A condition in which a person's airways become inflamed, narrow and swell and produce extra mucus, which makes it difficult to breathe. Asthma can be minor or it can interfere with daily activities. In some cases, it may lead to a life-threatening attack. Asthma may cause difficulty breathing, chest pain, cough and wheezing. The symptoms may sometimes flare up. Asthma can usually be managed with rescue inhalers to treat symptoms (salbutamol) and controller inhalers that prevent symptoms (steroids). Severe cases may require longer-acting inhalers that keep the airways open (formoterol, salmeterol, tiotropium), as well as inhalant steroids. This means that asthma can be genetic. Some researchers describe it as a “highly heritable disease.” According to a 2014 review study, genetic factors account for around 70 percent of a person's risk of developing asthma, meaning that genes play a large role in whether or not a person develops the condition.