1 Egg white intolerance
Some people have egg white intolerance. These people might have no problem eating the egg yolk.
2 Lack of fiber
Some people have sensitive stomachs or intestinal problems. These people might feel better if they ate food containing fiber along with eggs. See also why green tea makes some people sick.
3 Egg allergy
Eggs are among the top foods causing allergies. If a person is allergic to any part of the Egg then he might feel sick after eating them.
4 Egg yolk sensitivity
Some people are sensitive to the egg yolk but have no problem eating the egg white.
5 Egg protein sensitivty
Some people are sensitive to egg protein. Their bodies consider the egg protein harmful foreign bodies, and as a result, their immune system is triggered when they eat eggs.
6 They are mixed with the wrong food
Eating eggs, which are very rich in protein, along with another protein rich food can cause disturbances to some people.
7 Eating them on an empty stomach
Some people experience stomach pain when they eat Eggs on an empty stomach. Eating something before eggs can eliminate this problem.
8 Can trigger histamine
According to Wikipedia, egg whites can trigger the release of histamine, a compound involved in immune response, from mast cells. The side effects of that can be abdominal pain and diarrhea.