Exam results in Wales could be seriously affected as allergy-related illnesses take their toll on candidates this summer, experts predict.
They called this week for GCSE and A-level exams to be taken at a different time of the year, when allergy sufferers would not be placed at an unfair disadvantage.
Hay fever sufferers are predicted to experience a particularly tough summer because hot dry weather is set to send pollen counts soaring, especially around Welsh coasts.
But bad colds and even swine flu could also contribute to a summer of discontent for candidates.
All exam boards, including the WJEC, have produced contingency plans in case the swine flu becomes widespread.
Any students advised not to go into exam centres because they are displaying flu-like symptoms could be assessed purely on their coursework. But in Wales - where no cases of swine flu had been confirmed when TES Cymru went to press - hay fever is seen as the greatest potential exam spoiler.
The number of children with the condition, which causes sneezing, itching and a runny nose, is rising in the UK. Nearly a third of teenagers are afflicted, it is estimated.
Most sufferers are allergic to grass pollens, which are at their worst during the summer exam season, from May to July.
But forecasters said Wales is likely to be worst hit.
Professor Jean Emberlin, director of the national pollen and aerobiology research unit at Worcester University, said: "In Wales, there are likely to be particularly high counts across coastal strips from Cardiff to Pembroke, up into the Valleys because of the mild winter."
She said this could have a significant impact on pupils' exam performance. "Research shows hay fever can affect concentration," she said. "This can affect students when they are revising as well as during the actual exam."
Research conducted at the University of Edinburgh and Imperial College London in 2007 revealed that GCSE students suffering from hay fever were 40 per cent more likely to drop a grade in their exams than their peers.
"Hay fever is often trivialised because it is not life threatening," said Professor Emberlin. "But it would help if exams were held at a different time of year."
Dr Paul Williams, consultant immunologist at University Hospital of Wales, Cardiff, said the condition could severely affect pupils' ability to study.
"When somebody has hay fever, it's not just about an itchy nose," he said. "What affects most people is the associated feeling of being unwell, like having flu."
He advises teachers to ensure pupils affected by the condition have been to a doctor and received proper medication.
"Make sure the medication is non-drowsy," he said. "The worst (thing) is if somebody who has bad symptoms just accepts it without getting help."
Exam officers are advised to keep a supply of tissues handy for pupils with allergies and, if possible, seat them away from open windows.
All exam boards offer special consideration for illnesses as long as they are sent proof, such as a doctor's certificate.
Pupils suffering from hay fever on the day of an exam could be eligible for 2 per cent more marks, while a severe asthma attack could attract an extra 3 per cent.
Pollen can also trigger asthmatic symptoms. One in nine children in Wales is affected by the condition.
A recent report by Asthma UK Cymru found many pupils stayed off school because teachers did not understand the condition. Sophie Langridge, a spokesperson for the charity, said such absences affected pupils' exam performance.
The exam season in Wales started in earnest last week. The first WJEC exam this summer was taken by candidates on Monday.
The Assembly government is hoping for an improvement in the overall pass rate for GCSE and A-level - 98.4 per cent and 97.6 per cent respectively last year. It is also looking for more A-grades after being outperformed last year by Northern Ireland and England.