It depends on why, specifically, you're sensitive to chocolate (see Do Chocolate Allergies Really Exist?).
Cacao beans are processed into two major components to make chocolate: cocoa powder and cocoa butter. Most of the proteins, phenolic compounds, caffeine, sugars, minerals, and flavor compounds of the chocolate are found in the powder. So if you happen to be sensitive to a component that is carried in the cocoa powder, you may find that white chocolate -- which contains no cocoa powder -- is a better alternative for you. This is unusual, however; much more common are allergies or sensitivities to other ingredients in the candy-making process.
White chocolate candies are not pure cocoa butter. They almost always include milk and sugar (or corn syrup) and often include soy lecithin. As with all candies, those with peanut allergies, tree nut allergies, wheat allergies, corn allergies, or celiac disease should be sure to check for cross-contamination on manufacturing lines before eating high-risk foods like chocolates.
What if you're pretty sure none of these foods are problematic for you, you're sure you're sensitive to chocolate, and you'd like to try adding white chocolate to your diet? Your next step is to give your internist or allergist a call. She can advise you of any precautions you may need to take given the nature of your prior reactions (whether they were allergies, intolerances, or sensitivities) or arrange for in-office testing.
Source:
McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen. "Chapter 12: Sugars, Chocolate, and Confectionary." Rev. Ed. New York: Scribner. 2004.
