Assorted asthma inhalers. At top left are spin- halers or turbohalers (white); at centre is a disc inhaler (blue); at lower left and right are aerosol inhalers (grey and brown) and at centre left is a disc with eight capsules together with capsules containing drugs. These devices deliver bronchodilator drugs (drugs which open airways) and/or steroid drugs (drugs which reduce inflammation) directly to the lungs. Aerosol inhalers deliver the drug via a propellant. Disc and spinhalers are activated by inhalation and deliver the powdered drug to the lungs. Asthma is characterised by recurrent attacks of breathlessness which vary in severity.