bra to bed because they think it feels more comfortable. Your best bet is to choose a lightweight, non-underwire bra, if you are comfortable with bra only