Q. I've noticed that my 18-month-old daughter already seems to be growing a breast on one side! Is something wrong?
A. I've seen this many times in my practice. Your daughter probably has something called benign premature thelarche -- medicalese for early breast development that's nothing to worry about.
In most cases, it's thought that small amounts of extra hormones cause breast tissue to grow for a few months. After that, the extra tissue either goes away by itself or remains as a small nubbin until puberty, when it develops into a normal-size breast.
There are some serious causes of breast tissue in toddlers (who don't usually have any at all), though, so do have your doctor check it out. A sudden jump up a height percentile or two can mean a significant hormonal problem. So can signs of puberty, such as pubic or underarm hair. If you notice either, or if your daughter's breast seems to be growing rapidly, call the doctor right away.