Seretide accuhalers and evohalers contain two active ingredients, fluticasone propionate and salmeterol. Fluticasone is a type of medicine known as a corticosteroid. Corticosteroids are hormones that are produced naturally by the adrenal glands. They have many important functions, including control of inflammatory responses. Fluticasone is a synthetic corticosteroid and is used to decrease inflammation in the lungs. (NB. Corticosteroids are often simply called steroids, but it should be noted that they are very different from another group of steroids, called anabolic steroids, which have gained notoriety because of their abuse by some athletes and body builders.) When fluticasone is inhaled into the lungs it is absorbed into the cells of the lungs and airways. Here it works by preventing the release of certain chemicals from the cells. These chemicals are important in the immune system and are normally involved in producing immune and allergic responses that result in inflammation. By decreasing the release of these chemicals in the lungs and airways, inflammation is reduced. In asthma, the airways tighten due to inflammation and can also be blocked by mucus. This makes it difficult for air to get into and out of the lungs. By preventing the inflammation and excess mucus formation, fluticasone helps prevent asthma attacks. Salmeterol is a type of medicine called a long-acting beta 2 agonist. It works by acting on receptors in the lungs called beta 2 receptors. When salmeterol stimulates these receptors it causes the muscles in the airways to relax. This allows the airways to open. In asthma there is narrowing of the airways. By opening the airways, salmeterol makes it easier to breathe. Salmeterol doesn't open the airways as quickly as short-acting beta 2 agonists such as salbutamol or terbutaline, however, it does keep the airways open for much longer. The effects of salmeterol last for about 12 hours, whereas those of salbutamol or terbutaline last for about 3 to 5 hours. This means salmeterol is used to prevent asthma attacks, wheezing, chest tightness or shortness of breath, rather than to relieve them. This combination of medicines is used for asthma that is not sufficiently controlled by using just a regular steroid inhaler and a reliever inhaler (eg salbutamol). Seretide should be used regularly, even when you have no asthmatic symptoms, to reduce the inflammation in the lungs and to help keep the airways open. You should still keep your reliever inhaler with you at all times in case you do have an asthma attack. This combination inhaler can also be used to treat chronic obstructive lung disease (COPD) such as chronic bronchitis or emphysema. However, the Seretide 500 accuhaler is the only Seretide product that contains the correct dose of active ingredients for this use. Inhaling this medicine allows it to act directly in the lungs where it is needed most. It also reduces the potential for side effects in other parts of the body, as the amount absorbed into the blood through the lungs is lower than if it is taken by mouth.