Asthma in cats is thought to be caused by an allergic reaction to inhaled allergens in their environment. These triggers may include dust, cigarette smoke, pollen, perfume, cleaning products, essential oils, and more. When an asthmatic cat inhales an allergen, it triggers an immune response — specifically, an inflammatory response. This response may cause increased mucus production and airway constriction or spasms, both of which can make it difficult to breathe. While all cats are susceptible to asthma, overweight cats may be more likely to develop this condition, and Siamese cats may be more predisposed than other breeds.