More than a third of children in the United States live with a tobacco smoker, and allergic diseases are becoming increasingly common among children. Could there be a connection?
A recent study review found that tobacco smoke exposure was moderately associated with nose, skin and food allergies, especially in children and teenagers.
The authors of this review believe that more studies that focus on specific age groups and more detailed definitions of exposure are needed to fully assess the strength of these associations.
The lead author of this review was Bahi Takkouche, MD, PhD, from the Department of Preventive Medicine at the University of Santiago de Compostela in Santiago de Compostela, Spain; and the Centro de Investigación Biomédica en Red de Epidemiología y Salud Pública in Barcelona, Spain.
A total of 196 studies published between 1996 and June 30, 2013. Ninety-seven of the studies were on allergic rhinitis, 91 studies were on allergic dermatitis and eight studies were on food allergies.
Allergic rhinitis is a reaction that causes the inside of the nose to become inflamed due to breathing in allergens such as pollen, dust, animal hair, etc. Symptoms include running nose, sneezing, watery eyes and itchy nose, throat and eyes.
Allergic dermatitis is a skin reaction that happens when the skin is exposed to allergens such as latex gloves, poisonous plants, antibiotics or certain fragrances.
The studies were conducted in 51 countries around the world.
The findings showed that secondhand smoke exposure was associated with a 10 percent increased risk of developing allergic rhinitis when all studies were analyzed together.
When the authors restricted the analysis to adult participants only, they found that secondhand smoke exposure was associated with a 17 percent increased risk of developing allergic rhinitis.
Smokers were 21 percent more likely to develop allergic dermatitis compared to the participants who were not exposed to tobacco smoke (either through smoking or secondhand smoke exposure).
Adult smokers were 14 percent more likely to develop allergic dermatitis compared to adults who were not exposed to tobacco smoke.
Secondhand smoke exposure was associated with a 7 percent increased risk of developing allergic dermatitis for all ages, but was associated with a 26 percent increased risk of developing allergic dermatitis when just considering the adults.
Among the children and teenagers, the risk of developing allergic rhinitis was increased by 40 percent for smokers and by 9 percent for those exposed to secondhand smoke compared to the children and teenagers that were not exposed to tobacco smoke.
Secondhand smoke exposure was associated with a 6 percent increased risk for allergic dermatitis in children and teenagers, and smoking was associated with a 36 percent increased risk of allergic dermatitis.
The findings revealed that participants of all ages exposed to secondhand smoke were 43 percent more likely to develop food allergies compared to participants who were not exposed to tobacco smoke at all when only looking at cohort studies.
Cohort studies follow a specific group of people for a long period of time and focus on outcomes associated with one or more exposures. When looking at all the studies on food allergies together, the authors did not find a significant association between passive smoking and food allergies.
Dr. Takkouche and team also discovered that smoking during pregnancy had no significant effect on the risk of developing allergic rhinitis, allergic dermatitis or food allergies.
The researchers noted a few limitations of their study. First, most of the studies were cross-sectional meaning that the data was on a large group of people at a specific moment in time so the authors could not determine any cause-and-effect relationships. Second, the studies may not have accounted for the same factors that may have influenced the associations. Lastly, participants in the many of the studies self-reported their cases of allergies and their overall smoke exposure.
This review was published on March 11 in PLoS Medicine.
The Institute Carlos III and the Spanish Ministry of Defense provided funding.