If you believe the posters which (rather oddly) seem to be displayed in the gents' toilets in every motorway station across the country, they're absolutely lethal.
However if you believe most scientists, they're almost certainly harmless.
The World Health Organisation isn't definitive on the matter though, as it classes ALL radio signals as '
possibly carcinogenic'. It says exactly the same thing though about using talcum powder or eating gherkins!
https://www.bbc.co.uk/news/world-europe-48616174