Apple Health

Settings → Your data → Apple Health. One switch, Save my entries to Apple Health, and one button, Import from Apple Health. Both are off or untouched until you use them, and permission can be withdrawn at any time in the Health app.

Reading

Fills in history you already have — see bring your history with you. Two things are read, and nothing else:

• Periods and symptoms, when you tap Import from Apple Health. What will be added is shown before anything is written.
• Your medication list, read only, so you do not retype the names.

Weight, steps, sleep and temperature are not read. There is no weight in this app at all, and sleep stays a word you wrote here.

Writing

Only the facts you entered yourself: period days, spotting, and these symptoms — acne, hair thinning, bloating, fatigue, abdominal cramps, pelvic pain, lower back pain, headache, mood changes.

Never anything the app worked out for you. Never a date you marked approximate.

Deleting

Apple Health is left alone. Deleting everything in Cycle Ally clears the phone's own copy and does not touch what was written to Health — the delete screen says so. Samples there, whoever wrote them, you remove in the Health app.

If you never turn it on

Nothing changes. Every feature works without Apple Health; the integration only saves typing and keeps your records together.