How can you identify apps that are ‘spying’ your iPhone?

I found an old question about "How can one identify which app is ‘spying’ on you and how to prevent it from doing so?" I wonder if it is possible. Because when I read such articles that it may be impossible to detect such apps it makes me crazy. I do not want anyone to read my messages or look at my p[personal information.

[Edited by Moderator]