unfortunatelly it would not be possible for me (or any medical provider) to blindly identify this "blister" based solely on your description. you would need to be examined first-hand by a medical professional.
can you identify this strange blister? . what is a small blister-like flat bubble on my shoulder that causes no pain and no itchiness? it may have gone down a bit during the three weeks it has been there. no spreading and no additional blisters found. first i have ever noticed in my 57 years.