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Hay fever is common, and it's becoming more common.¹

• Between 20 million and 40 million people in the United States have hay fever or another allergy with similar symptoms.^{2 3}
• Overall, experts estimate that about 1 in 10 people get hay fever.¹ And studies show that more and more are getting an allergy that gives them a stuffed-up nose or makes them sneeze.¹
• People of all ages and of both sexes have allergies such as hay fever, but more teenagers have allergies than any other age group.⁴

And it's not just hay fever that's becoming more common. Other allergic conditions, such as eczema and asthma, are becoming more common, too. We're not certain why.

One idea is that the increase in allergic conditions is related to people having smaller families and better standards of cleanliness nowadays. This means children don't get as many infections as they used to.^{5 6}

Some researchers think that getting lots of infections when you're young helps strengthen your immune system. So, if children aren't getting so many infections, their immune systems may be affected. This could make them more likely to get allergies.

There's some evidence that first-born children, children from small families and children who don't go to nursery are more likely to get allergic conditions, such as hay fever.⁷ This might be because they get fewer infections in the first few years of their life than children from bigger families and children who mix with lots of other children at nursery. Some doctors may advise parents to make sure their young children mix with other children so that they get infections when they're young.

There's no evidence from research that having your child vaccinated increases their risk of allergic conditions.⁸

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.