Millions of people start to sneeze in the presence of cats, dust and other triggers. Large numbers of them may have woken up this morning to frightening news - newspaper stories that the five million with allergic rhinitis or hayfever in this country could be at increased risk of Parkinson's disease, writes The Guardian's health editor, Sarah Boseley.
But according to the Parkinson's Disease Society, it isn't true. The story was based on a study carried out in the Mayo clinic in the United States on what is - in the scale of clinical trials - a tiny number of people: fewer than 200 with Parkinson's disease and a similar number without. The researchers looked to see how many in each group suffered from allergic rhinitis. They found that more had the "permanent cold" syndrome in the Parkinson's disease group than in the other group.
What does that mean? According to Dr Kieran Breen, research director of the Parkinson's Disease Society in the UK, it means that Parkinson's causes allergic rhinitis - not the other way round. "It is the biggest scare-mongering thing you can think of," he says. "Five million people with hayfever will think they have a three-times risk of getting Parkinson's and wonder should they give up now?"
He says that it is well known that allergic-type inflammation is associated with Parkinson's disease. It's caused by cells dying and releasing proteins as a result of the disease. "These activate an immune response in the brain," he said. "It is the same with conditions like Alzheimer's. It is the result, rather than the cause, of the condition."
The Mayo clinic study, he said, was not set up to detect a cause. If that had been the case, a large number of people with and without allergies would have had to be recruited and followed up to see how many in each group developed Parkinson's disease.
It's a classic case of the misinterpretation of some fairly marginal science and not wholly the fault of journalists. The actual scientific paper says nothing about allergies being a causal factor in Parkinson's. But the press release is, Dr Breen says, "ambiguous". Comments from the researchers make it clear their interest is in discovering whether people with allergies are more prone to Parkinson's disease - even though their study is not designed in that way. "The investigators theorise that a tendency toward inflammation is the key link between the diseases," it says.
We don't know the cause of Parkinson's disease at the moment - but the Mayo clinic hasn't just alighted on the answer among 200 sufferers. "Although there are likely to be many contributory factors, this study does not establish any convincing causal link between allergic rhinitis and Parkinson's. People who do have allergic rhinitis should not be concerned by the findings of this study," says the society in its official statement.