Potentially fatal childhood peanut allergies mainly affect better-off boys, research has shown.
A study found that young boys have higher rates of the condition than young girls, and children from well-off homes are more likely to be affected than those from poorer backgrounds.
More research is needed to explain the trends, say scientists.
The findings, published in the Journal of Allergy and Clinical Immunology, emerged from the health records of more than 400 GP practices in England between 2001 and 2005.
They showed that boys younger than 20 are almost a third more vulnerable to peanut allergies than girls in the same age group.
However, the pattern reverses in adulthood with slightly more women than men being at risk.
Part of the reason may be that after the age of 15 women are more likely to visit their doctor and therefore have the allergic condition detected, say the researchers.
Another possibility is that biological changes linked to sex hormones around the time of puberty might influence immune system-driven allergic reactions.
The highest rates of peanut allergy were found in children between the ages of five and nine.
The research suggests more than 25,000 people in England have been diagnosed with a peanut allergy at some point in their lives, a lower figure than previous estimates.
It is not yet clear whether fewer people are actually being affected or whether the change is due to under-recording of cases by GPs.
Dr Daniel Kotz, who led the Department of Health-funded study, said: "This research has shown that whilst peanut allergy is less common than previously thought, it affects over 25,000 people in England. Having a serious allergy like this can cause great anxiety and stress to those affected. We now need more research to help explain why the condition occurs relatively more often in boys and affluent people."
Peanut allergies commonly cause breathing problems. At their most serious they can trigger life-threatening anaphylactic shock.