For decades after it was discovered, penicillin was used to combat bacteria and, eventually, almost every other disease, whether it was the appropriate treatment or not. Over time and over use of penicillin and its successor drugs, resistant strains of bacteria began to appear, to the point where, now, many strains of bacteria are almost completely drug resistant.
According to a recent article posted to the Australian Broadcasting Corporation (ABC) site, nanosilver might become the 21st century’s penicillin, being widely used in the medical field, but also in consumer products, such as combs, hair dryers, men’s socks, and underwear.
Some of this overuse of nanosilver is probably due to companies simply following trends and wanting to appear cutting edge or it may be due to marketing efforts that fall into the "All New!" category. Other companies may be adding nanosilver as part of a genuine effort to improve their products and make them healthier, although how much healthier underwear is with nanosilver as opposed to underwear without is a debate probably best left to others.
While a total ban on the sale of products containing nanosilver, which groups such as Friends of the Earth propose is unlikely, (and frankly seems more like simplistic fear mongering than anything else), regulations on the amount of nanosilver in consumer products, based on the results of reputable studies and tests on the effects on humans and bacteria of prolonged exposure to nanosilver particles are needed.
Personally, I’d start by regulating the amount of silver nanoparticles in men’s underwear.