The ash falling from a volcano in Iceland is not only dangerous for air travel, the World Health Organization warns it's also dangerous to breathe.
WHO spokesman David Epstein said even the tiniest, microscopic ash is dangerous because inhaled particles can cause respiratory problems.
"We're very concerned about it. We're studying the situation closely," Epstein told reporters in Geneva Friday.
The cloud of ash from the volcano under Iceland's Ejfjallajokull glacier contains irritant gases, such as sulfur dioxide, and fine silica dust, which if inhaled, can reach deep within the lung, Epstein said.
"These particles, when inhaled, can reach the peripheral regions of ... the lungs and can cause problems -- especially for people with asthma or respiratory problems," he said.
So far, the ash cloud is high in the atmosphere, drifting at above 6,000 metres, making it mostly invisible from the ground. But winds and rain will determine where the particles fall and in what concentrations.
Epstein warned the ash would likely cause problems in those with pre-existing lung problems.
"Any particular matter that is deposited (and) breathed into the lungs is dangerous to people," he said. "It depends on how the particles are suspended in the cloud and their density. We don't know that yet."
He added that those with breathing problems should not go outside, if they can avoid it.
"We would recommend that people stay indoors as much as possible," he said, adding that those who venture outside might want to consider a mask.
In Britain, the country's Health Protection Agency sounded a quieter alarm, saying they expected a "small fraction of the Icelandic volcanic plume" to reach ground level Friday night and Saturday morning.
"It is important to stress that the concentration of particles which may reach ground level is likely to be low and should not cause serious harm," the Agency said, adding any health effects from the ash cloud were likely to be short term.
It said people may notice symptoms Friday evening such as itchy or irritated eyes, a runny nose, sore throat or dry cough.
It said if people experience symptoms, notice a dusty haze in the air or smell the rotten egg odour of sulfur outside, "they may wish to limit their activities outdoors or return indoors."
People with existing respiratory conditions such as chronic bronchitis, emphysema and asthma should have their inhalers or medications with them, the agency added.
