Which acids are naturally found in foods and can be safe to eat? ?

Which acids are naturally found in foods and can be safe to eat ?
Folic acid:

Ithink the correct answer would be that since the disease is passed by a hand shake and can be cured with antibiotics that it could be an infection. an example could be that once when i was working in a bush camp, i got blood poisoning from blood blisters that got infected. our cook did not wash his hands after going to the bathroom and he passed staphyloccus on to the crew he fed. one other person also got a bad similar infection on the side of his face. i had to be rescued by helicopter and taken to the hospital so i wouldn't die!

Keeps you from getting lung cancer from smoking