Published online: October 10, 2019
Allergies have been increasing rapidly in all areas of the world. However, certain communities seem to be protected, particularly those living in rural areas. It is unknown whether this is caused by factors in the rural environment that are protective against allergies, by factors in the urban environment that increase the risk, or by a combination of these two possibilities.
In a recent study published in The Journal of Allergy and Clinical Immunology (JACI), Levin and colleagues studied allergy outcomes and risk factors in 2 similar populations living in different communities. Children aged 1 to 3 years were randomly recruited from urban Cape Town and a rural community in the Eastern Cape province of South Africa.
The allergy outcomes included the presence of positive blood or skin tests to inhaled and food allergens, and also allergic diseases such as asthma, hay fever, eczema and food allergy. A strength of the study was the use of food challenges to prove food allergy, rather than relying on a history of reactions. Many risk factors were explored, including factors unique to rural and urban communities.
The rural community was strongly protected against all forms of sensitisation and allergy, with about 1/3rd the rate of positive skin and blood tests, 1/5th the rate of food allergy and 1/9th the rate of the other allergic diseases! Interestingly, different risk and protective factors seemed to operate in urban and rural settings. Exposure to farm animals by mothers during pregnancy or as infants was protective against allergies in the rural population. In urban children, birth by caesarean section was a risk factor for food allergy, consumption of fermented milk products was associated with reduced asthma and atopic dermatitis. In both cohorts smoking by mothers during pregnancy and smoke exposure after birth were independently associated with asthma, consumption of fast foods and fried meat were associated with allergy.
Exposure to livestock is the strongest protective factor against allergies in this rural environment. In urban communities, where animal contact is rare, risk factors include caesarean section while protective factors include consumption of fermented milk products. Interventions to prevent increasing allergies in countries undergoing rapid urbanization are urgently needed and could utilize the modifiable risk factors identified in this report.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.