We cats live in a world of scent which you humans can never fully understand. You are nose blind to our smellscape! No wonder we are a bit of a mystery to you.
We can smell home. It smells of every human in the house (each with an individual scent signature), of every other cat or dog in the house, the regular cleaning fluids used, the regular food eaten - and our own scent.
We apply our body perfume by rubbing against corners, skirting boards, human legs, other cats or dogs, and furniture. That mixture is important. It makes up the family scent and reassures us that we are in a safe place, our core home.
So when you humans ruin it, no wonder we get stressed. Strangers coming into the house to service the boiler: new cats plonked inside the home: new smells you bring home after being in hospital (yukk smells like vet surgery!), spring cleaning (oh no!), or a new boyfriend/girlfriend with a strong perfume habit, or you add a floral plug in (purrlease....).
It smells wrong. The mixture is wrong, wrong, wrong.... to sensitive cat.
Try not to disrupt our important family scent mixture. It's our home, stupid.