std::stringstream vs std::string for concatenating many strings

I know one of the advantages of std::stringstream is that it is a std::istream so it may accept input from any type that defines operator<< to std::istream, and also from primitives types.

I am not going to use operator<<; instead I am just going to concatenate many strings. Does the implementation of std::stringstream make it faster than std::string for concatenating many strings?