More siblings, less hay fever: more evidence

Area of Science:

• Immunology
• Epidemiology
• Environmental Health

Background:

• Allergic rhinitis, including hay fever, is a growing public health concern.
• Previous research suggests a lower prevalence of hay fever in children from larger families.
• The 'hygiene hypothesis' proposes reduced early-life exposure to pathogens may increase allergy risk.

Purpose of the Study:

• To investigate the association between sibling number and the prevalence of hay fever and perennial rhinitis.
• To examine the influence of family size on allergic rhinitis symptoms in adults.

Main Methods:

• A large-scale cross-sectional study involving 34,362 individuals over 14 years of age from 26,100 randomly selected households.
• Data collected via questionnaires on hay fever and perennial rhinitis symptoms.
• Logistic regression analysis used to assess the relationship between sibling number and disease prevalence.

Main Results:

• 19.3% of participants reported hay fever symptoms, and 6.0% reported perennial rhinitis.
• Individuals with two or more siblings had significantly lower odds of suffering from hay fever compared to those with no siblings.
• The protective effect of sibling number on hay fever decreased as the number of siblings increased.
• No significant association was found between sibling number and the prevalence of perennial rhinitis.

Conclusions:

• Increased sibling number is associated with a reduced prevalence of hay fever, but not perennial rhinitis.
• These findings provide further support for the 'hygiene hypothesis' in the context of allergic rhinitis.
• Environmental and immunological factors related to family size may play a role in allergy development.