Hello and thank you for using HCM! From the information you provided (blood examinations, other examinations are OK) it seems to me that this is some kind of allergic reaction. Even though the allergy specialist ruled-out allergies, this does not mean that it is like that. Why? Because many forms of allergies cannot be diagnosed or detected and the number of allergy test is limited. Since the swell retracts by using Zyrtec, then this supports the allergy hypothesis. Such allergy could be caused by virtually anything found at home or outside, some ingredient in the food of the baby, potential medications or their compounds, etc. What I suggest is the following: note down (or observe carefully) to what is exposed your baby when allergic episodes occur. This could take a lot of time and patience until you will spot the factor responsible for the swelling. Once you find it then it will be easier to manage your baby s condition. I hope my suggestion will help you, Thank you and good luck!