What are the ingredients of beer and lager which preserve it?

If I drink too much beer or lager, which I believe have added-ins-or ons to preserve, it gives me a hangover which I didn`t want or paid for. What are the ingredients in the beer and lager that causes this?
I have made my own in the past and there`s absolutely no hangover next morning.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).