Strobe lights used at dance music festivals triple the risk of an epileptic seizure, a study has found.
Researchers have warned flashing lights can trigger a seizure even in people who have never had one before.
A lack of sleep and drugs could also play a role – both of which are commonplace at festivals, doctors said.
They added that festival organizers rarely give a warning to individuals susceptible to what is known as photosensitive epilepsy.
The findings come as millions of people in the Europe prepare to take on the festival season.
Experts from a medical centre in the Netherlands revealed a case study of a 20-year-old man who collapsed and had a seizure at an EDM concert.
He had experienced an uncomfortable ‘aura-like’ experience while watching strobe lights before having a seizure which lasted a few minutes.
The unidentified man denied consuming any alcohol, drugs or medication and had no previous history of seizures, it was reported in BMJ Open.
Researchers, led by Dr Newel Salet of the Department of Internal Medicine, went on to reveal study findings of 400,343 festival visitors.
All had attended one of 28 electronic dance music festivals across the country throughout 2015.
A total of 241,543 were exposed to strobe lights at night-time festivals, as opposed to day time festivals where less lighting was used.
Medical assistance was provided on 2,776 occasions, according to data from one company which provided services to all the festivals.
Strobe lighting more than tripled the risk of seizures, as 30 of the 39 cases of epileptic seizure happened at a night-time event.
Fewer than one-third of people having a seizure had used drugs. But the proportion of people who had used drugs in both groups of visitors, suggesting that this alone wasn’t responsible for the heightened seizure risk.
Ecstasy is the most commonly used recreational drug at dance music events, the researchers said.
They concluded: ‘Regardless of whether stroboscopic light effects are solely responsible or whether sleep deprivation and/or substance abuse also play a role, the appropriate interpretation is that large [electronic dance music]festivals, especially during night time, probably cause at least a number of people per event to suffer epileptic seizures.
‘We think, however, that our numbers are probably an underestimate of the total number of people who had epileptic seizures.’
Anyone can have a seizure but it doesn’t mean they have epilepsy. Seizures of any kind which are triggered by flashing lights come under photosensitive epilepsy.
Louise Cousins, a spokesperson for Epilepsy Action, said: ‘Heavy alcohol use and recreational drugs could cause a seizure in people with or without epilepsy.
‘Sleep deprivation can also trigger seizures in some people with epilepsy.
‘It is possible that someone could experience their first seizure as a result of exposure to strobe lighting.
‘Epilepsy isn’t usually diagnosed until a person has experienced more than one epileptic seizure, or a doctor thinks there is a high chance they could have more seizures.’
Around three in every 100 people with epilepsy have photosensitive epilepsy.
The researchers advise anyone with photosensitive epilepsy to either avoid such events or to take precautionary measures.
These include getting enough sleep and not taking drugs, not standing close to the stage, and leaving quickly if they experience any of the ‘aura’ effects.