Because produce is porous so while you’re scrubbing it with soap, the soap is being absorbed into the fruit. That bit won’t wash off during the rinsing process. When you eat that it can cause issues.
If you’re literally using one drop of dish soap then you’re probably not going to have issues but still not great over time. Most people don’t use just a drop of soap or are filling the awful advice to soak produce in soapy water. You don’t want gastro issues from eating soap
As a general practice it’s a bad idea. Also water can’t really remove all the pesticides for the same reason, but that’s a whole different safety issue.
ok, gotcha, thank you for the reply! Generally we use water and a vinegar rinse. That’s what we use on berries, which are obviously a very porous fruit so I see what you mean about it absorbing soap, and that’s why I would never use soap on them. I guess I didn’t even think of it being a problem on apples because the thin seems so thick and I just use a tiny dab and rinse very well. I will just use the vinegar/water spray on that from now on, or water alone
Thanks for the tip- and also the tip about body wash in the soap dispensers. I'll try that, too.
Before eating, before cooking/preparing food, after each bathroom trip, after doing anything outdoors that results in dirty hands---say gardening or basketball, and upon returning home from certain outings, etc. That's got to add up to at least a dozen times per day, I would think. 
