My wife and I subscribe to Biblical Health Daily, which is a daily newsletter from the people at A week ago or so the newsletter said this (FYI):

How to Get Sick: Wear Tight Underclothing
Keeping your lymph system healthy is crucial when it comes to fighting off disease. Your lymph nodes are the first line of defense against toxins, viruses, and bacteria.
        Wearing tight underclothing can compress or block lymph nodes, which may stop the lymph system from properly cleansing itself. It is conceivable that this may help contribute to the development or proliferation of cancer in the body.
        Choose loose-fitting underclothing in breathable, natural cotton. Your body will thank you for it, and not just because it will help you stay healthy. Lightweight, natural fibers will keep you cool and comfortable too.