The reflection is nearly always wrong in some way, and that wrongness is what readers work from: a dream about self-image rather than about appearance.
What dreamers remember from a mirror dream is rarely the mirror. It is the face looking back: older, younger, a stranger, or lagging half a second behind. Interpreters treat the image as a dream about self-image, about the distance between how somebody sees themselves and how they believe they appear, and that account holds remarkably steady across very different sources.
Almost every reported variant involves the reflection failing somehow. A face that is not yours has long been associated with a stretch of not recognising your own behaviour. A reflection moving independently gets linked to feeling watched, or to playing a part. Seeing yourself much older suggests a preoccupation with time rather than a statement about it, and seeing yourself as a child is generally connected to something unfinished from those years.
A cracked or shattered mirror is the most feared version, and the superstition around broken glass gives it extra weight. Dream commentary, though, treats the break as self-image under strain rather than as seven years of anything. Covered mirrors show up in the dreams of people from cultures where mirrors are draped during mourning, and there the image belongs to grief and its customs rather than to any general symbolism.
A fogged or dirty mirror, common enough after a bathroom mirror steamed up the night before, tends to point towards uncertainty about where you currently stand with yourself.
Mirrors already mean different things to different dreamers before interpretation begins. Somebody who spends an hour in front of one for work, an actor or a dancer, has a working relationship with their reflection that a person avoiding mirrors altogether does not. A dreamer recovering from an illness that altered their appearance reads the image through that. The tradition offers a set of suggestions, and the suggestion fitting your own history is the one to keep.
None of it diagnoses anything, and a mirror dream says nothing whatsoever about how you actually look.


