Using a blue "reliever" inhaler too much is a sure sign that asthma is out of control - increasing the risk of dying from the condition.

While deaths from asthma attacks are still relatively rare, they do occur - actress Charlotte Coleman was one high-profile casualty of the illness.

Most asthmatics are prescribed two types of inhaler - one designed to relieve the wheezing symptoms, and another to control the condition and reduce the frequency of attacks or prevent them entirely.

Research in the journal Thorax suggests it is possible to spot asthma patients at greatest risk of a fatal attack simply by checking how many "reliever" inhalers they are getting through.

If you are using your reliever this often, you should get along to your GP

Dr Martyn Partridge, National Asthma Campaign

If it is more than one a month, that is a warning that the drug - which opens up the airways of the lung - is being used too often.

The study, carried out in the US and Spain, involved more than 96,000 patients, and revealed that the chance of death from an asthma attack is very small - only 43 in this group over a four-year period.

However, 13 or more prescriptions over a year were associated with a 50-fold increase in this risk of dying.

Between seven and 12 prescriptions over a year was linked to a 16-fold risk.

Conversely, the more often the "preventer" inhalers were prescribed, the less likely a fatal attack was.

No danger

Experts were keen to stress the study did not suggest that reliever medication itself was dangerous, simply that over-use showed how out-of-control the asthma was.

Dr John Harvey, from the British Thoracic Society, said: "This research clearly demonstrates just how important it is for asthma patients to use both 'reliever' and 'preventer' medicines if they are prescribed by their GP.

"Both can have their place in managing mild and severe asthma correctly."

He added: "The British Thoracic Society would advise any patient concerned about their use of relievers as part of their asthma management plan to talk to their GP or asthma nurse."

'Rust spots'

Dr Martyn Partridge, from the National Asthma Campaign, likened the over-use of relievers to painting over rust spots on a car.

He said: "What this study shows is that preventer medication really works.

"However, the public have a slight phobia about steroids, and tend to prefer the reliever inhaler because they can feel it working.

"If you are using your reliever this often, you should get along to your GP and get your asthma under control."

Advice is available in the UK from the National Asthma Campaign on (0845) 7010203.