KNOW YOUR SUN. OWN YOUR DOSE.
How it works
The dose engine: actual exposure, not a forecast.
Your Watch already knows how long you've been outside. ARPANSA already knows how strong the UV is right now. UVDose is the layer that fuses the two, on-device, into a personal Standard Erythemal Dose (SED) ledger, the same clinical unit your doctor already understands.
The core loop
Three parts, one on-device engine.
Apple Watch
The ambient light sensor passively measures Time in Daylight and writes it to HealthKit. No action needed, works in the background on SE 2nd gen, Series 6+, and Ultra.
UVDose dose engine
The iPhone app reads HealthKit daylight samples, pulls live UV from the nearest ARPANSA station (or Open-Meteo forecast fallback), and computes your personal SED accumulation, entirely on-device.
Nudges + ledger
Proactive prompts to apply, reapply, or seek shade, plus a longitudinal dose ledger: daily dose, weekly trend, burn log, and a risk profile against your skin type.
The science, in plain English
What's an SED, and why should you care?
Standard Erythemal Dose. It sounds clinical, but it's the simplest number in the app: a running tally of how close you are to burning, built from the sun you're actually in, not a forecast.
What it measures
A fuel gauge for sun damage
1 SED is roughly the dose of UV that causes the first faint reddening on fair skin, the scientific starting point for sunburn. It's the same unit dermatologists already use, not a score UVDose made up.
Why it matters
Better than "it doesn't feel that hot"
Heat, time outside, and cloud cover are all poor proxies for UV damage. SED tracks the one thing that actually causes burns: erythemally weighted UV energy, accumulated minute by minute, whether you notice it or not.
Why it's personal
Everyone's 1 SED feels different
Your safe dose isn't a fixed number. It's set by your skin type: fair skin might reach its threshold around 2 SED, while deeply pigmented skin can safely absorb 10+ SED first. A sun app that ignores skin type is just guessing.
How UVDose calculates yours
Set once, tracked automatically
Pick your skin type once during onboarding. From there, your Watch's daylight time and the live UV index at your location combine into SED in the background, so UVDose can nudge you before you burn, not after.
The moat
Standard Erythemal Dose: the same unit your doctor uses.
1 SED = 100 J/m² of erythemally weighted UV. Every interval of exposure is weighted by live UV, actual daylight time, and your personal burn threshold, not a generic "burn time" guess.
UV_index(t, location)
ARPANSA live, 13 stations
Real-time readings from Australia's national UV monitoring network, interpolated by location, updated minute by minute. Open-Meteo UV forecast fills the gaps for non-station locations and overseas travel, always labelled in the UI.
daylight_fraction(t)
HealthKit Time in Daylight
15-minute daylight samples from your Watch's ambient light sensor. Daylight is a presence proxy only: UV magnitude always comes from ARPANSA, never inferred from brightness alone.
MED(fitzpatrick_type)
Your personal burn threshold
Minimal Erythemal Dose by Fitzpatrick skin type I–VI (type I ≈ 2 SED, type VI ≈ 10+ SED), captured once in onboarding via a skin-type selector, and recalibrated automatically after a logged sunburn.
sunscreen_modifier
SPF-adjusted decay curve
Log sunscreen with one tap (phone, Watch app, or notification action). Protection decays over roughly two hours, accelerated by swimming or sweat detected from HealthKit workouts.
Nudges
Configurable alerts, not nagging.
SPF-reminder threshold (50–90%, default 70%), device choice, reapplication interval, quiet hours, and per-category toggles all live in Settings. Threshold alerts fire once per crossing and escalate only if you keep accumulating dose 30+ minutes after the alert.
| Trigger | Notification |
|---|---|
| 15+ min daylight detected & UV ≥ 3 & no sunscreen logged | "You're outside and UV is High (7). Slop on sunscreen, tap when done." |
| Sunscreen logged 2h ago & still accumulating daylight | "Time to reapply, protection has worn off." |
| Risk ratio reaches your alert level (default 70%, adjustable 50–90%) | "You're at 70% of your safe dose today. Apply SPF 50+ now, or head for shade." Sent to iPhone and/or Watch; tap to log application directly from the alert. |
| Every morning at 8am, your local time | Morning brief: "UV hits 3 at 9:20am today. Peak 11 at 1pm." |
On the wrist
Log without touching your phone.
Analytics & risk profile
A longitudinal record, not just a daily number.
Today ring
Dose vs. threshold
An instantly legible Apple-ring-style view of today's dose against your personal burn threshold.
Heatmap
Weekly & monthly trend
Dose by day, with over-threshold days flagged at a glance.
Burn log
Recalibrating threshold
Log a sunburn event and UVDose recalibrates your personal threshold from what actually happened.
Lifetime ledger
Exportable PDF
Twelve months of exposure history, ready to email your GP or dermatologist before a skin check.
Risk score
Educational, not diagnostic
A composite of skin type, cumulative dose, burn frequency, family history flag, and geography, framed as education, never as a cancer-risk diagnosis.
Mole Monitor
Self-checks, not just reminders
Guided macro photos on a 3 or 6 month cycle, with side-by-side comparison. Full detail below.
Mole Monitor
Requested by our clinic partner. It also solves the winter problem.
Every other feature on this page depends on UV season. Mole Monitor doesn't: photo cycles run year-round, which is exactly why it's now the primary answer to keeping UVDose useful through a Melbourne July.
Add a mole
Pick the spot on a simple body map, then take a close-up photo with an on-screen framing guide: a distance ring, lighting hints, and a ghost overlay of the last photo for alignment.
Get reminded
UVDose schedules a re-photo at your chosen interval, 3 or 6 months, matching the cycle our clinic partner recommends clinically.
Compare
Side-by-side and flick-to-compare views help you spot change between visits. Every photo stays on-device with the rest of your ledger.
Flag and act
Mark a mole as "looks changed" and UVDose prompts you to book a skin check, aware of your partner clinic if you have one.
Monitoring is free for your first 2 moles. Plus unlocks unlimited moles and comparison tools, see pricing.
See it in your pocket
Ready to see what your own dose ledger looks like?
Download UVDose from the App Store and start your ledger today.