U.S. stocks fell on Tuesday after Federal Reserve Chairwoman Janet Yellen and her fellow Fed policymakers raised concerns about "substantially stretched valuations" in some sectors.
In the monetary policy report accompanying her congressional testimony, Yellen said that "equity valuations of smaller firms as well as social media and biotechnology firms appear to be stretched."
The Russell 2000 small-cap index dropped 0.8 percent and the Global X Social Media ETF slid 0.9 percent. Facebook shares tumbled 0.8 percent to $67.34. Twitter Inc shares slipped 0.4 percent to $38.16.