What Happens When You Put Liquid Flea Medication on a Dog's Back?

That once-a-month topical medication keeps him flea-free.
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Putting topical flea medication between your dog's shoulder blades is one of your warm-weather monthly rituals. You know the liquid keeps fleas off your dog and gets rid of flea eggs, but if you consider how it actually works, you'll know why it's important to ensure that the flea medication ends up on your dog's skin and not on his hair.


Although various common liquid flea products might contain different chemicals, they absorb into your dog's skin the same way. These medications work by affecting the flea's central nervous system, causing death. Some contain growth regulators that prevent flea eggs from developing into adults. Even though you might place the liquid flea medication on only one or two areas of your dog, the oil in his skin spreads it throughout the body in a matter of 24 hours or more. The medication stays in his oil glands or hair follicles for a prescribed amount of time, generally until the next application date.


Spread the dog's hair so you can apply it to the skin between the shoulder blades. Some will inevitably get on the hair, but you don't want the product to coat the hair. Always follow the manufacturer's directions when applying topical flea control. Wear gloves when applying the product, or wash your hands very carefully afterward. Wait at least two days after applying flea control before bathing your dog. Bathing him sooner might interfere with skin absorption of the product.