How can I paint an exterior metal door to withstand high humidity?

https://www.hometalk.com/diy/paint/furniture/q-how-do-i-paint-a-metal-entry-door-to-withstand-extreme-heat-sun-1709436

https://www.wikihow.com/Paint-a-Steel-Door

Hi Mamamia, you can clean it well and sand it, then coat it with a coat of KILZ to prep it for the metal paint, Kilz will stop mold and mildew from growing

Hi ! First clean your door well , make sure to remove all signs of mold . Scuff the door with a sanding sponge , remove all dust with a lightly damp cloth or better yet , tacky cloth , found in paint section . Make sure door is completely dry , then cover the window area , sealing the area with painters tape . Then use rustoleum spray paint , make sure it is for outdoor use and for use on metal.

then paint the door , 2 light coats are better than 1 heavy coat ! Let dry completely before doing the next coat . Then use a rustoleum clear coat , also an outdoor type , good on metal . I would , again do 2 light coats . You need to pick a dry sunny day to do this project , the paint will dry much faster . Good luck !

Go to Sherwin Williams and get the door paint that is formulated for this type of exterior door. They can also add an inhibitor to paint for the bathroom so perhaps they can add it to exterior door paint as well.