Hard lumps on skin

I noticed while stroking her that one of our friend's cats has lumps under her fur - small ones on the head/collar, and a few larger ones along the top of her back, towards her tail.

At first I thought they were just burrs (but she grooms excessively, so this seems unlikely), or old scabs. It didn't bother her to have them picked at when I was exploring! But there seemed to be quite a lot of them, and they definitely felt round, rather than the random shape of scars from cat fighting (she is an indoor/outdoor cat).

I wonder whether they could be flea bites? Or some other type of insect bites?

Does anyone have any ideas as to what they might be?

They could be old scars that got infected around them and bumped up, insect bites, fatty tissue deposits or worse, it would definitely be worth having a vet check them to see

I would have them checked out. Any unusual lumps and bumps are a pretty immediate vet visit at our house.

They may just be cysts but I would have it checked out. One of my cats has these, one just opened recently, very strange white clay like stuff came out. The vet said not to worry about them.