The Chihuahua is the smallest breed of dog in the world, but despite its small size, it has a big heart and a strong personality. The Chihuahua’s origins date back to Mexico, where it is believed to be a descendant of the ancient Techichi dogs bred by the Aztecs and Toltecs. Modern Chihuahuas are named after the Mexican state of Chihuahua, from where they spread to the USA and later to the whole world in the 19th century. Despite their small size, the Chihuahua is bold, lively and confident. They often have a strong protective instinct towards their owner and are very loyal. However, some individuals can be jealous or fearful if they are not properly socialized. Interestingly, they have the largest brain in relation to their body size of all dogs. The breed has a relatively long lifespan – often living to 14 to 18 years. However, they can suffer from problems with their teeth, heart, collapsed trachea or luxated uvula.