apply-reduced-motion

name	apply-reduced-motion
description	Use when adding animations, transitions, parallax effects, or auto-playing video to a UI — to respect users' motion sensitivity preferences and prevent content that could trigger seizures.
source	W3C WCAG 2.1 SC 2.3.1 Three Flashes (Level A), SC 2.3.3 Animation from Interactions (Level AAA); CSS prefers-reduced-motion media query; Vestibular Disorders Association guidelines
tags	["accessibility","wcag","a11y","reduced-motion","animation","seizures","vestibular","developer"]
related	["design-accessibility-standards","apply-accessible-color"]

Implement Reduced Motion

Respect prefers-reduced-motion to prevent animation-triggered vestibular episodes, and never flash content more than 3 times per second.

Why This Is Best Practice

Adopted by: prefers-reduced-motion is supported in all modern browsers (Chrome, Firefox, Safari, Edge) since 2019 and is natively supported by macOS, iOS, Windows, and Android OS-level settings. Apple, Google (Material Design), and Microsoft (Fluent Design) all include reduced motion as a required accessibility consideration in their design systems. WCAG 2.1 SC 2.3.1 (Level A) prohibits content that flashes more than 3 times per second — this is legally required under all major accessibility laws. Impact: 35% of people with migraine disorders report sensitivity to motion and flashing. The Vestibular Disorders Association estimates 35 million Americans experience vestibular dysfunction — animations can trigger vertigo, nausea, and disorientation. The 2006 Pokemon epilepsy incident (685 children hospitalized after a flashing scene) is the documented case that established the 3 Hz flash threshold in broadcasting and later WCAG. Why best: Motion that can't be turned off affects users persistently across every visit. prefers-reduced-motion provides a system-level user preference — one CSS media query respects it across all animations without requiring an in-app setting.

Sources: W3C WCAG 2.1 SC 2.3.1, 2.3.3 (2018); CSS prefers-reduced-motion MDN documentation; Vestibular Disorders Association; Apple HIG Accessibility (Motion)

Steps

Step 1: Respect prefers-reduced-motion in CSS

/* Default animations for users without preference */
.card {
  transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.spinner {
  animation: spin 1s linear infinite;
}

/* Override: remove or reduce motion when user prefers */
@media (prefers-reduced-motion: reduce) {
  .card {
    transition: none;
  }

  .spinner {
    animation-duration: 3s;   /* slow down rather than stop, if needed */
  }

  /* Catch-all for unidentified animations */
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

The catch-all rule at the bottom is a safety net. Prefer explicit per-component overrides so reduced-motion doesn't accidentally break loading states.

Step 2: Read the preference in JavaScript for programmatic animations

const prefersReducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)');

function animateElement(el) {
  if (prefersReducedMotion.matches) {
    // Skip animation — show final state immediately
    el.style.opacity = '1';
    el.style.transform = 'translateY(0)';
    return;
  }

  el.animate([
    { opacity: 0, transform: 'translateY(20px)' },
    { opacity: 1, transform: 'translateY(0)' }
  ], { duration: 300, fill: 'forwards' });
}

// React equivalent
const prefersReducedMotion = useMediaQuery('(prefers-reduced-motion: reduce)');

Step 3: Never flash content more than 3 times per second (WCAG 2.3.1)

The threshold: content that covers ≥25% of screen area and flashes more than 3 Hz can trigger photosensitive seizures.

// Wrong — 10 flashes per second
setInterval(() => toggleHighlight(), 100);

// Right — safe rate (max 3/sec = minimum 333ms interval)
setInterval(() => toggleHighlight(), 400);

// Better — avoid flashing entirely; use smooth transitions

Test with the Photosensitive Epilepsy Analysis Tool (PEAT) or Harding Test for video content before publishing.

Step 4: Pause, stop, or hide all auto-playing animated content

<!-- Auto-playing animation: always provide pause control -->
<video autoplay muted loop aria-label="Product feature demo">
  <source src="demo.mp4" type="video/mp4">
</video>
<button id="pause-btn" aria-controls="demo-video">Pause animation</button>

<script>
  const video = document.getElementById('demo-video');
  document.getElementById('pause-btn').addEventListener('click', () => {
    video.paused ? video.play() : video.pause();
  });
</script>

WCAG 2.2.2 (Level A) requires that any animation or video that auto-plays for more than 5 seconds has a mechanism to pause, stop, or hide it.

Step 5: Test by enabling reduced motion in OS settings

• macOS: System Settings → Accessibility → Display → Reduce Motion
• iOS: Settings → Accessibility → Motion → Reduce Motion
• Windows: Settings → Ease of Access → Display → Show animations in Windows (off)
• Android: Settings → Accessibility → Remove animations

Verify all animations are removed or reduced after enabling the OS preference.

When NOT to Use

• Animations that convey critical state (loading spinner, progress bar) — don't remove entirely; slow them down instead. A stopped spinner looks like a hang.
• Non-animated transitions — CSS color transitions without movement do not trigger vestibular symptoms. Short color transitions (< 200ms) are generally acceptable.

Common Mistakes

Checking prefers-reduced-motion only in CSS but not in JavaScript animations. GSAP, Three.js, Framer Motion, and canvas animations require a JavaScript check. CSS prefers-reduced-motion does not affect JavaScript-driven animations.

Removing all transitions but keeping scroll-jacking. Parallax scroll effects and scroll-jacking trigger vestibular symptoms even without CSS animations. Disable scroll-behavior: smooth and parallax under prefers-reduced-motion.

Assuming reduced motion means no motion. Some users prefer less motion, not zero motion. Subtle fade-in (opacity only, no position change) is generally acceptable. Test with actual users who have vestibular sensitivities.