Female sex hormones called oestrogens may put women at greater risk from deadly allergic reactions, a new study has warned.
The study could explain why men are less likely to be admitted to hospital with severe problems, researchers said.
Researchers at the National Institute of Allergy and Infectious Diseases, US, found oestradiol, a type of oestrogen, enhances the levels and activity of chemical that drives life-threatening allergic reactions.
When people suffer anaphylaxis - an allergic reaction triggered by food, medication or insect stings and bites -immune cells release enzymes which cause tissues to swell and blood vessels to widen, The Telegraph reported.
Although allergies usually only cause flushing or a skin rash, in extreme cases the swelling can lead to even heart attack.
The study found female mice experience more severe and longer lasting anaphylactic reactions than males.
Oestrogen influences blood vessels, enhancing the levels and activity of endothelial nitric oxide synthase (eNOS), an enzyme that causes some of the symptoms of anaphylaxis.
When the researchers blocked eNOS activity, the gender differences disappeared. Giving oestrogen-blocking treatments to female mice reduced the severity of their allergic responses to a level similar to those seen in males.
The study was published in The Journal of Allergy and Clinical Immunology.