Vinegar is a natural ingredient that can help prevent and stop fleas. It doesn't kill fleas on your dog, but it helps repel them. Vinegar is acidic; it tastes bad and it smells bad. Fleas will naturally avoid it.
Add to Food or Water Bowl
You can add apple cider vinegar to your dog's food or water bowl. Vinegar consumption can change the skin balance, making your dog less palatable to fleas.
Apply to the Skin
If you don't want to add vinegar to your dog's diet, you can apply it to his skin and coat. Dilute white vinegar with your dog's shampoo and thoroughly lather him so the vinegar gets through all layers of his fur. Rinse thoroughly.
Cautions
When sneaking vinegar into your dog's water or food, you want to be careful to limit how much you give him, especially if your dog is old or has sensitive health. Too much vinegar can alter the body's pH level.
When using vinegar as a topical preventative, you will find it doesn't last long, so you'll have to apply it frequently. Too much vinegar on the skin can dry it out, which can increase problems for dogs with skin allergies or skin sensitivities.