Sources

References for the medical, UV, and skin-sensitivity information shown inside Stay Cool. Last updated June 2026.

Not medical advice. Stay Cool surfaces general-population sun-safety guidance from peer-reviewed and public-health sources. It is not a substitute for personalized medical advice from a licensed dermatologist or your physician. For sun-sensitive medical conditions (lupus, melanoma history, photosensitizing medications), consult your doctor.

Fitzpatrick skin sensitivity scale (Types I–VI)

The six-type skin sensitivity scale used in the Profile screen is the Fitzpatrick scale, a standard dermatology classification for skin response to ultraviolet radiation.

Fitzpatrick TB. The validity and practicality of sun-reactive skin types I through VI. Archives of Dermatology. 1988;124(6):869–871. PubMed 3377516.
American Academy of Dermatology Association. How to choose a sunscreen. aad.org · sun protection.
U.S. Food & Drug Administration. Sun protection factor (SPF). fda.gov · sunscreen guidance.

We use the scale to set a default UV-alert threshold per skin type. The thresholds Stay Cool uses (Type I ≈ UV 3, Type VI ≈ UV 10) are conservative estimates derived from the AAD guidance above. Your dermatologist may recommend different thresholds for your skin.

Sunscreen reapplication every 2 hours

The recommendation to reapply broad-spectrum sunscreen every two hours of UV exposure is the standard guidance from major dermatology and public-health bodies.

American Academy of Dermatology Association. Sunscreen FAQs. aad.org · sunscreen FAQs.
Centers for Disease Control and Prevention. Sun safety. cdc.gov · sun safety.
World Health Organization. Radiation: The ultraviolet (UV) index. who.int · UV index.

Reapplication is also recommended after swimming, heavy sweating, or towel drying, regardless of how much time has passed.

Sun-sensitive conditions and medications

Stay Cool’s “Sun-sensitive mode” halves the default daily UV exposure threshold. It exists for people whose baseline tolerance to UV is reduced by a medical condition or medication. The categories named in the toggle (lupus, melanoma history, photosensitizing medications) come from these dermatology and pharmacology references.

Lupus Foundation of America. How sun exposure can trigger lupus symptoms. lupus.org · sun & light.
American Academy of Dermatology Association. Melanoma: signs and symptoms. aad.org · melanoma.
Skin Cancer Foundation. Photosensitizing medications. skincancer.org · photosensitivity.
DermNet NZ. Photosensitivity — drug-induced photosensitivity. dermnetnz.org.

If any of these apply to you, talk to your doctor. Stay Cool’s halved threshold is a conservative default, not a clinical recommendation.

UV index thresholds and shade-seeking guidance

The default UV thresholds Stay Cool uses to recommend shade, sunscreen reapplication, or staying indoors come from the World Health Organization’s global UV Index standard.

World Health Organization, World Meteorological Organization, UNEP, ICNIRP. Global Solar UV Index: A Practical Guide. who.int · UV Index guide.
U.S. Environmental Protection Agency. UV Index Scale. epa.gov · UV index scale.

Shade calculation methodology (non-medical)

The shade-percentage scores Stay Cool shows on routes are calculated from OpenStreetMap building footprints, SunCalc solar position, and Open-Meteo cloud-cover forecasts. These are estimates, not measurements. See our Terms of Service for the full accuracy disclosure.

Questions

Questions about a specific claim or a missing citation? Email support@walkintheshade.com and we will respond with the source we relied on. If a claim is wrong, we want to fix it.