Young Chihuahua puppies and Chihuahuas with a genetic disposition for droopy ears have floppy Chihuahua ears. Mixed breed Chihuahuas also may have droopy ears. Adult Chihuahuas that normally have erect ears can have droopy ears from time to time as well.
Most Chihuahuas have erect ears by the time they are 6 to 8 weeks old, when the muscles at the base of the ears have matured. If the puppy has a long line of strong-eared ancestors, it also develops strong, standing ears. Chihuahua puppies in the teething stage may have ears that droop due to the discomfort of the incoming teeth and the constant chewing they do to relieve pain.