Milk

• Milk and its byproducts, whey and casein, are common allergens. Milk chocolate produced in the United States and Europe contains as much as 10 percent milk.
  
  

Nuts

• Nuts, another common allergen, are often found in chocolate bars. However, even if no nuts are listed in the ingredients, traces can still be found in the chocolate if the chocolate was made in a factory that also manufactures nut products.
  
  

Wheat and Gluten

• Wheat and gluten are also allergy triggers and are common ingredients in mass-produced chocolate candies.
  
  

Soy

• Soy is another common allergen. Soy lecithin is an ingredient found in many popular chocolate bars and other chocolate products.
  
  

Corn

• Corn, especially corn syrup, is another ingredient and allergen found in many popular chocolate bars and in other products containing chocolate.