Women are more likely to suffer deadly allergic reactions because of their hormones, a study has warned.
Oestrogen, the primary female sex hormone, worsened allergic reactions in lab tests, researchers found.
When people suffer anaphylaxis – an allergic reaction triggered by food, medication or insect stings and bites – immune cells release enzymes that cause tissues to swell and blood vessels to widen.
This causes skin to flush or develop a rash and in extreme cases, breathing difficulties, shock or heart attack.
The researchers say this new study may explain the differences between the sexes when it comes to allergies.
Previous studies have found women tend to experience anaphylaxis more frequently than men, but why this difference exists is unclear.
The study was conducted by scientists at the US National Institute of Allergy and Infectious Diseases.
They found oestradiol, a type of oestrogen, enhances the levels and activity of an enzyme that drives life-threatening allergic reactions.
The study, published in The Journal of Allergy and Clinical Immunology, found female mice experience more severe and longer lasting anaphylactic reactions than males.
This may be because oestrogen makes an enzyme that causes some of the symptoms of anaphylaxis to become more potent.
This enzyme is called endothelial nitric oxide synthase (eNOS).
When the researchers blocked eNOS activity, the allergy differences between the genders disappeared.
They also found that giving treatments that blocked oestrogen could have an effect.
Female mice given these treatments saw their allergic reactions fall the lower level usually seen in men.
The researchers said the study had identified a clear link between oestrogen and eNOS and severe anaphylactic reactions.
But they added more work is needed to see if the effects are similar in humans.
They hope the findings can now be applied to developing allergy treatments.