Despite rumors to the contrary, there is no medical evidence that the Chihuahua breed of dog is capable of curing asthma. It is true, however, that the Chihuahua has less fur than many other breeds and is therefore apt to be less aggravating to those whose asthma makes them sensitive to the byproducts of shedding.
According to Animal Planet, many people believe the Chihuahua is either able to reverse asthma in some way or to "absorb" the condition in much the same fashion a sponge absorbs water. Some people even believe that allowing the dog to sleep with or on the chest of an asthmatic child is likely to lead to curing the child of his or her condition.
Animal Planet reports that the Aztecs regarded the Chihuahua as a spiritual guide that assisted the dead by "absorbing" their sins and suggests this is where the asthma cure rumors started. The dog breed is also apt to make wheezing sounds when it breathes, possibly leading some to believe that it takes on the condition from its human hosts. Meanwhile, the fact that a number of children with asthma eventually outgrow their condition might have appeared to confirm the belief that the family pet had taken on the condition.