At least three West End theatres have reported temperatures of 30C inside or higher this week, according to performing arts union Equity.
It comes as the capital has been gripped by a record heatwave which has seen the mercury rise to 36C in some parts of London on Friday.
Heat warnings are in place, with dozens of schools shutting or partially closing across the working week. But in the West End, the show must go on.
Equity and the Society of London Theatre are now urging production companies and theatres to take action to protect performers and audiences amid rising temperatures.
Speaking to The Standard, a spokesperson for Equity said they are encouraging production companies to adapt costumes, reduce the use of lighting rigs, and carry out thorough risk assessments.
The union added that 27C “should be the cut-off for strenuous work – like performing a number in a musical in full costume.”
Performers have been given thermometers to monitor temperatures at their workplaces.
It is also advising “hydration breaks” inspired by the World Cup 2026; a measure which has already been adopted by production teams at Avenue Q at The Shaftesbury Theatre.
It has introduced three-minute breaks during performances at the Shaftesbury Theatre, allowing the cast to cool down and drink water after performing inside heavy puppet costumes.
Production companies are also being told to push back shows outside of peak temperature hours, for example, moving evening shows to 8pm instead of 6pm.
One musical theatre actress, Alyssa Jaffe, originally from Los Angeles, said London’s heatwave was “something else”, describing it as a “swampy heat”.
“It’s sticky, there’s no air con, and the buildings are double-glazed,” she said, adding that it was far cooler in US theatres.
Ed Bussey, deputy musical director of Jersey Boys, told The Standard that two cast members at the New Wimbledon Theatre performance of the Grammy Award-winning show had to be given ice packs after “feeling unwell.”
He added another crew member had to “duck out the second half” due to heat exhaustion.
The New Wimbledon Theatre, a Grade-II listed building, does not have air conditioning.
However, the majority of London’s theatres do have air cooling systems in place for coping with hot weather.
SOLT has previously said it would be “inaccurate” to suggest that all theatres are unprepared for extreme heat. Many have taken steps to improve and manage rising temperatures.
However, the statement added that investment is required to ensure heating and cooling systems are adequately upgraded, which can be costly particularly in older buildings.
As it stands, the majority of the theatres in the West End are listed buildings.
A SOLT & UK Theatre spokesperson said: “The safety and comfort of audiences, performers, staff and visiting companies remains the priority for SOLT & UK Theatre members, who are taking proactive steps to respond to the current period of extreme heat, adapting operations and working practices where needed.
“Theatres will assess conditions locally and take appropriate action, which may include adapting performance schedules.”
Adam Adnyana, Equity assistant general secretary for live performance, said: “Extreme heat is a serious health and safety issue for anyone in live performance, whether indoors, outdoors, performer, stage management or audience member.
“In the current heatwave – as in previous ones – Equity is providing advice and guidance to members and engagers on safe temperatures, heat mitigation, and sensible adaptations – up to and including rescheduling or cancelling shows in the interests of safety. Sometimes, the show does not have to go on.”
