This article was last updated on 21 May 2020.
Across Europe, face masks and coverings are becoming commonplace as COVID-19 restrictions ease but health authorities continue to urge caution.
The advice from the World Health Organization (WHO) has remained consistent in recent weeks, recommending masks primarily for medical personnel.
But they say "currently there is not enough evidence for or against the use of masks (medical or other) for healthy individuals in the wider community".
The main recommendation is to save them for those people who have coronavirus symptoms or are taking care of a suspected case.
For countries that are currently considering the use of masks more generally, the WHO advises policymakers to apply a "risk-based approach".
But on social media, rumours have spread rapidly that the use of masks can cause other medical issues related to the respiratory system.
One article in a Nigerian newspaper suggested that prolonged use of face masks causes hypoxia - a condition where the tissues of the body are starved of oxygen.
Another graphic spread across Europe on Facebook, arguing that that prolonged mask usage can cause hypercapnia - another condition arising from too much carbon dioxide (CO2) in the blood.
But both of these claims are inadequately sourced and cited.
A report on social media misinformation in the European Union found that messages "frequently focus on attempting to undermine trust in institutions and governments".
'No impact on CO2 levels in regular individuals'
The WHO had acknowledged in their interim guidance on the use of masks, released in April, that there were disadvantages for wearing a mask, including "breathing difficulties" and a "dependency" on face coverings.
But in a statement to Euronews, WHO's office in Europe have stated that concerns over carbon dioxide intake are doubtful.
"A build-up of CO2 is one of the aspects of wearing a mask that many people find a little uncomfortable, but it is unlikely that wearing a home-made or regular surgical mask will cause hypercapnia," said a spokesperson.
The WHO did say that some medical staff could face an issue when using "close-fitting respirators" as opposed to cotton or cloth facemasks.
It was also noted that recommending the use of face masks could restrict their availability for medical professionals across the world.
"It is possible that mask use, with unclear benefits, could create a false sense of security in the wearer, leading to the diminished practice of recognised beneficial preventive measures such as physical distancing and hand hygiene."
Global health authorities have underlined that masks alone do not provide adequate protection and other health measures should also be adopted.
But Dr Nina Shapiro, professor at UCLA School of Medicine, told Euronews that face coverings "do not have any impact on CO2 levels in regular individuals".
"[N95 masks] have been used for fire/smoke protection, and for workers in construction for many years".
"They are extremely uncomfortable and pretty harsh on the skin, but the notion that thousands of workers are becoming hypoxic and/or hypercapnic is unfounded."
Dr Shapiro explains that this is because respirator particles of carbon dioxide are so small that they will pass through mask material, unlike larger particles of coronavirus.
Masks have 'a substantial impact on transmission'
Other concerns online have focused on the question of wearing a mask during exercise, but medical experts say cloth masks are more recommended for this use.
"They reduce the increased spread of respiratory droplets known to occur with exertion," Dr Shapiro told Euronews.
"Each of these droplets could carry COVID-19 particles - all the more reason to wear a mask."
Breathing in excessive carbon dioxide can be dangerous for the human body, especially for people with pre-existing respiratory illnesses, and face mask warnings are also in place for young children under the age of two and anyone who is unable to remove the mask without assistance.
But medical advice indicates other citizens are in little to no danger of breathing in unhealthy amounts of carbon dioxide by wearing cloth or surgical masks.
Scientists at Arizona State University have further claimed that if 80 per cent of people wore one, it could reduce mortality somewhere between 24 to 65 per cent.
In April, the British Medical Journal also wrote that masks “could have a substantial impact on transmission, with a relatively small impact on social and economic life”.
"It seems like much of Europe is on the same page," says Euronews' Political Editor Darren McCaffrey.
"The political positioning in Europe is moving towards making covering your face and mouth mandatory - particularly on public transport and in crowded places."
"It seems governments are also advising us to wear face masks; not just because they might protect our health but also because they’ve concluded it will make us feel safer as we try to get back to a sense of normality."
Nina Shapiro added that a significant reason for wearing masks is that citizens can unknowingly spread the virus.
"Coronavirus often undergoes a variable period of 'asymptomatic' or 'presymptomatic' stage, for up to several days".
The World Health Organization says they are actively studying the "rapidly evolving" science and are continuing to update their guidance.