While they claim it's possible to wear 100 days straight without washing, no one is going to force you to wear it 100 days straight or 3 days a week. It's just a shirt made from wool. Wool doesn't retain odors and sweat the same way cotton or synthetics does. Think of it like a wool sweater, how many wears do you get out of it between dry cleaning? I like wool a lot but am still a little skeptical of their claims. We'll see though.