Cat whiskers are specialized sensory hairs called vibrissae.
They are much more important than ordinary fur.
The follicles are highly sensitive
The visible whisker itself does not contain nerves.
The important sensory structures are at the base.
When a whisker bends, movement transfers to a deeply rooted follicle surrounded by sensitive nerves.
Whiskers help with close-range navigation
Cats do not focus sharply on objects extremely close to the face.
Whiskers help fill in that gap.
They can detect objects, surfaces, and openings before the face collides with them.
They can detect air movement
Moving objects disturb the air.
Sensitive whiskers can respond to those tiny currents.
That gives a cat information about nearby movement even in dim light.
Do whiskers measure whether a cat can fit through a space?
Not as perfectly as the popular story suggests.
Whiskers are not guaranteed to be exactly as wide as the cat’s body.
But contact with the sides of an opening can still provide useful information.
Whisker position can show mood
Forward whiskers can accompany interest or hunting.
Pulled-back whiskers can appear during fear or defense.
Neutral whiskers often go with a relaxed face.
That is useful alongside signals such as slow blinking.
Should whiskers be trimmed?
No.
Cutting them removes sensory information.
They naturally shed and regrow without human help.
Whiskers are basically close-range sensory equipment built directly into a cat’s face.
And that’s the short explanation.
Related explanations: Why do cats slow blink?, Why do cats purr?, and Why do cats rub against people?