Pi eggs are a unique Chinese processed egg product and an alkaline food. The ingredients needed for pickling leather eggs are salt, tea, and alkaline substances (e.g., quicklime, grass ash, sodium carbonate, sodium hydroxide, etc.).

Skinned eggs have a special flavor because after the strong alkaline action, the sulfur-containing amino acids they originally had are broken down to produce hydrogen sulfide and ammonia, which, together with the smell of the ingredients in the impregnating solution, creates the characteristic flavor.

In order to promote protein coagulation, eggs are made with ingredients that contain lead oxide and lead salts. (In the preparation of skin eggs, the auxiliary material wrapped around the outside of the fresh egg contains something called mitochondria, which is chemically composed of lead oxide. During the process of making and placing, this lead oxide gradually penetrates into the egg.

It has been determined that each gram of eggs contains about 3 micrograms of lead, and each egg contains about 180 micrograms of lead if it is 60 grams). After inhaling trace amounts of lead for a long period of time, the human body will cause obvious harm to the nervous system, hematopoietic system and digestive system.

As for the "lead-free eggs", they are not free of lead, but contain much less lead than the traditional pickled eggs.

Traces of lead have little effect on the health of adults, but for children, lead-free eggs should be eaten sparingly or not at all, because children are very sensitive to lead, and the absorption rate in the intestines is as high as 50%.