Rosie Newbigging, from the charity Asthma UK, says "the vast majority of asthma deaths are avoidable", but people with asthma need to be more aware of the risks they face.
The new figures about how many people underestimate the risk caused by their asthma come from 2,498 Welsh responses to a test set up by Asthma UK.
The charity is urging adults with asthma to take the 'Avoid Asthma Attacks' test.
It says that the test only takes 60 seconds, will reveal someone's risk of having an asthma attack, and tell them how they can reduce it.
Common risks include not taking your preventer inhaler every day, ignoring worsening symptoms and not having a personal asthma action plan.
Asthma UK Cymru says:
- 314,000 people in Wales are currently receiving treatment for asthma - 1 in 10 of the population
- There were 62 deaths from asthma in Wales in 2010
More than 110,000 people in Wales don't realise they are a risk of an asthma attack, according to new research.
Asthma UK Cymru found that 48% of people who took their test, who have asthma, don't think they are at risk of an attack.
The vast majority of those people are wrong, and are at danger, the charity says.
It says the data shows people with asthma considerably underestimate their risk of potentially fatal attacks, and is launching a campaign called 'Stop Asthma Deaths' to try to make people more aware of the danger.
This is not the first time researchers at Cardiff University have made the link between fungi and asthma. Previous research found that removing fungi from people's homes could help improve life for asthma sufferers.
Researchers at Cardiff University say hundreds of tiny fungal particles found in the lungs of people suffering from asthma could help in developing new treatments.
It was previously thought that the lungs were sterile, but a new study undertaken by university researchers has found the presence of large numbers of fungi in healthy lungs.The researchers hope the discovery could lead to new lines of research and better treatments for sufferers in the future.
A charity is calling for asthma sufferers to be more aware of the risks of not treating their condition.
Asthma UK says one in three asthma sufferers in Wales are at high risk of having a potentially fatal attack.
The condition kills around 60 people in Wales every year, with 3,500 admitted to hospital following an asthma attack.
John Mathias, from Asthma UK, called the figures are "extremely worrying" .
"As up to 75% of emergency hospital admissions are preventable with better management and support it's vitally important that the 314,000 people in Wales with asthma understand their condition", he said.