How to check what an app can see, and change it.
Every so often an app asks for something, and the prompt is written so the answer feels obvious. That is a good moment to slow down. On iOS, health permissions are more precise than most people realise, and every one of them can be changed afterwards.
What the permission actually is
Health access is not one switch. Apps are granted access separately for reading and for writing, and separately for each type of health data. An app can be allowed to write workouts without ever being able to read your sleep.
Two consequences are worth carrying with you. An app allowed to write a data type can also read the data it wrote. An app allowed to read a data type can read what every other source wrote into it, not only its own records.
What you can check before you install anything
An app's App Store page carries privacy information the developer has to supply: the types of data the app may collect, and whether that data is linked to you or used to track you. Reading it takes about twenty seconds and it is the cheapest check available.
Apple also requires any app that touches Health data to give people a privacy policy detailing its use of that data, and health data may not be used for advertising. A policy that is hard to find, or vague about what leaves your phone, is itself an answer.
See what you have already granted
- Open the Health app.
- Tap Summary, then tap your picture or initials at the top right.
- Below Privacy, tap Apps or Devices. The screen lists everything that has requested access.
- Tap an item, then turn permission to write data to, or read data from, Health on or off.
To look at it the other way round, by data type rather than by app, open the health categories, tap the category you care about, then below Options tap Data Sources & Access.
There is a wider view too. In the Settings app, go to Privacy & Security, then App Privacy Report. It shows how apps are using the permissions you granted them, and their network activity.
What turning it off does, and what it does not
Revoking read access does not announce itself to the app. Its queries simply return nothing, the same response an empty database would give. That is deliberate. It stops an app working out your health status from the types of data you do and do not track.
Turning access off also does not remove data an app has already written into Health. That stays until you delete it. To delete it, open the category, tap Show All Data below Options, then swipe left on a record and tap Delete. To clear a whole data type, tap Edit, then Delete All.
Deleting is permanent, so if there is any chance you will want that history later, take an export first.
On consent prompts in general
If a prompt asks you to agree to something and tells you what happens if you decline, the useful move is to find the same claim written down somewhere the company is accountable for it: the privacy policy, the terms, or a published help article.
A prompt is a piece of interface design and it can be rewritten next week. A policy is a commitment. When the two do not say the same thing, that gap is the thing to ask about before you agree to anything.
Steps verified against Apple's iPhone User Guide (iOS 26) and the Apple Platform Security guide, July 2026. Apple changes its interface from time to time, so if a screen does not match, the wording here is what Apple documented at the time of writing.