Preconception Detox- Where are all the toxins coming from?

'Detox' has become a popular and catch all phrase to mean 'get healthier', 'get cleaner', 'prevention', and can be worn like a badge of honor, "I can't, I'm detoxing". Which I love, all of that is GREAT! But, WHY does someone need to detox, and how? Where are all of these so-called "toxins" coming from?