WASHINGTON : Poorly fitting face masks greatly increase the risk of infection from airborne diseases like COVID-19, compared to custom-fitted masks, according to a study.Researchers at the University of Cincinnati in the US used CT scans of three different-sized face masks attached to three different-sized dummy heads to measure the gaps between the face and the fabric.They then calculated the leaks from these gaps to determine the infection risk.The study, published in the journal Scientific Reports, found that poorly fitting N95 masks can have substantial leaks around the face that reduce their effectiveness and increase the risk of infection."Many people do not realise that the fit of face masks can vary.