why do some eggs need to be refrigerated and some don’t?

Question

I’ve been curious after seeing non-refrigerated eggs in Japan

In: 2

Answer 1

2 Schools of egg processing-

One says the outside of the egg can get dirty with chicken poop and other things, and thus can be a health concern. Thus they are washed. That removes the poop and dirt, but also the protective coating they have. These now need refrigeration

The other does not wash the eggs, keeps the coating, and allows them to not require refrigeration.

Different countries have different rules/laws on how they have to be processed.