Nearly 20 major healthcare bodies are appealing to the PM for better personal protection against coronavirus.
They say at least 930 health and care workers have died of Covid-19 and more are experiencing long-term effects.
In a letter, they say measures to stop airborne spreading are "inadequate" and call for urgent improvement in masks and other defences against variants.
The government said it was monitoring evidence on airborne transmission and would update advice "where necessary".
The organisations involved represent a wide range of health professionals, from doctors and nurses to dieticians and physiotherapists.
Their approach to Downing Street follows repeated efforts to raise the issue with others in government.
With health and care workers at three to four times greater risk of becoming infected than the general public, the plea to Boris Johnson is to make an "urgent intervention to prevent further loss of life".
It says current policies focus on contaminated surfaces and droplets - for which the best defences are hand hygiene and social distancing - but not on airborne transmission by tiny infectious aerosols.
"There is now no scientific doubt," the letter states, "that Covid-19 spreads via the airborne route."
"The evidence is clear - and lives continue to be put at risk."
The groups are demanding:
- ventilation is improved
- better respiratory protection, such as FFP3 masks, are provided
- healthcare guidance reflects the evidence of airborne transmission
Dame Donna Kinnair, chief executive and general secretary of the Royal College of Nursing, told BBC Radio 4's Today programme that nurses needed better protection when working with patients outside of intensive care units - such as in homes and open wards.
"While we've taken care of one area, people are unnecessarily exposed," she said.
"We need a different approach that recognises the evidence. There is no point in [the UK's four chief medical officers] saying that 'we're writing this guidance all together' if the guidance doesn't adequately protect the people that are working on the front line day in and day out, and we believe it doesn't."
One of the organisations involved, the Royal College of Speech and Language Therapists, says its members routinely have to spend time close to Covid patients.
Chief executive Kamini Gadhok told BBC News: "I'm shocked. I feel quite distraught from it all.
"People are dying - and there is this stonewalling in the context of this being a life-threatening virus.
"Not being heard for so long is incredibly distressing."
It's hard to keep track of the number of appeals and letters leading healthcare organisations have produced in their efforts to secure safer conditions.
And it's not often seasoned health professionals end up in tears when talking about this.
But months of trying to persuade the powers that be to routinely allow a higher grade of personal protection equipment (PPE) for all staff dealing with Covid patients have got nowhere.
One result is an increasing sense among front-line staff of fear about the dangers they face, and of alienation from those deciding the policy on infection control.
Another is that all over the UK, there are growing numbers of hospitals and ambulance trusts quietly going their own way, providing better equipment regardless of the official guidelines.
There's a more fundamental point as well - with a division between those who insist the virus can be held at bay mainly by hand hygiene and droplet control, and those who look at the research into aerosols and judge enough is known to recognise a real risk.
Initially, the concern was many of the staff's tasks - assessing the ability to swallow, for example - were likely to cause coughs and therefore aerosols.
But as the pandemic unfolded, and more research emerged into how the virus could spread, a broader worry surfaced about being in poorly ventilated rooms for long periods protected by only a surgical mask.
A government spokesman said the safety of NHS and social care staff is a priority and that because good ventilation can reduce the risk, there's guidance on it for businesses and health and care settings.
"The government will continue to closely monitor new and emerging evidence on airborne transmission, and update our advice where necessary," he said.
Groups to have signed the letter include:
- Kidney Care UK
- the British Association of Stroke Physicians
- the British Dietetic Association
- the College of Paramedics
- the British Medical Association
- the Chartered Society of Physiotherapy
- the Royal College of Midwives