Singulair is used to treat shortness of breath and wheezing associated with asthma attacks. Singulair can also be used to treat symptoms of bronchoconstriction and allergies. Singulair is a leukotriene inhibitor. When you inhale in an allergen such as pollen, your body releases Leukotrienes. These chemicals cause tightening of muscles around your airways and swelling in your lungs, which can result in asthma symptoms. This medication prevents asthma attacks in children as young as 12 months and adults. It also prevents exercise-induced bronchospasm in children who are at least six years old. Singulair can also treat symptoms of perennial allergies in children who are at least six months old and adults. Singulair treats symptoms of seasonal allergies in children who are at least two years old. This medication works by leukotrienes that may worsen or cause allergies and asthma.