What are good undershirts to wear while on the body regimen? The main thing I am looking for is the least irritating undershirt. I would also like a shirt that does not show underneath a t-shirt.

Go and buy a cheap multipack of black and white vests. The black will get orangey bleach stains on the inside but sometimes you need to wear black if its showing through your clothes or anything. As long as they feel soft theyre not going to irritate 🙂

Dan says in one of his videos that it's a good idea to wear white t-shirts/vests underneath and then wear something you like over it like a sweater. It depends if that's your style though. Plus if it's hot you don't really want to be wearing two layers.

You could wear something like this if not, I have one similar. There's also ones with graphics on them that are still white everywhere else, so you could get a few variants of the same t-shirt so you don't look like you're wearing the same clothes everyday. The neckline is pretty low too so it won't rub against the treated area.