Think about every piece of media that involves humans shrinking down to a fraction of their size: Honey, I Shrunk the Kids… Ant-Man… Fantastic Voyage… that Magic School Bus episode based on Fantastic Voyage. Now realise that all those characters should be stone dead. The laws of physics don’t care about whimsy or suspension of disbelief.
For starters: A shrink ray would have to compact the matter in someone’s body, or remove some of it. Both of those break fundamental rules of physics (conservation of mass and the Pauli exclusion principle, respectively). Can’t be done. Won’t be done. Moving on.
But let’s assume physics is feeling lenient today, and by some miracle, we have an adult human at 100th the size. Well, drastically smaller irises would let in almost no light, leaving your test subject near-blind. Adorably small vocal chords would produce sounds too high for most normal-sized humans to register, and shrunken cochleas wouldn’t be able to hear within in the range of a non-miniature human. Less surface area would lead to lower body heat, so, you’d be left with someone functionally blind, deaf, mute and shivering. Great job, Reed Richards.
Except there would be no time for any of that realisation to transpire during your madcap science experiment. At such a size, the haemoglobin in your test subject’s blood would be much, much smaller than the oxygen it’s intended to carry. In plain English, a shrink ray would kill anyone it was used on by asphyxiation. At the very least, this must come as wonderful news to supervillains.