The magenta dots at bottom indicate when various parts of the UK made face masks mandatory, initially only on public transport. But then masks were made mandatory in retail shops and other locations. Rules came into place at varying times depending on location: N Ireland, Wales, Scotland, England and so on.
The more that were required to wear face masks, the worse it became – in fact, many times worse. This pattern has gone on around much of the world and there is no unified explanation as to why face masks have failed to curtail the outbreaks.