Boys are more likely to be diagnosed with a peanut allergy than girls, research has found.
The study in the Journal of Allergy and Clinical Immunology by Edinburgh University researchers analysed 2005 data from over 400 English GP practices.
Children from higher income homes also appeared more likely to be diagnosed.
However, a leading allergy expert said that "inequality of access" to health care could be the reason.
The researchers looked at data on peanut allergies actually diagnosed by a doctor, rather than the actual incidence amongst a population.
The records of a total of nearly three million patients were examined.
Babies and younger boys were up to 30% more likely to be diagnosed with a peanut allergy than girls of the same age, a figure that confirms previous research into peanut allergies.
However, the gap in diagnoses between the sexes narrowed as the children grew up.
By the age of 15, girls and boys were being diagnosed at almost the same rates and by the age of 24 the figures were reversed, with more women being diagnosed than men.
A researcher from the university, Colin Simpson, said that other allergies had shown higher rates in boys than girls too.
The reason for the difference was, he said, still not clear: "There could be a link to the sex hormones, but we don't know for sure. The fact that at puberty there is a change could point to a link, but we need to do more work."
'Inequality of access'
The results also showed that there were more diagnoses in those from higher income groups.
Patients in the highest income groups were almost twice as likely to be diagnosed as those from the lowest income homes. There were 0.7 diagnoses per 1,000 patients in the highest socio-economic group, compared with a diagnosis rate of 0.4 per 1,000 in the lowest.
This appears to confirm the common idea that peanut allergy affects those from the middle classes disproportionately.
But paediatric allergy expert Dr Adam Fox, from the Evelina Children's Hospital in London, said that this was not necessarily the case.
"It's interesting to see this difference but it does not mean that children from middle-class homes are more likely to have peanut allergies.
"It could be that those from more deprived backgrounds are not as good at getting their children diagnosed as those from the middle classes. We know that there is an inequality of access in health care."
Dr Fox said that more work should be done at looking at why the rates were different when comparing diagnoses from children in different income groups.
"Whatever the reason is, it's an interesting finding and we need to find out why these differences are showing up."
Lower prevalence rates
The overall numbers of people with a peanut allergy appeared much lower in this study, than in previous work measuring the amount of peanut allergies in the UK.
Previous studies have a reported prevalence rates as high as 18 per 1000 among children of primary school age. This study showed much lower prevalence rates - of just 2 per 1000.
Researcher Colin Simpson said that the rate was likely to be "somewhere between the two."
Dr Fox said that the difference in the rates could probably be explained by the different collection methods.
Unlike previous studies, this report measured only patients with allergies who had actually gone along to a see a GP and who had been diagnosed as having a peanut allergy.
Dr Fox said that some patients may also have been missed by the study if their allergy had been categorised in the GP records as a food allergy, rather than a peanut allergy.