Nepal, Aug. 25 -- As dark clouds roll over and monsoon downpours begin, Nepalis brace for familiar disruptions: flooded streets, landslides and waterborne illness. Nepal currently endures the peak of its monsoon season, with the Kathmandu Valley recording around 500 mm of rainfall in July alone, a deluge that has submerged streets and drainage systems. But in the old timber-framed homes of Bhaktapur, in the rented flats of Kirtipur and Thamel, something equally perilous is quietly taking root in our walls, on furniture, and deep within our damp structures: indoor mould.

Long dismissed as a seasonal stain or a musty smell to be wiped away before guests arrive, mould slowly poisons the air of our homes and accumulates silently in our bodie...