Originally Posted by Far-L

People are not allergic to peanuts as much as they are allergic to a mold that grows on peanuts. Everyone and anyone that enjoys too much peanuts in their diet can be harmed by this very toxic mold.

From the peanut butter wiki:

The peanut plant is susceptible to the mold Aspergillus flavus which produces a carcinogenic substance called aflatoxin.[14] Since it is impossible to completely remove all aflatoxin, contamination of peanuts and peanut butter is monitored in many countries to ensure safe levels of this carcinogen. In 1990, a study showed that average American peanut butter contained an average of 5.7 parts per billion of aflatoxins, well below the U.S. Food and Drug Administration limit of 20 parts per billion.[15][16]