DD1's undies have been handed down to DD2. All their clothes get washed together, including undies, so if there was any ickiness to be passed on, it would have done so by now

In fact I am now in a dillemma with the undies that DD2 is growing out off. Normally everything either goes to an op shop or a friend, but I was unsure about the undie issue (even though I have passed on nappies)