Cat losing hair? Medical not shedding?

Im asking this question for my dad-inlaw…He just bought collars for his cats not long ago- same rack-brand-all of it his one cat we’ll call Cat1 had started to breakout you could say losing fur has/had some sores fur loss completly around neck some on his back and near his tail- its looks as if hes been chewing. Cat 2 never had any problem totally fine. He says this happens sometimes in the summer with Cat 1 and had another one who had the same problem but has never been this severe. There has been NO Flea evidence. He obviously has taken the color off since this has happened a few weeks ago and had given them their Frontline treatment recently. Cat 1 has started getting better and fur is growing back since then.A friend of his mentioned possibly Sand Fleas but there is no evidence of fleas. I am a groomer which is why he asked me but I dont deal with cats- Im figuring its an allergic reaction from something that was possibly on the collar or some kinda Mange but why would the Mange get better once Frontline is applied? If anyone has any suggestions as to what possibly couldve happened please let me know! Once again there was NO sign of fleas once Frontline was applied Cat1 has gotten better and this happens during the summer sometimes.THANK YOU FOR YOUR ANSWERS!!

Hi Michelle,

Hair loss can be a variety of problems. Was the collar a bit tight by chance? Other than that, with hair loss at the neck and base of tail, it sounds like it could be a topical parasite (such as mange), and more are not diagnosed based on sight alone, many of them need skin scraping samples examined under the microscope, however they are generally treated with a topical deworming product, such as Frontline, though it generally takes more than one dose.
It could also be a behavioural problem as well, such as psychogenic alopecia, or hair pulling/chewing or other behavioural problems. If it is deemed behavioural, then medical problems must be ruled out and then a behaviour exam done to try to find the root of the issue, then usually treated with a short-term of behaviour altering medications that are very effective for these sorts of problems.
Though with all this being said, I would be surprised that if one cat had a topical parasite that the other one doesn’t show any evidence of it as they can be quite contagious (mange is also contagious to humans!).
Since it has improved, I would just keep an eye on it, but if/when it does reoccur, I would take the cat(s) in for a check-up.

All the best!