Do all babies go through stranger anxiety?

Yes: I look at it as a great indicator that they can think which is more important to me than their first steps. They realize strangers are not as predictable or nurturing as their primary caregivers.This comes in at a time when they have not developed the idea of "permanence" or that you can exist in the next room if you are not in their sight, so they also fuss if you try to leave. It will pass.

Degree of anxiety: varies, but neurotypical 5- mo.-olds have implicit memory. Remembering what happened yesterday, leads to recognition of stranger vs. non-stranger at 6 mos. I'd screen for Autistic Spectrum Disorder if a 6-9 mo.-old allowed strangers to pick him up without protest, had diminished eye-to-face gaze , did not raise his arms to be picked up, did not babble in a string ..ba-ba-ba...reciprocally.