Photosensitivity refers to a condition in which an individual exhibits abnormal sensitivity or reaction to light. People with photosensitivity may experience symptoms such as eye discomfort, headaches, skin reactions, or seizures when exposed to certain light sources, including natural sunlight or artificial light. Photosensitivity can be triggered by specific wavelengths or intensities of light, such as bright or flickering light. For example, striped or high-contrast patterns may induce discomfort or visual confusion or disturbances.
Understanding photosensitivity is essential for creating usable environments and products that minimize potential adverse effects and promote the well-being of individuals who are susceptible to this condition.
Photosensitivity can have various underlying causes, ranging from medical conditions to genetic predispositions. Some common causes include:
Certain genetic conditions, such as xeroderma pigmentosum and porphyria, can result in heightened sensitivity to light. These conditions affect the body's ability to repair DNA damage or produce certain enzymes, making individuals more susceptible to light-induced reactions. Inherited retinal disorders such as Retinitis pigmentosa result in adverse reactions to bright light, whether reflected or emitted.
Medications and treatments
Some medications, such as certain antibiotics, antihistamines, or nonsteroidal anti-inflammatory drugs (NSAIDs), can increase photosensitivity as a side effect. Additionally, certain medical treatments like chemotherapy or radiation therapy may render the skin more sensitive to light.
Certain skin conditions, such as eczema, lupus, or dermatitis, can make the skin more sensitive to light exposure. In these cases, exposure to sunlight or other sources of light can trigger skin rashes or other adverse reactions.
Common photosensitivity symptoms may include:
Individuals with photosensitivity may experience eye strain, eye pain, redness, reduced acuity, reduced contrast sensitivity, or excessive tearing when exposed to bright or intense light.
Exposure to sunlight or artificial light sources may cause skin rashes, redness, itching, or blistering in individuals with photosensitivity. These reactions are often localized to exposed areas of the skin.
Headaches and migraines
Some people with photosensitivity may experience headaches or migraines triggered by light exposure, especially in cases of bright or flickering light sources.
Managing photosensitivity involves both preventive measures and treatment options. Here are some common approaches:
In certain cases, medications such as topical corticosteroids or antihistamines may be prescribed to alleviate symptoms or manage specific underlying conditions associated with photosensitivity.
Limiting exposure to bright or flickering lights can help prevent or minimize symptoms. This may involve controlling with blinds or shades and/or adjusting the lighting in indoor environments, using window coverings, or wearing a hat with a wide brim and/or tinted lenses.
Wearing protective clothing, such as long-sleeved shirts, wide-brimmed hats, and sunglasses with UV protection, can shield the skin and eyes from harmful ultraviolet (UV) rays.
Applying broad-spectrum sunscreen with a high sun protection factor (SPF) is crucial to protect the skin from UV radiation. It is recommended to use sunscreen with both UVA and UVB protection.
Photosensitivity and web accessibility
Photosensitivity can limit an individual’s ability to properly access websites and web-based content. This is especially true when web-based content contains elements that can trigger photosensitive reactions. These elements can include flashing or flickering animations, rapid image sequences, auto-playing videos, bright white or light color schemes, and high-contrast, geometric patterns. When these elements are present, an individual with photosensitivity may experience discomfort, reduced acuity, disorientation, seizures, or other neurological symptoms.
To prevent these reactions, website owners, developers, and designers should adhere to web accessibility best practices and standards, such as the Website Content Accessibility Guidelines (WCAG). These guidelines are referenced in many anti-discriminatory legislation, including the Americans with Disabilities Act (ADA), the Accessibility for Ontarians with Disabilities Act (AODA), and Section 508 of the Rehabilitation Act, as the standards that websites and web-based content should conform to.
What sections of WCAG apply to photosensitivity?
The Web Content Accessibility Guidelines (WCAG) include several instructions that directly apply to photosensitivity, including:
- Websites and web-based applications (e.g., PDFs) should not feature content that flashes more than three times in one second
- Permissible flashes must be below the general flash and red flash thresholds
- Moving, blinking, or scrolling content can be paused, stopped, or hidden by the user
Designing websites and web-based applications with photosensitivity in mind
To create digital environments that are welcoming to people with photosensitivity, the following best practices can be followed:
- Avoiding excessive use of flashing or rapidly changing content: One should minimize the use of animations, blinking elements, or rapidly changing visuals that can induce seizures. If animations are necessary, they should be subtle and moderately paced
- Providing clear warnings for potentially triggering content: If your website contains content that may include flashing or rapidly changing visuals, such as videos or interactive elements, clear warnings or alerts should be provided before users encounter them
- Using a consistent and simple design: A clean and consistent design with user controls helps reduce cognitive load and provides a more predictable browsing experience. Cluttered layouts, excessive visual distractions, and erratic color schemes should be avoided
- Offering user controls to manage visual elements: Website visitors should be provided with options to control or adjust visual elements. For example, options to pause or stop animations, hide moving or blinking content, adjust the overall speed of animated components, change background and foreground to reduce brightness, and control glare, empower the individual users to customize their browsing experience according to their comfort level
- Designing with color contrast in mind: Ensuring sufficient color contrast between text and background enhances readability
- Optimizing page loading and performance: Slow-loading pages or sudden visual changes during page transitions can be disorienting for individuals with photosensitivity. Website performance should be optimized to provide smooth and predictable browsing experiences, minimizing sudden visual disruptions
- Providing accessible alternatives: Whenever possible, accessible alternatives should be included for visual content. This can include text descriptions for images using alt text, captions for videos, or transcripts for audio content. These alternatives assist people with photosensitivity and improve overall accessibility for individuals with other disabilities
- Conducting user testing and gathering feedback: People with photosensitivity should ideally be involved during the design and testing phase. Their feedback and insights should be gathered to identify potential triggers or areas of improvement. User testing provides valuable insights into how website design may affect individuals with photosensitivity