So all 3 of my cats started getting itchy back at the end of december. scratching and overgrooming, one has half of the hair on his back legs gone from grooming, they all have little sores/bumps. Took them to the vet on jan 5th, they didn't find any fleas or see anything in a skin scraping. They were on prednisolone for 3 weeks and antibiotic for 2 weeks, the condition improved but started coming back after the meds wore off. So the other day I took them back in, more steroids and antibiotics, still no sign of fleas. this time my vet sent in a skin biopsy. and blood from one of the cats for an allergy test. They've settled down now since they are on meds again. It looks like some kind of allergy but what are the chances of all 3 cats developing an allergy all at the same time? could it be something other than an allergy?