Keeping your white bras white requires regular washing. If you tend to wear your bras more than twice without laundering them, you might find they start to yellow or become stained beneath the armpits. Just because your bra is dingy doesn't mean you have to throw it out. Regular chlorine bleach isn't good for bras, but oxygen bleach helps restore them to the same sparkling white as the day you brought them home from the store.
Fill a sink with warm water and add a capful of detergent for delicates. Pour in 1/2 cup of white vinegar. Soak your bra for 30 minutes, then scrub any stains gently by rubbing the fabric of the bra together.
Clasp the bra in back and put it in a mesh lingerie bag.
Set your washing machine for a small load on the gentle cycle. Fill it with warm or hot water.
Add 1 scoop of oxygen bleach and detergent formulated for delicates. Allow the machine to complete the cycle.
Hang your bra to dry in the sun. Remove it from the sunlight as soon as it's dry.
If your bra is white enough after hand washing, there's no need to put it it in the washing machine. Just rinse it and hang it to dry in the sun.
Do not put bras in the dryer, as this can break down elastic and twist underwires. Never wash your bra on the normal cycle or with any clothes other than lingerie. Do not wash your white bra with other colors besides white and ivory.