Some seeds and pits of fruits contain things like arsenic or other hazardous compounds....so that is why you do not want to include the seeds of apples. And don't feed the apple cores to your dog either. The white "pith" of the orange and other citrus is really bitter and has a nasty flavor if added to stuff. yep. you need to wash things well. As kids, we would eat the carrots out of the garden, wiping the dirt away on our jeans. Those skin on carrots always had an "earthy" flavor. I would make sure stuff was very well washed before juicing anything especially greens as they are more commonly the sources of food poisonings.