Disclaimer

What These Estimates Cannot Account For

Real-world UV exposure and individual response are influenced by many factors that this tool does not and cannot model:

• ☁️ Cloud cover and aerosols: Clouds reduce UV by 10–90% depending on type and thickness. The UV Index forecast may be based on clear-sky conditions that do not reflect real-time attenuation. Always check the actual sky conditions.
• 🌲 Shade: Trees, buildings, umbrellas, and other structures provide variable UV reduction. Moving in and out of shade changes your dose in ways the timer cannot track.
• ⛰️ Altitude: UV radiation increases approximately 10–12% per 1,000 m (3,280 ft) of elevation. At high altitude, actual burn risk is substantially higher than calculated.
• 💧 Reflection from water, snow, and sand: Water reflects 10–30% of UV; dry sand ~10–15%; fresh snow 80–85%. Near highly reflective surfaces, effective UV dose is significantly increased.
• 🧴 Sunscreen: Proper application of SPF 30 sunscreen reduces effective UV by ~97%; SPF 50 by ~98%. However, most people apply far less than the standard test amount, substantially reducing real-world SPF protection. The calculator does not model sunscreen application.
• 💊 Medications and photosensitivity: Many medications increase UV sensitivity, including tetracyclines, fluoroquinolones, thiazide diuretics, retinoids, certain NSAIDs, antihistamines, and many others. If you take any medication, consult your pharmacist or physician about photosensitivity risk before extended sun exposure.
• 🌙 Prior tanning: Accumulated sun exposure in the days and weeks before an outing increases your effective MED. The calculator uses baseline, untanned MED values.
• 🧬 Individual biology: Age (older adults burn faster, synthesize vitamin D less efficiently), genetics, skin conditions, immunosuppression, post-radiation skin, and many other factors alter individual UV responses.
• 🌍 Season and latitude: In winter at high latitudes, UVB may be too low for meaningful vitamin D synthesis regardless of UV Index readings, which can be elevated by UVA alone.
• 🌡️ Temperature: Temperature is displayed for context only. High temperature does not mean high UV. Cold, high-altitude days can have extreme UV. Hot, hazy days can have moderate UV.

Accuracy of Estimates

The burn time and vitamin D estimates in SunSafe Timer are derived from reference MED tables and Holick's simplified linear vitamin D rule. These are well-established educational frameworks used in public health communication, but they carry substantial uncertainty:

• • MED values represent population medians — individual MED can vary ±50% from the table values.
• • Vitamin D estimates are order-of-magnitude approximations; real photosynthesis varies by skin type, wavelength distribution, body temperature, and many other factors.
• • UV Index forecasts from weather APIs may lag real-time conditions by minutes to hours.
• • The app uses current UV Index — intraday UV change is not automatically tracked by the timer.

Seek Professional Advice

If you have a personal or family history of skin cancer, photosensitivity disorders, albinism, or xeroderma pigmentosum, or if you are immunosuppressed, please consult a board-certified dermatologist before spending extended time in the sun.

For vitamin D deficiency, supplementation guidance, or skin disease management, consult a licensed physician.

Data Privacy

SunSafe Timer does not collect personally identifiable information. An anonymous session token is stored in your browser session cookie to save your preferences and optional exposure history. Location data (latitude and longitude) is used only to fetch weather data and is not permanently stored or associated with any personal identity. Exposure logs, if saved, are associated only with your anonymous session token.

No Warranty

This software is provided "as is" without warranty of any kind, express or implied. The authors disclaim all liability for any damage, injury, health consequence, or other harm arising from use of or reliance on the information provided by SunSafe Timer. Use at your own risk.