No, not always. Often, you only see part of the mold on the surface of food -- gray fur on forgotten bologna, fuzzy green dots on bread, white dust on Cheddar, coin-size velvety circles on fruits, and furry growth on the surface of jellies. When a food shows heavy mold growth, “root” threads have invaded it deeply. In dangerous molds, poisonous substances are often contained in and around these threads. In some cases, toxins may have spread throughout the food so you should throw it away.

Recommended Resources:

http://www.fsis.usda.gov/Fact_Sheets/Molds_On_Food/index.asp