stylistic:tone
Environmental

Many environmental factors have been associated with asthma's development and exacerbation, including allergens, air pollution, and other environmental chemicals. There are some substances that are known to cause asthma in exposed people and they are called asthmagens. Some common asthmagens include ammonia, latex, pesticides, solder and welding fumes, metal or wood dusts, spraying of isocyanate paint in vehicle repair, formaldehyde, glutaraldehyde, anhydrides, glues, dyes, metal working fluids, oil mists, molds. Smoking during pregnancy and after delivery is associated with a greater risk of asthma-like symptoms. Low air quality from environmental factors such as traffic pollution or high ozone levels has been associated with both asthma development and increased asthma severity. Over half of cases in children in the United States occur in areas when air quality is below the EPA standards. Low air quality is more common in low-income and minority communities.

Exposure to indoor volatile organic compounds may be a trigger for asthma; formaldehyde exposure, for example, has a positive association. Phthalates in certain types of PVC are associated with asthma in both children and adults. While exposure to pesticides is linked to the development of asthma, a cause and effect relationship has yet to be established. A meta-analysis concluded gas stoves are a major risk factor for asthma, finding around one in eight cases in the U.S. could be attributed to these.

The majority of the evidence does not support a causal role between paracetamol (acetaminophen) or antibiotic use and asthma. A 2014 systematic review found that the association between paracetamol use and asthma disappeared when respiratory infections were taken into account. Maternal psychological stress during pregnancy is a risk factor for the child to develop asthma.

Asthma is associated with exposure to indoor allergens. Common indoor allergens include dust mites, cockroaches, animal dander (fragments of fur or feathers), and mold. Efforts to decrease dust mites have been found to be ineffective on symptoms in sensitized subjects. Weak evidence suggests that efforts to decrease mold by repairing buildings may help improve asthma symptoms in adults. Certain viral respiratory infections, such as respiratory syncytial virus and rhinovirus, may increase the risk of developing asthma when acquired as young children. Certain other infections, however, may decrease the risk.