When a cat encounters something or someone that frightens it, it will puff up its fur as a warning to prevent the other person from getting close. Of course, the muscles around the hair follicles will involuntarily tighten; this isn't a voluntary action. Once tightened, all the fur on the cat's body will stand on end. This is actually a defensive reaction in cats, designed to intimidate the other party and protect themselves.
As pet owners, we must be mindful that when cats are agitated, we must respect their feelings and never try to approach or get too close. This will make the cat feel valued. Therefore, pet owners must understand their cat's stress and anxiety to avoid causing them further fear and anxiety.
