Allergies seem to be our most unpredictable invaders. They attack us from nowhere, without a warning and leave us perplexed for reason. The worst part of the story is that an allergy might not be physically as harmful but the discomfort and at times, even pain it causes is simply intolerable.
As much hard as you might try, you just cannot fathom the cause of your attack. Though in some cases, it is easy to point out allergy to a certain food item or medication, but mostly it is difficult to point out the exact cause of the allergic attack.
If you want to solve the puzzle, most important thing to do is to retrospect and analyze the events just before the attack occurred. Did you have the same medicine just a few hours before you had that urticaria? The same could also apply for various other triggers such as food items and cosmetics.