It is a truth universally acknowledged that anything the Duchess of Cambridge wears sells out. In the past week, the so-called “Kate effect” was put to public health use when she was photographed, for the first time, wearing a face mask. The £15 mask, from the London-based childrenswear brand Amaia, swiftly sold out, while the digital fashion aggregator Lyst reported a 185% spike in searches for “floral”, “Liberty print” and “ditsy print” face masks within 24 hours. The cheering pink and cream face covering seemed carefully chosen, its delicate Liberty floral pattern recalling 1940s tea dresses, cucumber sandwiches and bunting. The overall optics were carefully choreographed, too, the mask being paired with a colour-coordinated cream dress for a visit to the Baby Basics charity in Sheffield on Tuesday, and with a rose-printed pink and blue dress for a visit to a care home in the city. There Prince William also wore a mask, in a complementary shade of cornflower blue. Wearing jolly, upbeat masks, and coordinating them with an outfit, has become something of a trend. Celebrities and instagram influencers have been experimenting with the visual possibilities of masks for months, sometimes to encourage others to do the same – posting pictures with the hashtag #wearadamnmask, often for the purpose of showing off rather than in the interest of public health. Jennifer Lopez has worn sequins, Reese Witherspoon pink gingham, while Katie Holmes has been papped making ditsy print masks look fashionable, with a topknot, on the streets of LA. Lizzo went as far as to wear a bikini, face mask and gloves in matching hot pink and grass green pineapple print. Overseas, heads of state and politicians – including Queen Mathilde of Belgium and Nancy Pelosi in the US – have been matching brightly coloured floral masks to their dresses in an effort to encourage mask-wearing among the public. British royals have been slower on the uptake, perhaps unsure of where face mask-wearing sits with their MO of visibly emoting and making small talk. The first royal in the UK to be photographed in a mask was the Duchess of Cornwall, who wore a royal blue peacock Liberty print fabric last week. The Duchess of Cambridge’s latest endorsement may be more significant than it at first seems, making mask-wearing look good just before the rules were extended to galleries, cinemas and places of worship on Saturday.