Jack Dorsey, cofounder of Twitter (now X), has introduced a new app named Sun Day, which tracks ultraviolet (UV) exposure and vitamin D levels.

The app is currently available for testing through TestFlight on iOS, according to a post by Dorsey on X.

Sun Day monitors the UV index based on the user’s location and provides sunrise and sunset times.

The app estimates vitamin D production based on skin type and clothing, offering six skin tone options.

It also tracks moon phases and syncs with Apple Health for integrated wellness data.

Additionally, Sun Day’s code is open-source on GitHub, enabling developers to clone or modify the application.

This release follows Dorsey’s recent introduction of Bitchat, a messaging app that allows communication over short distances using Bluetooth without requiring internet or mobile networks.

🔗 Source: The Economic Times

🧠 Food for thought

1️⃣ UV tracking apps address a critical but underserved health need

Sun Day enters a digital health segment addressing a significant public health concern, as one in three cancer diagnoses is skin cancer, with cumulative UV damage being a key factor1.

While UV monitoring apps aren’t new, they’ve remained a relatively niche category despite WHO and CDC efforts to promote awareness of UV radiation risks.

These organizations have emphasized the importance of UV index tracking, with the WHO launching their own SunSmart Global UV app in 2022 to combat the more than 1.5 million global skin cancer cases diagnosed in 20202.

The CDC also maintains a national Sunlight & UV Tracking Program to identify high-exposure regions and support prevention efforts3.

Dorsey’s entrance into this space brings celebrity attention to a health issue that affects millions but has received less technological innovation than fitness or mental health tracking.

2️⃣ Information alone doesn’t change behavior, a persistent challenge for health apps