My husband left a cleaning cloth pressed against the edge of the laundry basket - it was soaked in antibacterial cleaner, not water (side note, what else do people do with used cleaning cloths to stop toddlers getting at them?!). It was there for about 3 hours before I saw it and moved it. We don't ever shut the lid to the basket so that it airs suitably. A day later I noticed these white marks where the cloth was. Could this be mould (my husband reckons it's "impossible" since it was cleaning fluid rather than water on the cloth but I'm not so sure!) or is it more likely it's some other stain/ residue/ dirt that's coincidentally appeared (or, appeared from the same cleaning cloth!)?!