Would (a human) eating garlic repel dog/cat fleas?
(I couldn't find any reliable information on this, but I found that studies failed to show the same effect with mosquitos, despite popular belief that this works)
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Not sure about fleas, but it could well repel other humans – which might also be a good thing...
In all seriousness, I would consider it unlikely for this to be effective on the basis that cat and dog fleas, while not host specific, do not like to live on humans. Certainly they can bite humans and cause reactions in humans, but if garlic were to deter fleas, it would presumably be upon either landing on the human or ingestion of their blood. Sure, garlic could repel them at this stage, but they were likely to leave anyway because they had landed on a human, rather than a furry pet. And it wouldn't likely stop another flea from trying you out too.
Topical application of garlic or garlic-based product to a human, could well repel fleas and other insects, although any literature in support of this use is lacking. Any serious research into this effect is unlikely to take place, for obvious reasons.
There was a recent article (2020) which reviewed the literature - Can garlic prevent, repel or kill fleas that infest dogs? No studies were identified that directly assessed the efficacy of garlic in flea control in dogs, or suggested any merit in its use.
It is worth emphasising that garlic can be very toxic to dogs and especially cats, so never feed or apply garlic-based products to your pets.