I, too got them after eating. I finally nailed down the cause. Mine are caused by ANY AMOUNT OF HYDROGENATED OIL. Partially or completely HYDROGENATED OIL, also known as TRANS FAT, or called TRANS FATTY ACIDS, or  labeled as MARGARINE and also VEGETABLE SHORTENING!  

This country allows many misleading ingredient lists to be used without anyone watching them.... and percentages less than a half gram per serving are being listed as "0".  

Where in any math class is "ZERO" equal to a "half gram per serving!"

(and the serving amount is decided upon by the manufacturer of the food)  To get under the half gram per serving rule they reduce the amount in a serving. Some potato chip bags say ZERO TRANS FAT on the label and list 7 chips as a serving!  

My point is they LIE!~  BUYER and EATER BEWARE!  In restaurants, the oil on the grill as well as in the deep fryer may say Zero Transfat, but if I eat any of it I break out in itchy hives that will turn into blisters!  This happens in less than an hour!

I bought REESE's Peanut Butter cups in the shape of hearts for Valentine's day. They had Zero Transfat on the ingredients, and they DID NOT LIST ANY HYDROGENATED OIL on the wrapper for the first time. I assumed stupidly that they had removed the hydrogenated oil, and I ate three of them. In 20 minutes I was itching and it takes weeks to heal!  I called Hershey's and they said that what is on the label is what they have listed in the computer, and there was no way to know what mistakes may have been made. They had no record of any changes to their original recipe, even though it was NOT ON THIS LABEL!   They promised to check it out and call me back.  They did not! Instead I got a $10 check in the mail for my complaint.  

Good thing the Hydrogenated Trans Fat just causes discomfort.  

Also McDonald's Grilled Chicken is listed as 0 transfat. The store level manager said he uses only water on the grill. Yet I got the hives!  I called the corporate office and they told me that the Grilled Chicken is sold to them frozen and pre-coated with Hydrogenated OIL!!!!!  They lie about it being free of transfat!   

 Start reading labels!  And start a food log. If you get a reaction again and again after eating certain foods or in certain restaurants, you probably nailed the culprit!

Now, don't even get me started about Propylene Glycol!  Swiffer cleans your floors with Propylene Glycol, but why is it now in most salad dressings and breads, cakes and tooth paste!  It is floor cleaner!  YUCK!  

If you ever want to check on an ingredient, go to OSHA.GOV and see what they say about the employees coming in contact with an overdose of any chemical product! Then ask yourself, why should I be eating this????