The Yorkshire terrier originated in Scotland as the Waterside terrier but acquired its current name after being brought by immigrants to the area of Yorkshire, England in the mid-1800s. There it underwent changes resulting in the standard Yorkshire terrier we see today. Although considered a toy breed, the Yorkie was originally a working dog employed as a rat-catcher in textile mills. Though more likely a pampered pet now, the Yorkie remains a vigorous, energetic and generally healthy little dog.
The American Kennel Club weight standard for Yorkshire terriers states they cannot "exceed 7 pounds." Due to unethical breeding of undersized Yorkie "runts" -- whose resulting offspring more often than not suffer serious health issues -- most reputable breeders and Yorkie organizations consider breeding of dogs smaller than 4 pounds unethical.
Teacup Is an Adjective
Yorkies are in the toy group, but the AKC does not recognize "teacups." No such creatures as "teacup," "micro" or "mini" Yorkshire terriers exist. Those are merely unofficial adjectives prefixed to the name Yorkshire terrier by unscrupulous breeders aiming at persuading prospective buyers to pay more for a tiny Yorkie.
All Yorkshire terriers are susceptible to some health issues -- including eye disease and patellar luxation -- though, for the most part, Yorkies are healthy, long-lived dogs whose average life span is 12 to 15 years. The general health and longevity of "teacup" Yorkies is another story. Due to their extremely small size, organs and bones are proportionately tiny and often do not function as well as those of their full-sized counterparts. Hypoglycemia is common as are severe liver problems, bone breakage, heart and respiratory problems. In addition, teacup-sized dogs tend to die younger. Females and their offspring often die during the birthing process itself -- as a result of inadequately sized reproductive organs.
Care of Teacup Yorkies
If you simply must have a teacup Yorkie, be prepared to spend both time and money caring for your diminutive pup. Teacup Yorkies require the use of a harness rather than collar to avoid throat injuries; frequent, specialized meals to prevent hypoglycemia that could lead to fainting or coma; careful handling by adults -- these are not dogs for children, who may drop them; sweaters and warm bedding to keep body temperature normal when weather is below 68 F; protection from sun in summer heat; mild exercise that will not tax their strength; and regular veterinary checkups to find and treat any problems before they become serious.