It can be difficult to tell when a cat has fleas, but even mild infestations can be detected by checking their fur and bedding on a regular basis.
Constant scratching is the most obvious indicator of fleas in cats, but this in itself doesn’t necessarily mean the problem is flea-based - and some cats carry fleas without scratching.
Hair loss caused by excessive grooming, and small, pepper-like specks (flea dirt) in your cat’s fur are all warning signs of a flea infestation. You may also notice a change in behaviour, including jumpiness and agitation, as well as red spots in its bedding where flea dirt has fallen off.
The best way to confirm a flea infestation is to run a comb through its fur (special fine-toothed flea combs are best), then hold it over a white surface like a piece of kitchen roll. This will let you easily spot any fleas or flea dirt that’s deposited from the comb. Flea dirt is essentially dried blood - if you add a few drops of water to the paper and the dirt turns reddish-brown, it’s very likely your pet has fleas.
Inspecting the skin under your cat’s fur may also reveal reddish bumps that can be a sign of flea bites, especially if your pet is allergic. Check its bedding for eggs - they are usually deposited in warm, humid places.