Why are boiled eggs hard to peel?

A way to make it easier to peel boiled eggs is to use old eggs (about 3 days after purchase).
This is because the lower the pH of the egg white, the harder it is to peel, and the higher the pH, the easier it is to peel.

The pH of egg white is generally considered to be between 8.2 and 8.4 (*7.6 is also possible) for fresh eggs.
However, when the eggs are stored (for 2-3 days in a greenhouse), the CO2 in the egg white evaporates out of the eggshell, raising the pH to around 9.2, making it easier to peel the shell.
In addition, the boiled eggs are placed in cold water to avoid prolonged heating and to stop the generation of hydrogen sulfide.
To cool the egg quickly to prevent adhesion between the eggshell membrane and the albumen, making it easier to peel the eggshell.

From here on it’s subjective.

Another method was to pierce the egg with a needle, but this seems to be a method to prevent the egg from cracking while being boiled.
Moreover, the effect is not as expected.
* However, when steaming eggs, this hole is effective because it plays a role of letting air escape.

Also, if you need to cook fresh eggs immediately, it seems that you can add about half a teaspoon of baking soda to 1 liter of water to make it alkaline. (*However, the sulfide odor will increase.)