Fluctuations in female sex hormones could play a role in the development of allergies and asthma, according to a study published in the Journal of Allergy and Clinical Immunology.

Analysis of studies involving more than 500,000 women highlights a link between asthma symptoms and key life changes such as puberty and menopause.

Further investigation could help explain why asthma is more common in boys than girls in childhood, but more common in teenage girls and women following puberty.

Asthma affects more than five million people in the UK. It is a disease of the airways that can seriously restrict breathing and is often associated with allergies.

Many women report that their asthma symptoms change with their menstrual cycle, which may be down to variations in levels of hormones, including estrogen and progesterone, but the link is unclear.

Researchers at the University of Edinburgh reviewed more than 50 studies of women with asthma from puberty to 75 years of age.

They found that starting periods before turning 11 years old, as well as irregular periods, was associated with a higher rate of asthma.

The onset of menopause – when periods stop and estrogen and progesterone levels fluctuate – was also associated with a higher chance of having asthma compared with pre-menopause.

Scientists say the link between asthma and hormonal drugs including HRT and contraceptives is unclear and women should continue to take prescribed medications by their GP.

The researchers plan to study the biological processes through which sex hormones might play a role in asthma and allergy.

"Asthma and allergy symptoms are often affected by life events such as puberty and menopause, but the reasons behind this are unclear," said Dr. Nicola McCleary, led the study at the University of Edinburgh's Asthma UK Center for Applied Research.

"In fact, there were many differences between studies investigating hormonal treatments in terms of the type and dose of hormone, and the way patients took the treatment. We are now undertaking a project to clarify the role of contraceptives and HRT in asthma and allergy symptoms. "

"Asthma can have a very serious impact on the quality of life and costs of the NHS £ 1bn annually. goal is to undertake a clinical trial to test the effectiveness of hormonal treatments to reduce symptoms of asthma in women," said Dr. Aziz Sheikh, Director of the University of Edinburgh's Usher Institute for Population Health Sciences and Informatics.