Asthma rates among children have quadrupled since the 1970s, according to a major new survey.
The 30-year study was carried out in south Wales
More than 2,700 children from schools across south Wales were involved in the 30-year research project carried out by experts at Cardiff University.
The findings are being published at a meeting of the British Thoracic Society (BTS) in London on Wednesday.
Dr Michael Burr, who led the survey, said more than 1.4m children across the UK suffered from asthma.
The first study, which was carried out in 1973, diagnosed asthma in 5.5% of the children.
By 1988, that had risen to 12%, and had increased to 27.3% in 2003.
The results contradict other recent research which indicated the number of asthma cases had levelled off.
Dr Burr, epidemiologist at the University Hospital of Wales, in Cardiff, said: "Just when we thought we may have turned a corner, our research shows that asthma prevalence has in fact rocketed in the last 30 years.
"It is possible that asthma prevalence peaked in the 1990s but this study confirms that we cannot be complacent.
"With over 1.4m children suffering from asthma in the UK, we all need to have a better understanding of the condition and measures to combat it."
Asthma kills around 80 people, and affects more than 250,000 in Wales every year.
Jodie Payne, 14, from Cardiff, who is currently in the University Hospital of Wales, following an asthma attack, told BBC Radio Wales: "It's really frightening, because it stops you from breathing.
"Sometimes it can be really scary, I don't know whether I'm going to live or what's going to happen to me.
"I enjoy sports and doing things with my friends, but I can't do it because of my asthma.
"It's upsetting knowing they can do things that I can't.
"I feel pushed out - it's not a normal life for me."
Jodie's mother, Debbie Payne, told BBC Radio Wales about the latest attack her daughter had suffered.
She said: "It was very scary, she was very pale and was on the floor gasping for air.
"She started to have a panic attack as well.
"To be honest, I did think for one minute that I might have lost her."
Ms Payne added that the family's home life had been affected by her daughter's asthma.
She said: "I've got to go home and make sure everything is more or less perfect - keeping the house free of dust, hair everything.
"You can't have carpets and you've got to make sure your wooden floor is spotlessly clean.
"Even simple things like teddies she's been told not to keep anymore.
"It affects the way you live - it's not nice seeing her have to stay home as often as she does.
"You can't send a child to school if they can barely walk to the bus stop because she can't breathe."
The research team at Cardiff University also found a decline in exercise-induced asthma between 1988 and 2003.
This is thought to be as a result of a greater use of inhaled corticosteroids, which are a group of anti-inflammatory drugs used to treat asthma and other lung diseases.
Between 1988 and 2003, the study found the percentage of children using inhaled corticosteroids rose from 2.5% to 11.3%.
Professor Andrew Peacock, from the British Thoracic Society (BTS), said the UK had among the highest rates of asthma in Europe.
He said it placed a huge economic and health burden on the NHS and said the respiratory community would be "extremely concerned" by the study.
"We must tackle asthma on a number of fronts, including vital research into possible genetic causes to helping asthmatics to self-manage their condition," he said.
"We would also urge appropriate use of preventative treatments as this study shows that their use can be beneficial."
The BTS winter meeting is being held at London's QE2 conference centre.