Part of Heathrow Airport's Terminal 4 was evacuated on Monday after 21 people fell ill, prompting a hazardous materials alert. However, police found no trace of any adverse substance after a thorough search.
A Metropolitan Police source suggested the incident could be a case of mass hysteria, and some experts agree. Dr Robert Bartholomew, a sociologist at the University of Auckland, said it was 'almost certainly an episode of mass psychogenic illness that is anxiety-based'.
Mass psychogenic illness, formerly known as mass hysteria, can be triggered by the sudden perception of a toxic agent, such as an unfamiliar smell. Symptoms include headache, dizziness, and fainting, with victims often recovering quickly. Bartholomew noted that such episodes tend to come out of the blue.
If confirmed, this would not be the first airport-related case. Bartholomew investigated a similar event at Melbourne airport in 2005 when 57 people fell ill after reporting a 'gassy smell'. A 2010 study of UK chemical incidents found that 19 out of 280 reports were probable cases of mass psychogenic illness.
Prof Sir Simon Wessely of King's College London cautioned that it was 'a bit early' to judge the Heathrow event, but added that if investigations rule out other causes, it could be an episode of mass sociogenic illness. Bartholomew stressed that the condition is not a mental disorder and that victims experience real symptoms.
