Epigenetics is any process that alters gene activity and expression without changing the DNA sequence.
There are different types of epigenetic processes. Some of the major ones include methylation, acetylation, phosphorylation, ubiquitylation, and sumolyation.
It is likely that other processes will be revealed as research and studies proceed.
Epigenetic processes are natural and essential to many organism functions. The thing is if they are occuring improper, there can be adverse health and behavioral effects. Many of these health concerns relate to mental health.
With research, we know that the chemical reactions and environment that starts in the womb can determine which genes get expressed and which get silenced in the tissues and organs.
Not only that, but environmental factors can alter gene expression anytime throughout a person’s lifespan.
A good place to start learning is the article Epigenetics: the Science of Change.
You can also follow my link to learn more about methylation: