Cats are great groomers and clean freaks. Their tongues are really rough specifically so they groom themselves with it. Because they are so good at grooming you won't often see a lot of fleas on them. There are a few things though that can give it away.
1. Look under their chin.
You'll often see live fleas here or flea dirt. It's the one place on their body that they can't reach to groom with their tongue or their paws. The fleas will often hide out here so lift up that chin and part the hair
2. Over grooming.
This occurs when cats groom excessively in 1 spot. The fleas irritate them so they lick the fur too much and the hair starts to thin out and eventually they will have bald patches. The most common areas for this to occur are the tailbase, the back of their thighs and the belly.
3. Check their bedding.
You may not see anything on the cat but the tell tail sign can be the flea poo left on your cat's bedding. Fleas feed on blood so their poo is black dirt. If it gets wet it will look like blood spots on the bedding. Where you see flea dirt there are fleas!
What should I do if my cat has signs of fleas?
If your cat has any of these signs of flea infestation you should apply a long acting flea treatment (eg. Frontline Plus, Revolution or Comfortis) and don't forget to treat all animals in the household.