CHILDHOOD asthma rates have gone down by one-third over the past decade, according to a respected study.

Experts say there are likely to be a number of reasons for the drop, including more careful diagnoses and possibly the ban on smoking inside public places.

They also report that levels of hay fever and eczema have remained fairly consistent over the last 10 years.

Asthma is typically thought of as being an allergic condition, and allergies also cause hay fever and eczema.

The researchers, who are based in Aberdeen University, said that if asthma rates are dropping and hay fever and eczema are not, it suggests that allergy may not be that important to asthma after all.

The research is known as the Aberdeen School Asthma Study. It is the UK's oldest asthma survey and was first conducted 51 years ago when the rate of the condition was just 4.1 per cent. Levels peaked at 29.5 per cent prevalence in 2004 and fell to 18.6 per cent in 2014.

Nearly 4,000 surveys completed by parents of children at 41 schools across Aberdeen provided the latest findings, which are described in the British Medical Journal Open.

Asthma is the most common chronic childhood medical condition worldwide and the researchers said their findings act as an effective barometer for asthma rates in children across Western Europe.

Dr Steve Turner, senior clinical lecturer in child health at Aberdeen University, said: "There are likely to be a number of contributing factors to the drop in instances of asthma among school children in Aberdeen, and indeed across Western Europe.

"Some of the apparent drop is down to more careful diagnoses being made nowadays. In years gone by asthma was perhaps being diagnosed more freely than it ought to have been.

"There have also been clear changes in our environment - from diet, to the air we breathe. Some might even be tempted to say the smoking ban could be part of it, but we don't know for certain."

Graham Devereux, professor of respiratory medicine at the university, said: "Prevalence of asthma is down - but is still nearly double the rate it was in 1989 (10.3 per cent) and is far higher than the rate recorded 50 years ago in the first study (4.1 per cent).

"These surveys have given us incredibly helpful insights to asthma prevalence in Aberdeen over the years. And if you plot that prevalence over time against other studies, asthma frequency elsewhere shadows that in Aberdeen with uncanny precision."

The questionnaire used by the study has not been changed in the 50 years since it was first sent home with Aberdeen school children. It is thought three generations of the same family have helped the researchers by sending back their answers. Just four questions are used to find out if children are suffering from asthma, hay fever, eczema or wheeze.

The charity Chest Heart and Stroke Scotland (CHSS) has supported the work with funding of nearly £60,000.

Lorna Stevenson, respiratory co-ordinator for CHSS, said: “Whilst it’s good news that rates of asthma have fallen in the last 10 years, nevertheless it’s important that teachers and the parents of children with asthma have a good understanding of the condition and how to keep children healthy and safe.

“CHSS is delighted to have funded this important study and we have recently launched a new website, www.mylungsmylife.org for people with COPD and asthma. This includes practical advice and information for the parents of children with asthma.”