How to clean mildew
Keep ahead of mildew so it doesn't become a problem. Every six months spray your bathroom ceiling with a 50/50 solution of hydrogen peroxide and water. Peroxide is a safe bleach and won't harm the environment or your lungs. Find larger quantities of peroxide at beauty or medical supply stores.
Spray the mixture on and leave it. No need to rinse or scrub. If you currently have mildew, follow the above directions. Wait two hours and respray. Then wait 24 hours and spray a third time if necessary.