About Sunwise
Sunwise publishes sun-safety guidance, which is health information — so it's reasonable to want to know who is behind it, where the numbers come from, and how far to trust them. This page answers all three: who builds the app, which data source supplies every UV reading, how the personal burn time is actually calculated, which standards and health authorities the guides draw on, and — just as importantly — what this site is not qualified to tell you.
Who makes Sunwise
Sunwise is built and published by App Deco Studio Inc., an independent software studio based in New Brunswick, Canada. It is a small, self-funded operation rather than a health organisation, a research group, or a venture-backed company, and Sunwise is its own product rather than a white-label of someone else's UV service.
Sunwise is free on the App Store, with an optional subscription handled by Apple. The app collects no personal information, stores your skin type on your own device and in your personal iCloud account, and never sends your precise location to a Sunwise server — the full detail is in the privacy policy.
Not affiliated with EPA's SunWise or UV Index: SunWise
This comes up often enough to state plainly: Sunwise has no relationship with SunWise, the U.S. Environmental Protection Agency's UV index programme and app. The names are similar and both concern UV, but they are unrelated products from unrelated publishers. EPA's SunWise is a government reference tool for US ZIP-code forecasts and sun-safety education; Sunwise is an independent Canadian app built around a personal burn time. The UV app comparison covers both side by side.
The same goes for UV Index: SunWise, a separate App Store app from a different developer that often appears near the top of App Store searches for “UV index app”. If you're looking for this app, its App Store name is Sunwise: UV Index & Sunburn, published by App Deco Studio Inc. Anything else with a similar name isn't ours, and we can't answer questions about it.
Where the numbers come from
Sunwise does not run its own weather model or operate UV sensors. Every figure in the app and the guides traces back to one of the following.
| Source | What it supplies | Why this one |
|---|---|---|
| Apple WeatherKit | Every UV index number in the app | Multi-model ensemble that accounts for forecast cloud cover, ozone, and your device's GPS altitude. It's the same source behind Apple's own Weather app, so the raw UV figure in Sunwise matches what iOS shows. |
| WHO / WMO / UNEP / ICNIRP | The UV index scale and its 0–11+ banding | The Global Solar UV Index is a jointly standardised measure, which is why a UV 7 means the same thing in Sydney as in California. The protection thresholds quoted in the guides (act at UV 3, take active measures at UV 8) come from this guidance. |
| The Fitzpatrick scale | Skin type input and the burn-time model | A dermatological phototype classification (Types I–VI) based on how skin burns and tans. It is the standard clinical shorthand for UV sensitivity and the reason a burn time can be personalised at all. |
| Standard erythemal dose (SED) literature | The burn-time arithmetic itself | 1 SED equals 100 J/m² of erythemally-weighted UV, and minimal erythemal dose (MED) by phototype runs from roughly 2 SED at Type I to about 10 SED at Type VI. That conversion is set out in full on the sun exposure tracker guide. |
| Public-health bodies | Guidance in the topic guides | Age-based advice draws on the American Academy of Pediatrics, Health Canada, the Canadian Dermatology Association, and Cancer Council Australia; US UV-index guidance draws on the EPA. These are cited in the guides where they apply. |
For why UV forecasts from different apps disagree by a point or two, and how to sanity-check a reading you don't trust, see the UV index accuracy guide.
How the burn time is calculated
There is no proprietary secret here, and the arithmetic is worth understanding because it tells you how much precision to read into the result. Sun exposure is a dose — intensity multiplied by time — measured in standard erythemal doses, where 1 SED is 100 joules per square metre of UV weighted for how strongly it reddens skin.
- •Rate — the UV index converts cleanly into dose: one hour of full exposure at UV 1 delivers roughly 0.9 SED, so an hour at UV 8 is about 7.2 SED.
- •Threshold — your minimal erythemal dose, the point at which skin starts to redden. It runs from roughly 2 SED for Fitzpatrick Type I to about 10 SED for Type VI.
- •Burn time — threshold divided by rate, recomputed as the UV index changes through the day. That is the whole model.
Two consequences follow, and both matter. Because burn time is inversely proportional to the UV index, doubling the UV halves your window. And because individual MED varies with tan, medication, and altitude, the output is a planning baseline for bare skin in open sun rather than a measurement of you specifically — which is why the app is deliberately conservative and why the guides recommend acting at roughly 60–70% of the number rather than at zero. The full derivation is set out in the sun exposure tracker guide.
How the guides are written — and what they aren't
The guides on this site are written in-house by App Deco Studio, drawing on the standards and public-health sources listed above, and revised as guidance or the app changes. Each carries a published and last-updated date so you can see how current it is.
The limits are worth stating directly rather than burying:
- •This is not medical advice. Nothing here is written or reviewed by a clinician, and we don't claim otherwise. For anything concerning your own skin — a persistent lesion, a photosensitising prescription, a diagnosed condition — talk to a doctor or dermatologist, who can account for facts about you that a forecast cannot.
- •Burn times and SED tables are estimates. They are derived from published phototype thresholds, not measured on you. Treat them as a planning baseline with a safety margin, not a guarantee.
- •Competitor comparisons are our reading of public information. App Store listings and features change without notice. Where a rival app does something better than Sunwise, the comparison says so — skin-type personalisation, for instance, is no longer unique to Sunwise, and the roundup was updated to reflect that rather than quietly keep the claim.
- •We have a commercial interest. These guides exist partly to introduce people to Sunwise. We think that's compatible with being accurate — a guide that oversells the app is worse than useless once someone installs it — but you should read them knowing it.
If you find something on this site that is wrong, out of date, or misleading, we'd genuinely like to know. Email sunwise@appdeco.ca and we'll correct it.
What Sunwise deliberately doesn't do
Being clear about the boundaries saves people installing the wrong tool:
- •It doesn't log your exposure in the background or write to Apple Health. It forecasts forwards rather than recording backwards — pair it with Apple Watch's Time in Daylight if you want logged minutes.
- •It isn't a sunscreen reapplication timer. That's a genuinely separate job, covered in the reapplication guide.
- •It doesn't measure UV with a sensor. No phone can — the reading is a forecast for your location, which is why it assumes open sky and can't know you spent the last half hour under a tree.
- •It doesn't diagnose anything. It has no view on moles, rashes, or skin lesions.
Get in touch
Questions, corrections, bug reports, and feature requests all go to sunwise@appdeco.ca. For the legal detail, see the privacy policy and terms of service.
