Jalopnik did an article on all the fluids in the car. In one of the sections it talks about engine oil. It breaks it out between conventional and synthetic and pulls quotes from Pennzoil's (dino) and Mobil1's (synth) Safety Data Sheets (SDS).
The Jalopnik article states when motor oil is clean (whether dino or synth), it is pretty much harmless to us humans. It states:
The first thing I found was that motor oil seems pretty harmless when it’s clean, with the Pennzoil data sheet agreeing with the Mobile1 sheet, which says inhalation, ingestion and exposure to skin are “Minimally Toxic.”
In fact, clean oil is so safe that the data sheets even said you don’t need to worry too much about skin protection. Here’s the quote from the Mobil 1 document:
No skin protection is ordinarily required under normal conditions of use. In accordance with good industrial hygiene practices, precautions should be taken to avoid skin contact.
The only even remote worry, based on Pennzoil’s safety data sheet, is that the oil could clog up your pores and give you a bad case of pre-teen acne:
Prolonged or repeated skin contact without proper cleaning can clog the pores of the skin resulting in disorders such as oil acne/folliculitis.
It also mentions that nausea, vomiting and diarrhea could result if you drink too much, and both sources say “mild, short-lasting discomfort to eyes” could occur if a gob of the stuff gets past your safety goggles. But in the end, clean motor oil really doesn’t seem so bad.
When the oil is used, all bets are off:
Then I got to the section about used motor oil, and things became much less pleasant. The data sheets say that, when oil is dirty—like it was when I wore and ate it—it becomes a carcinogen. Here’s what the Mobil 1 synthetic data sheet reads:
Oils that are used in gasoline engines may become hazardous and display the following properties: Carcinogenic in animal tests. Caused mutations in vitro. Possible allergen and photoallergen. Contains polycyclic aromatic compounds (PAC) from combustion products of gasoline and/or thermal degradation products.
And here’s Pennzoil’s remarks, describing why used oil is so much more dangerous than clean oil:
Used oils may contain harmful impurities that have accumulated during use. The concentration of such impurities will depend on use and they may present risks to health and the environment on disposal., ALL used oil should be handled with caution and skin contact avoided as far as possible. Remarks: Continuous contact with used engine oils has caused skin cancer in animal tests.
So basically, wearing clothes with dyed in oil and eating off of dishes with films of oil all over them really isn’t that bad. Unless the oil is dirty, in which case it is quite a terrible idea.
With this in mind, the article suggests there's no real difference between dino or synth oils as far as toxicity to humans. Both will not do much to you when clean, and both are not so good for you when dirty.