National No bra day encourages women to not put on their bras as a means to encourage breast cancer awareness. It is celebrated on the 13th of October, the month of national breast cancer awareness. No bra day is in the middle of The Big Pink, the national fundraising month with breast cancer care.

No bra day is the movement that started in 2011 and took place on social media where women use the #nobraday to campaign. https://breastcancernow.org/search/google/information%20support%20have%20i%20got%20breast%20cancer%20signs%20symptoms%20breast%20cancer%20checking%20your%20breasts