GENEVA (AP) - Europeans should try to stay indoors if ash from Iceland's volcano starts settling, the World Health Organization warned Friday as small amounts fell in Iceland, Scotland and Norway.
WHO spokesman Daniel Epstein said the microscopic ash is potentially dangerous for people when it starts to reach the Earth because inhaled particles can enter the lungs and cause respiratory problems.
"We're very concerned about it," 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 also said Europeans who go outside might want to consider wearing a mask.
Other experts, however, weren't convinced the volcanic ash would have a major effect on peoples' health and said WHO's warnings were "hysterical." They said volcanic ash was much less dangerous than cigarette smoke or pollution.
Volcanic ash is made of fine particles of fragmented volcanic rock. It is light gray to black and can be as fine as talcum powder. During a volcanic eruption, the ash can be breathed deep into the lungs and cause irritation even in healthy people. But once it falls from a greater distance - like from the cloud currently hovering above Europe - its health effects are often minimal, experts say.
The Icelandic volcano that erupted Wednesday has sent an enormous cloud of microscopic basalt ash particles across northern Europe, grounding aircraft across continent. It is drifting above 20,000 feet (6,000 meters), high and invisible from the ground.
"Not all particles are created equal," said Ken Donaldson, a professor of respiratory toxicology at the University of Edinburgh, who has studied the impact of volcanic ash in people. "In the great scheme of things, volcanic ash is not all that harmful."
Donaldson said most Europeans' exposure to volcanic ash would be negligible and that only those in the near vicinity of the Icelandic volcano would likely be at risk.
"Once the volcanic particles are in the stratosphere, they're getting massively diluted because there's a lot of air and other particles blowing around," he said.
He said after previous volcanic eruptions, little impact has been seen in people's health, except for those with lung problems who were close to the volcano.
Dr. Stephen Spiro, a professor of respiratory medicine and deputy chair of the British Lung Foundation, said the further the particles travel, they more diluted and less dangerous they will be. "The cloud has already passed over northern Scotland and we haven't heard of any ill effects there," he said. Spiro said to wear masks or stay indoors to avoid volcanic ash was "over the top" and "a bit hysterical."
"If this was really coming down, you'd see a yellow (tinge) in the air from the sulphur," he said. "But we've seen no sign of that."
Britain's Health Protection Agency said the concentration of volcanic particles that might settle on the ground was likely to be low and should not cause serious harm. The agency said people with respiratory problems like bronchitis and asthma might experience more symptoms like itchy eyes, a sore throat and dry cough. It advised those people to carry their inhalers or medicines with them and said any health effects were likely to be short-term.
Experts said the irritants in volcanic ash were likely to be very diluted by the winds by the time they hit continental Europe, and that any rainfall would also lessen their effects.
"People with health problems shouldn't sit around outside looking up at this cloud because there could be microscopic particles falling down," said Dr. Pascal Imperato, dean of the public health school at the State University of New York Downstate Medical Center, who worked on the response to the eruption of Mount St. Helens in 1980. "But for most people, they will not experience any major breathing or other difficulties."