Of all age groups, infants are the most vulnerable to fluoride toxicity. Due to their small size, infants receive up to 400% more fluoride (per pound of body weight) than adults consuming the same level of fluoride in water. Not only do infants receive a larger dose, they have an impaired ability to excrete fluoride through their kidneys. Healthy adults can excrete more than 50% of an ingested fluoride dose; infants, by contrast, can only excrete 15 to 20%. This leads to a greater build-up of fluoride in the body, and may help explain why infants fed formula made with fluoridated water suffer higher rates of dental fluorosis, a discoloration of the teeth caused by excessive fluoride ingestion during childhood.