Is there anything that you can put into the paint to help prevent mildew?

There are special chemicals that can be added to the paint which are designed to help with this problem. However, it usually involves more than a simple additive if the mildew is an ongoing problem. Mildew will grow in a damp and shady area with poor air circulation. Bathrooms will greatly benefit from an open window and a vent ceiling fan. Other areas may be as simple as frequently cleaning the area.