Hi Harrison,
 
Thank you for your question. If a mattress encasement or protector is designed to prevent mould and mildew, in theory, it should prevent the mould spores from leaving the mattress. That said, as mould is caused by a moist environment, sealing in the mould on your mattress will not prevent mould spores from attaching to other surfaces.
 

 
Mould spores are hazardous to your health. It is recommended to thoroughly clean the mattress by vacuuming both sides of the mattress and emptying your vacuum. Using warm soapy water and a damp cloth, clean the affected area and allow it to fully dry.
 

 
A dehumidifier can remove moisture from the air and regularly ventilating the room by leaving the window open can help prevent the build-up of mould in your home. With proper care and maintenance, you can extend the lifespan of your mattress.
 
I hope this helps and if you would like any further information please do not hesitate to contact the office on 0161 437 4419.
 
Kind Regards
Michaela