Irregular menstrual cycles may increase a young woman's chances of developing allergies and asthma. That's the conclusion of an article published in the journal Thorax.

Researchers in Norway surveyed 6,100 non-pregnant women and followed them for eight years. In women ages 26 to 42, irregular periods raised the risk of asthma by 54 percent.

Irregular periods raised the risk of hay fever by 29 percent -- a huge increase.

Older women did not have a clear link between their periods and health.

This study and others have found that female sex hormones can affect a woman's chance of developing allergies and asthma. For example, a third of pregnant women with asthma stay the same, a third get worse and a third get better because of their different sensitivity towards hormones.

Some women get worse asthma and allergies just before their periods, when their hormones change.

Women with allergies and asthma should discuss the situation with their physician. A better understanding of hormones could lead to better treatments in the future.