Ionisers for chronic asthma

Ion generators have been marketed for use in homes to remove dust and smoke particles in order to improve symptoms in people with asthma. Although complex laboratory studies show that ion generators alter airways function, the few studies which have been conducted in the homes of people with asthma, demonstrate no significant benefit in improving lung function or symptoms.

Authors' conclusions: 

Based on the evidence currently available from randomised controlled trials, a recommendation cannot be given for the use of room air ionisers to reduce symptoms in patients with chronic asthma.

Read the full abstract...

Previous reports have shown that ion content in the air may have an effect on respiratory function. Results from studies which test the efficacy of air ionisers to reduce asthma symptoms are often inconclusive and their use as a treatment for asthma remains debatable.


We conducted a systematic review of the available evidence to determine the effectiveness of positive and negative ion generators in people with asthma.

Search strategy: 

We searched the Cochrane Airways Group Specialised Register, Cochrane Central Register of Controlled Trials (CENTRAL) as well as the alternative medicine database AMED. Searches were current as of June 2012.

Selection criteria: 

Randomised controlled trials (parallel or crossover design studies) comparing ionisers with dummy ionisers (being negative or positive ion emitters), in children or adults with chronic asthma.

Data collection and analysis: 

Two reviewers independently assessed titles and abstracts of studies and assessed trial quality. Study quality was determined using two methods:The Cochrane approach to allocation concealment and the five point Jadad scale.

Main results: 

Six studies were selected for inclusion (106 participants). No results were combined as the studies were all of a crossover design.

No study reported a significant difference in lung function between ionised and control air (morning Peak expiratory flow (PEF) - three studies; forced expiratory flow in one second (FEV1) - one study). There were no significant differences in symptoms or beta-2 agonist usage between ionised and control air in three studies.

This study demonstrated that although positively ionised air was associated with a larger fall in FEV1 with exercise, this did not reach statistical significance. Baseline FEV1 was not demonstrated to be significantly different between treatment groups.