Mental health conditions are caused by a lot of different things, but at their core they are all caused by a change in how the cells in the brain communicate with each other. The change in communication can come from within (due to genetic factors), or as a result of a virus or outside agent that gets into the brain.

Our brains are made up of over 100 billion cells called neurons which pass information between themselves and process all the information we take in through our senses. These neurons are separated into brain regions, which all handle different things. For example, you have a visual area that processes your vision and a separate speech area that handles talking and language. These neurons communicate by passing signals between themselves using certain chemicals (neurotransmitters). If too much or too little of these chemicals are present, then the brain regions and neurons cannot function and communicate properly. This can sometimes lead to mental health conditions like schizophrenia.

Imagine you and 20 of your friends are trying to plan a party by texting. You and your friends all represent neurons passing information to each other through neurotransmitters (texting). If everything is normal, everybody communicates well and you can easily plan the party. Now, imagine that the cell phone services are behaving abnormally and each text is sent 150 times instead of once. Suddenly, communicating becomes difficult and the party is not planned as well. In the same way, if there are too many neurotransmitters present in the brain the neurons have trouble communicating and cause mental health conditions.

Each mental health condition has different neurotransmitters involved, but many scientists think that Schizophrenia is the result of differences in levels of two main neurotransmitters: dopamine and serotonin. Why this happens isn’t known, but it likely can be genetic, caused by an environmental factor, or a mixture of the two.

There are drugs that people can take to try to correct the imbalances of the neurotransmitters, and they work for a lot of people. They work different amounts for everyone though, and don’t work for all people. Other treatments (like Deep Brain Stimulation, where small electric shocks are given to the neurons that aren’t communicating to try to make them behave normally) are currently being developed and might provide better results.

In summary, mental health conditions are caused by changes in neurotransmitters that keep neurons from communicating properly. These changes might "get in" from the outside world (through a virus) or might come from the brain itself (genetics).