Fleas are the most common external parasite found on pets and can irritate your pet with constant itching and scratching, hair loss, or flea allergy dermatitis. Activyl® Spot-On for Dogs and Cats stops fleas from biting to give your pet quick relief and breaks the flea life cycle to prevent new fleas from developing. Activyl Spot-On for Dogs and Puppies is indicated for use once a month on dogs and puppies that weigh over 4 lbs. and are 8 weeks of age or older.