Iron is a beautiful material, with a very unique character. You can wear iron all the time: take a shower, cook, wash the dishes, have a sauna, have sex or sleep! The main thing to remember is that if you get it wet, you should wipe it dry, as you would do with your hands. Don’t let it dry itself.
At the beginning it may leave a mark on your skin, but after a while your piece will become “oxidized to you" and it won’t leave a mark anymore. Rusting is a natural part of the life of iron and rust absorbs natural oils from your skin, forming a protective layer.
Iron jewellery needs care, just like silver does. Not being a precious metal it is more reactive with the environment and with you. If you get ill it will leave a dark mark on your finger again, probably because of the changed acidity of the skin or your jewel worrying for you. When you swim in the sea the same thing happens and you must rinse it with fresh water and wipe it immediately. I think it is nice to live together with such a strong and sensitive metal.
If you don’t wear the piece for a long time you may notice some rust; this rusting takes less time in humid environments. In this case you need to rub the jewellery gently with a plastic kitchen scourer, wipe it down with soapy water and a sponge, rinse, then dry.