Don't understand how Blockchain can protect privacy for personal data

Hi!

I know how public Blockchains work under the hood but I don't really understand one of its use cases: privacy for healthcare data.

We can read a lot of about public Blockchains being able to provide privacy to individuals, especially regarding healthcare data. I don't really understand this argument because we all know that data stored on a public Blockchain are public and can be read by anyone.

How can this guarantee privacy? It could if we don't store the actual private data but a hash of it, for example. But I'm not sure this is how it is supposed to work.

​

Does anyone know how this could work? Or can anyone describe the data workflow at a high-level view (what is currently stored on the Blockchain? By whom? How is it read by other people/companies/organizations? etc.)?

​

Thanks!