In these cases, the correct course of action is to isolate the item. You can keep it safely once it’s packed up, but don’t keep it packed away for long, because the damage will continue in the microclimate inside the package. Paper that has become damp and has active mould growth must be dried before the loose mould can be removed. This should be done outside in dry weather.

You are correct that mould is a health hazard. As long as the item is kept isolated, there’s not generally any risk in keeping it at home, assuming the package is airtight. If you’re going to try to remove the mould yourself, you must wear protective equipment. I highly recommend that you obtain the help of a conservator to disinfect and conserve the work. Hopefully you will then be able to hang it back on your wall. But of course this depends on the seriousness of the problem. If mould lives for long enough in paper, it can disintegrate the paper completely. And even then there will still be mould spores that can cause health problems. Stains and discolouration can also be caused by damp and mould damage. You can find a conservator by looking on the NKF-N website.

Kind regards from Alexandra, paper conservator