Is it bad for your breast if you wear a push up bra? will it make your breast sage ?

Push up bras: Will not contribute to sagging as it simply takes the weight off your cooper ligaments in your breast tissue... But not wearing a bra will eventually result in 'coopers droopers'.

It won't lead to: Sagging. While there isn't a definitive correlate, there have been small studies to suggest a link between wearing a bra and breast cancer. Again this hasn't been strongly concluded but food for thought.