Friends like Stephanie have told us of their experience of being able to reintroduce garlic flavour to their diet via black garlic. They had found raw garlic caused gastric side effects or allergic reactions. As Stephanie reports:

“Growing up my mother did not use much garlic in her cooking so I had no idea how  terribly allergic I was until I was at my future mother in law's home for the first time.
Being European everything was laced with garlic. I was consuming the lot not wanting to appear rude.
That night I was violently ill,  this condition lasted for two days. So sadly garlic was out of the question.
 
You can imagine my husband’s delight, being Austrian, to meet Jenny and Cathy at the Caravan Show in Sydney where we were introduced to Garlicious Grown Australian Black Garlic.
Still I wasn’t convinced and didn’t want to chance being ill again. We however did buy some product for Andy to try.
 
The following week he slipped the black garlic powder into a meal  he was preparing for dinner …
Result …the food was wonderful and I had no reaction at all!
 
I would highly recommend this product to anyone.”
Stephanie Greenbury
Artarmon

Why might this be? We know the caramelisation process of black garlic changes the chemical nature of the garlic with higher antioxidants and S-Allylcysteine, lower organic sulphur compounds (like allicin thought to cause garlic allergy) and lower ph. You can read more of the science of black garlic here. These changes make the garlic more digestible. We have friends who buy unpeeled cloves and eat one per day for the health benefits alone.

New research has focused on the anti-allergy properties of the black garlic itself. The authors conclude that black garlic itself has direct anti-allergy properties which may underlay Stephanie's experience. Read the detailed Korean study here.

Interestingly, there have been some similar results for turmeric as an anti-allergy spice - you can read an overview here. 
This is a brief review of recent research on black garlic and is not intended to claim any health benefits for black garlic. The review is provided for interest only.