Electric fans for reducing adverse health impacts in heatwaves

Heatwaves are generally considered to be hot weather events that breach regional or national norms, and last for several days. Climate modelling suggests that they are likely to become more frequent as the twenty-first century progresses, with attending infrastructure and public health consequences. The economic, environmental and social impact of heatwaves is already well documented, but less is known about the effects, both beneficial and harmful, of interventions designed to mitigate the effects of extreme heat.

Maintenance of human body temperature is managed physiologically by a careful and precise balance of heat generation and loss known as thermoregulation. The body loses heat via a number of routes, including convection, conduction, radiation and evaporative cooling. When the surrounding air temperature is higher than body temperature, heat loss via convection can be impaired and heat will be gained from the environment to the skin; this will result in a raised core body temperature and the body will then initiate physiological responses, such as sweating, to aid in cooling. Sweating is the most effective mechanism for losing heat and maintaining body temperature, but excessive sweating can lead to dehydration and electrolyte imbalances, which can give rise to serious health consequences.

Electric fans have been available since the late 19^th century, and are in widespread use worldwide as a means of relief from heat. They don’t actually cool the air, but help to regulate human body temperature by assisting with physiological mechanisms, such as sweating, that promote heat loss. Used improperly, however, fans can have the opposite effect, causing heat gain rather than heat loss. It is important, therefore, to know about the potential benefits and harms of electric fans when choosing whether to use one.

There has been little comparative intervention research on the physiological effects of electric fans, and important gaps in knowledge exist about the use of fans, which might lead to their inappropriate use. A team of Cochrane researchers, therefore, set out to determine how the use of electric fans affects important health outcomes when they are used during heatwaves, in order to consolidate and help to develop the knowledge base for the public health impacts of heatwaves. They worked together over less than nine months to produce this up-to-date summary of existing research, which is part of the portfolio of reviews in Evidence Aid, a project to provide evidence for people involved in disaster risk reduction, planning, response and recovery.

The resulting Cochrane Review is the first to assess an intervention for alleviating the effects of environmental heat. Unfortunately, the researchers were unable to identify any eligible studies, despite extensive searching, including a special focus on the Indian and Chinese literature, and correspondence with several experts in this topic area. As a result, the review cannot not draw any definite conclusions about the health effects of electric fans during heatwaves, but articulates the need for high quality research to resolve the longstanding and ongoing uncertainty about the benefits and harms of electric fans as a health intervention. It concludes with the outline for a randomised trial which would be an important step in the right direction of helping people make well-informed choices.