Due to its similarity to chronic obstructive pulmonary disease (COPD) in humans, this condition in horses has also been called COPD of horses for many years, but thanks to recent scientific knowledge, now it is adopted a new, more appropriate name - Recurrent Airway Obstruction (RAO). RAO is a disease that most often affects older horses kept in stables exposed to environmental allergens (organic dust, microorganisms, endotoxins, mold). Immediately after exposure to allergens, an immune response occurs. The effect of T cells is achieved by secreting inflammatory mediators, which are further responsible for the development of inflammation and the activation of leukocytes in the airways. Activated inflammatory cells respond with a respiratory burst, resulting in the release of reactive oxygen species (ROS). ROS modulates the activation of transcription factors such as nuclear factor kappa B (NF-κB) and activator protein-1 (AP-1) in bronchial epithelial cells, alveolar macrophages, neutrophils, and mast cells. Respiratory inflammation, especially the accumulation of neutrophils and their products, causes changes in mucus properties as a result of changes in the quality and quantity of mucin. Abnormal glycosylation of mucins has been shown to increase the viscosity of airway secretions failing mucociliary function, mucus accumulation, and airway obstruction. Respiratory remodeling is a major factor in the development of irreversible airflow disorders and includes goblet cell and mucous gland hyperplasia, subepithelial fibrosis, neovascularization and an overall thickening of the airway wall. Clinical signs are a result of resistance to the airflow in the airways. Cough, nasal discharge, increased respiratory effort, and sometimes tachypnea may occur. If larger amounts of mucus are present in the airways, abnormal breath sounds can be heard. In chronic cases, hypertrophy of the external abdominal oblique muscle develops which is colloquially known as the "heave line". The working capacity of affected horses is reduced. Severely affected horses may also exhibit inappetence and weight loss. Diagnosis is usually based on anamnesis and clinical signs. Examination of blood gases in affected horses showed lower PaO2 and physiological or slightly higher PaCO2 values. Thoracic radiography shows peribronchial infiltration and enlarged lungs. For a safe diagnosis of RAO, bronchoalveolar lavage (BAL) is used. The basis of prevention and treatment of RAO is environment management, especially dust reduction and improvement of air quality. Corticosteroids and bronchodilators could be administered systemically or by inhalation. Dust consists of plant fragments, mites, bacteria, spores, molds, yeasts, and endotoxins. Its composition is largely influenced by the type and form of animal feed, bedding, the activities of workers in the barn (cleaning, grooming, etc.), and the activity of the animals themselves. The retention of dust in the air and the likelihood of inhalation into different regions of the horse's respiratory tract are influenced by the amount and rate of releasing the small fragments from the bedding and forage, as well as the size of the particles and the rate of their removal by ventilation. Management procedures such as feeding with a pelleted food, usage of wood shavings for bedding and removing the animals from the barn during cleaning could minimize the exposure of horses to airborne contaminants. New constructions should seek to maximize the natural ventilation of the building as well as the distance from potential pollution sources such as busy roads.