Everything on the Ethereum blockchain is public.
Therefore you cannot obscure data. This is because each Ethereum node stores a copy of the entire blockchain, and so each node could theoretically inspect their copy to find whatever data you wanted to be obscured.
That doesn't mean you can't put sensitive data on the blockchain, you just have to encrypt it first.
Encrypt data with a public key
If you want to store sensitive user information on the blockchain you should encrypt the data with their public key. Only the user with their private key can decrypt it.
This can seem like more work then you have to do with more normal web application, but it's actually a benefit. If you assume your data can be accessed by an attacker, you will avoid many security pitfalls that cause these huge data breaches. Security by obscurity is not really security at all!