Ingredients for corned beef: cinnamon stick, mustard seed, black peppercorns, cloves, allspice berries, juniper berries, bay leaves, ground ginger
, beef brisket, onion, carrot, and celery.
If a person can eat other forms of beef consider above ingredient. Read the recipe. While any of these could be the issue, mustard seed allergy is increasing. An allergist can test and help you investigate.