The present review aims to identify and summarize epidemiologic investigations published during 2011 on the environmental risk factors for asthma.

Potentially eligible papers were identified by a MEDLINE search. In total, 1,130 items were retrieved. Based on a broad definition of environment, the following topics were included: obesity, diet, vitamin D, air pollution, farming environment, and social factors.

Some of the more relevant contributions included evidence that

1. obesity precedes asthma,
2. fruit consumption is longitudinally associated with a lower risk of asthma and atopy,
3. a comprehensive statewide smoking ban was followed by a reduction in hospital admissions for asthma,
4. asthma is one of the diseases showing the largest burdens due to environmental tobacco smoke,
5. traffic-related urban air pollution is associated with bronchial inflammation as measured by fractional exhaled nitric oxide and uncontrolled asthma,
6. aeroallergens and desert dust may contribute to the short-term effects of air pollution and asthma,
7. and maternal exposure to air pollution before and during pregnancy may alter the immune competence in offspring.