More than 3,000 students in Wales slept in bedrooms containing the potentially fatal chemical asbestos - because their universities considered it a "low risk".
The British Lung Foundation has condemned the universities' failure to inform the students as "reckless", while the National Union of Students (NUS) urged the institutions to take the issue seriously.
Information passed on to BBC Wales revealed Cardiff, Aberystwyth and the University of Wales Trinity St David all had rooms containing the material.
Cardiff University has 1,500 rooms where asbestos is present, including Talybont North and Aberconway Hall.
A spokesperson for Cardiff said: "As we believe that the control measures and management procedures we have in place sufficiently minimise the risk, we do not advise students where low risk Asbestos Containing Materials (ACMs) are present."
Aberstywth had asbestos in 1,088 bedrooms, while the University of Wales had the material in 443 rooms. Both institutions said they complied with legislative requirements.
A spokesperson for the British Lung Foundation added: "Exposure can often occur unwittingly, and so wherever people live or work they should reliably be informed of the presence of asbestos. Not to do so is reckless."
Asbestos is the single greatest cause of work-related deaths in the UK, according to the government, causing around 4,500 fatalities a year. If inhaled, asbestos fibres can cause serious and sometimes fatal diseases such as mesothelioma and lung cancer.
A spokesperson for NUS Wales said: "We strongly encourage institutions to take this issue seriously and put the safety of students first, whilst ensuring they remain completely transparent with students about the standards of their accommodation."
Previous research revealed universities were keeping students in the dark about the dangerous substance, with Warwick University having 2,313 student bedrooms with asbestos in.
The Health and Safety Executive, a public body concerned with workplace safety, added: "All universities must ensure they have effective arrangements in place to manage the risks so that staff and students are not exposed to asbestos fibres.
"As long as asbestos is managed in compliance with the legal requirements and according to the HSE's published guidance, there is no significant risk in leaving it in place."
If you are concerned about your safety, the HSE can be contacted on: 0300 003 1747