Canine identification chips are small microchips that are placed just under a dog's skin. They're most commonly used by shelters to identify lost dogs so that they can be returned to their proper owners, and by laboratories to distinguish between dogs that look similar. While the safety testing of identification chips and their effects on dogs isn't complete, there have been reports of side effects in some animals.
According to the Vet Info website, some studies have shown that a small number of mice and rats have developed tumors at the microchip site, and one report showed tumors in two dogs that had microchips placed under their skin. However, in only one dog could the tumors be linked to the microchip. (The tumors in the other dog were thought to have been caused by multiple rabies shots.) There is no conclusive evidence linking microchips to cancer, but anecdotal evidence makes cancer a concern of many pet owners, and further studies are being conducted
Some dogs with identification chips have shown allergic reactions, but this is very rare. Bio-compatible glass is used to encase the microchip and make it safer for the animal. Swelling and itching commonly occur after a microchip injection, but they usually subside within a couple of days.
Infection has been known to occur at the microchip site, but it is very rare and can be treated with antibiotics. There is some concern that microchips will migrate through tissues and organs because of the dog's movement, but the risk of this is low. Hair loss was found in one animal over the course of a ten-year study, but evidence was inconclusive as to whether the microchip was to blame.
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