I studied this book, "Biophyical therapy of allergies" by Peter Schumacher, M.D.
You can find this book in Google books http://books.google.com/books/about/Biophysical_therapy_of_allergies.html?id=tu3uQZcp_REC
However not every single page is viewable due to copy right. But they are good enough.
I strongly suggest you should have a throughout read of the Chapter of Neurodermatitis (濕疹), starts from page 175.
On page 177 it says: "Besides chronic allergies, which are always the source of neurodermatitis, the same patient also experiences imposed acute allergies. They may be caused by various foods (e.g., citrus fruit, tomatoes, chocolate). They may change during the course of the disease; that is to say, they appear and disappear causing an exacerbation of the skin condition. Yet, they are never the acutal cause of neurodermatitis. Substances that affect the skin topically (e.g., ointments, cosmetics, textiles, laundry soap) may act as acute allergens. The same situation applies for them, as did for the acute food allergens."
And the rest of the chapter talks about cow's milk, wheat and fungal allergies. It is not an absolute rule that cow's milk allergy appears on trunk and wheat appears on face. It is just a general saying. Sometimes it can be the whole body (if you look at those pictures). Everybody is different.
There is a highlight in the chapter he wrote: "However, true healing is only possible if the cause of the disease - the allergy - is eliminated!"
hope it help.
Also for henry102, there is a chapter whick talks about urticaria.