A fresh egg tends to stick to the shell when boiled due to its high acid content. As the egg ages, carbon dioxide and moisture inside the egg gradually leak out through the thousands of tiny pores in the shell. This lowers the acidity inside the egg and makes it less likely to stick to the shell when boiled. The contents of the egg also shrink slightly due to moisture loss. Air that diffuses into the egg through the shell creates a larger air cavity at the end of the shell, which further makes peeling easier. Avoid using the freshest eggs when boiling eggs and instead use those you've had for two or three days.

Boiling affects the pH level inside the egg, lowering the acidity, similar to the process in aging. Undercooked eggs are more likely to stick to the shell as they are more acidic than those that are cooked for a longer time. This does cause a slight problem because overcooking hard-boiled eggs makes the white of the egg rubbery and may create a green ring around the yolk. Adjusting your cooking time may make hard-boiled eggs easier to peel.

Making a pinhole in the large end of the shell before boiling the egg makes shelling easier. Because the large end of an egg has an air sac between the contents of the egg and the shell, pricking does not cause the egg contents to seep out. When you prick the shell of the egg before boiling, some water seeps into the egg between the shell and the contents of the egg, making it easier to peel when boiled, notes Exploratorium's Science of Cooking.

Eggs continue to cook even after taking them out of the boiling water, unless you cool them quickly. Plunging them into cold water stops the cooking process and makes the eggs easier to peel. If they still resist shelling, cracking them gently to loosen the shell and holding them under cold running water typically makes shelling easier, as the water works as a lubricant to slip the egg free of the shell.