Robert Bartholomew Ph.D.

It's Catching

A Popular Website Is Reportedly Making People Sick

Can a website make you unwell?

Posted Jul 06, 2020

Epilepsy is a neurological disorder of the central nervous system whereby abnormal brain activity results in seizures, unusual behaviors, sensations, and varying states of awareness. Photosensitive epilepsy (PSE) is a less common form of the condition where seizures are caused by a variety of visual stimuli such as flashing lights and sharply contrasting geometric patterns.

Epilepsy is more common as people age, whereas PSE is more common in children and rare in adults. The Centers for Disease Control reports that there are about 3 million American adults and 470,000 children with active epilepsy (CDC 2017). About 1 in 100 people have been diagnosed with the condition. Of these, about 3 percent have PSE, with the most common trigger being flashing lights at a rate of between 5 to 30 per second in addition to “certain visual patterns” (Epilepsy Foundation, 2019). PSE occurs at a rate of about 1 in 4,000 in the general population, although the incidence rate in any given year is estimated to be 1.1 per 100,000 is a household name for many in the knitting and crochet community. Founded in 2007, the Boston-based company has grown to become a popular social networking site for people who engage in fiber arts. In March 2020, they reported just under 9 million registered users. The company made international headlines in 2019 for banning pro-Trump posts (Horton, 2019; Covery 2019).

Then, on June 16, 2020, the operators of Ravelry unveiled their new website design. Soon after the new design went live, a user complained that the site was responsible for migraine headaches. This was followed by an Instagram post: “Warning: Ravelry may potentially trigger seizures for people with photosensitive epilepsy as well as migraines. Viewer discretion is advised.” Before long, visitors began reporting a long list of health complaints that they attributed to viewing the site. In addition to headaches and seizures, users were complaining of dizziness, nausea, visual disturbances, eye pain, vertigo, fatigue, difficulty concentrating, confusion, numbness, muscle spasms, anxiety, depression—even vomiting. One woman wrote: “Within minutes of seeing the new design I had searing pain in my eyes and head, and trouble focusing my vision. It lasted hours.” Another wrote that after logging off, within 10 minutes “the room started rolling and it was like I was on a boat with all the queasiness and motion sickness.” She had a history of migraines. Another complained that she was “not able to use the website without pain.”

Here’s the problem: It appears to be an ordinary website. There are no flashing lights or obvious features that should cause health issues. That a small number of people self-report having a seizure does not prove that it was triggered by the site. Some claim that the health effect is delayed by hours or days after viewing the site. PSE is rare but it’s common enough that out of such a large population of users on any given day, you would expect some to be experiencing a variety of health complaints. Some users say that just viewing a link to the website or a screenshot of the site is making them unwell. And some visitors say they have fallen ill immediately upon looking at the site.

There is no further evidence to support the claims that Ravelry itself is making people sick or that it is anything other than a normal website. Given that, the most likely explanation for these reports of illness may be mass suggestion and the redefinition of various ailments as Ravelry-related. New technologies have often been blamed for health problems, from the telephone to Wi-Fi to mobile phones and 5G. Belief and expectation have a powerful impact on our health. Double-blind studies have shown that subjects who report symptoms after exposure to electromagnetic fields cannot detect the presence of those fields, while sham exposure to electromagnetic fields results in symptoms as frequently as real exposure (Rubin et al., 2005, 2006). Studies that assess expectations prior to being exposed to sham or real electromagnetic fields suggest that the person’s expectations play a key role in determining whether symptoms develop or not. If people expect to have symptoms, they are much more likely to have them.

Perhaps the most famous case of mass psychogenic illness masquerading as PSE occurred in Japan on December 16, 1997, when over 12,000 Japanese children reported an array of symptoms after watching a TV episode of the animated show Pokémon. During the program, a Pokémon engaged in a thunderbolt attack that included rapidly flashing stroke lights. PSE was diagnosed in a minuscule fraction of those affected—nearly all children—while the remainder exhibited symptoms consistent with mass psychogenic illness. Dramatic news reports of the small number of cases were deemed to have elicited high levels of anxiety in children who had watched the episode after they and their parents feared that they, too, had been made unwell (Radford and Bartholomew, 2001).


Convery, Stephanie (2019). “’White supremacy': popular knitting website Ravelry bans support for Trump." The Guardian, June 24.

da Silva, A. Martins, Leal, Bárbara (2017). “Photosensitivity and epilepsy: Current concepts and perspectives—A narrative review.” Seizure: European Journal of Epilepsy, Volume 50, pp. 209-218 (August 1). DOI:

Horton, Alex (2019). “Ravelry, the Facebook of knitting, has banned pro-Trump posts over ‘open white supremacy.” Washington Post, June 24.

“Photosensitivity and Seizures.” Epilepsy Foundation, Landover, Maryland, September 30, 2019. Accessed at:,trigger%20a%20seizure%20is%20small.

Radford, Benjamin, Bartholomew, Robert E. (2001). “Photosensitive Epilepsy or Mass Psychogenic Illness?” The Southern Medical Journal 94(2):197-204.

Rubin. G.J., Munshi, D., Wessely, S. Electromagnetic hypersensitivity: a systematic review of provocation studies. Psychosomatic Medicine 2005;67(2):224–32.

Rubin, G.J., Everitt, B.S., Wessely, S. Are some people sensitive to mobile phone signals? Within participants double-blind randomized provocation study. British Medical Journal 2006;332(7546):886–91.

Zack MM, Kobau R. National and State Estimates of the Numbers of Adults and Children with Active Epilepsy — United States, 2015. Morbidity and Mortality Weekly Report 2017;66:821–825. DOI: (Centers for Disease Control).