Don't know if they get pourous but do get brittle or seems so to me . I have one of those Dr. hands bottle , the label had came clean off of it . I used Elmer's glue to put it back on with and it looks just fine . I got some glue on my finger and rubbed a thin layer of it on the bottle where the label would go . and just laid the label over it and gently rubbed over it to press it in place. You have to be pretty quick in doing it . You can slide the label a bit to get it in place , but if you piddle with it too long , you will get where you will not be bale to move it and possibly wrinkle the label or tear it . I am not recommending you do it that way , but that is how I did it and it came out fine . Of course if the label is brittle you could break it apart while trying to place it and I would say if you used too much glue it could soak through the label . My label was what I thought in very good condition and I had no problems with it .
Thanks for the input, I would say these labels are pretty sturdy, but had bottles in the past including a good "cure" that I didn't feel that way about.... Rather than mess with them, I just sold them barely hanging on, so to speak.
i use elmers just smear on a very light coating around the edges any residue on the glass wipes off with a damp cloth, super glue will cause bleed through just use the white stuff or a stick