The number of men with allergies has been consistently increasing over recent decades, a study says.
Footballer Paul Scholes has fronted asthma campaigns
From the early 1970s to late 1990s the numbers affected rose by about a tenth, the report in the British Medical Journal said.
The team from the Wolfson Institute of Preventive Medicine in London was not able to explain the findings.
Past studies have concentrated on the increase in allergies among children, with adults seeming less susceptible.
Lead researcher Professor Malcolm Law said: "It seems to be getting more common because something is changing in people, making them more sensitive, not because there is more grass pollen in the air or anything like that.
"We don't know why they're getting it, but it's something in the people, not the environment.
"Older people are less likely than younger people to have the predisposition.
"But that's not because they had it and lost it when they grew older; it's because they never had it."
About 15m people in the UK have an allergy, although a greater proportion of children are susceptible than adults.
Child nut allergies, which can be fatal, have tended to dominate the headlines, although Manchester United footballer Paul Scholes has fronted asthma campaigns in recent years.
Scientists took blood samples from 513 men attending a medical centre at three different points between 1975 and 1998, the British Medical Journal reported.
They tested the blood for sensitivity to a mix of 11 allergens, including grass pollen, pet skin flakes and house mite dust.
The positive samples were also tested for reactions to inhaled grass, tree and cat allergens.
At the beginning of the period 30% of men had allergic reactions, but by the end 42% were vulnerable.
Researchers found the men had become more sensitive to both indoor and outdoor allergens, allowing them to conclude the results were caused by increased exposure to allergens.
Peter Baker, director of the Men's Health Forum, said the findings were surprising.
Mr Baker said: "I didn't know allergies were a problem for men, and would be keen to talk to the allergy support groups and experts about the results.
"Men of all ages are not very good at accessing health services so it may be that there are lots of men who are suffering from the symptoms in silence.
"We need to market health services to men to make them more attractive."