WCAG Master Guide: Seizure and Physical Reactions

According to WHO, around 5 million people are diagnosed with epilepsy every year.

This neurological condition is deemed a disability when it greatly affects someone’s ability to do everyday activities over an extended period of time. 

The Website Content Accessibility Guidelines (WCAG) include requirements for web users who struggle with seizures and they need to be considered when remediating your website.

Neurological Disabilities and Accessibility

Users with neurological conditions such as epilepsy can generally enjoy a smooth browsing experience.

However, flashing or flickering content can be dangerous for someone with photosensitivity.

When we view certain types of content, light patterns synchronize cells within the visual cortex. If these neurons work together too quickly though, they recruit additional neurons into a hyper-synchronous discharge, which causes a seizure.

WCAG requires business owners and developers to be cognizant of users with neurological conditions when developing websites and content to ensure they are not negatively affected. 

WCAG Seizure and Physical Reactions Success Criteria

Here are the success criteria you would need to meet in order to achieve Level A or higher.

Three Flashes or Below Threshold

A web page should not house any content that flashes more than three times in a one-second period. A flash should also be below the general flash and red flash thresholds. 

A general flash is defined as a pair of opposing changes in relative luminance of 10% or more of the maximum relative luminance (1.0).

A red flash is defined as any pair of opposing transitions that include a saturated red color.

Content is below the necessary thresholds if:

• There are no more than three general flashes and/or no more than three red flashes within a one-second period.

• Flashes occurring concurrently do not occupy more than a total of .006 steradians within any 10-degree visual field on the screen at a typical viewing distance.

The only exception to this requirement is if the flashing is a fine, balanced pattern such as white noise or an alternating checkerboard pattern.

This requirement ensures that users with seizures are not impacted. 

Animation from Interactions

If a motion animation is triggered by an interaction on a website, a user should have the ability to disable it. This is only true if the animation is essential to on-site functionality or the information being conveyed. 

This ensures that users are not harmed or distracted by motion, which can often cause dizziness, nausea, and headaches.

Flashing Content Best Practices

Being mindful of the effects of flashing content is key to WCAG compliance. Here are a few best practices to keep in mind: 

Avoid flashing content wherever possible. If flashing images, videos, and GIFs are not essential to a webpage, they should rather be avoided.

Provide a warning. If a video or motion animation contains flashing imagery, a user should be warned so that they can steer clear of the content. 

Offer more control. Motion animations that are essential to the information on your site should come with pause and stop controls to ensure users don’t need to interact with them if it doesn’t suit them. 

Frequently Asked Questions