Fleas are bothersome pests for pets and humans, and homes can become infested. Scientific studies that the scent of thyme, mint, yarrow, and myrtle are effective flea repellents. The herbal oils extracted from common thyme and lemon thyme have scents that fleas avoid. Any cultivar from the Mentha plant family—peppermint, spearmint, pineapple mint, and more—contains oils that produce smells that fleas hate. Yarrow plants, while lovely with feathery foliage and colorful blooms, do not have a particularly pleasant scent to humans or fleas. Myrtle: Often called sweet myrtle, the oil has a sweet, fresh, green, and slightly camphorous scent fleas tend to avoid. Eucalyptus: Similar to myrtle oil, eucalyptus oil has a fresh, minty, woodsy, slightly sweet note that fleas hate. The herbal scent of basil oil is not pleasant to fleas. Lemongrass oil contains citral and geraniol notes that repel both fleas and other insects. The pungent, piney smell of rosemary is a natural insect repellent. Pine oil is a good choice for cleaning products because fleas hate the smell.