In aesthetics, the uncanny valley is a hypothesized relationship between the degree of an object's resemblance to a human being and the emotional response to such an object.
The more it resembles a human, the higher the observer’s affinity will be. Until the point where the humanoid object appears almost, but not exactly, like a real human being. This elicits an uncanny, or strangely familiar, feeling in observers.
After cosmetic procedures, the face can change in such a way that we also get the same uncanny feeling. The feeling that something is not right. That feeling could resemble the phenomenon we know from the uncanny valley.
As humans, we are evolutionarily capable of recognizing danger quickly. When something or somebody looks human, but displays traits that are a bit off, we recognize this immediately. This uncanny feeling arises when we see someone whose face no longer has the typical mobility that belongs to a human face. Which can be due to excessive Botox use.
When large amounts of fillers are placed, the volume in the face does not match other signals that the body gives about a person's age. The skin folds and shapes differently than we are used to. The whole thing gets even weirder when the eyebrows are extremely lifted. Major surgical procedures can also contribute to an 'uncanny' sensation. Think, for example, of a very tight facelift and an extreme rhinoplasty where a nose is created that is hardly possible by nature.