There are so many barriers to effective communication, sometimes I think it is remarkable that we manage to communicate at all! Since communication consists of a sender and a receiver as well as the external environment both are communicating in, let's go over a few barriers for each.
A person who is sending a message can create barriers a few different ways. First, the person can put up barriers with body language. The way we hold or move our bodies and the expressions on our faces can send a message that is inconsistent with what we are saying or can communicate in a way that is a barrier. For example, if I am welcoming someone into my home and have my arms folded tightly across my chest, that is not a welcoming gesture at all and the person receiving the message is less likely to hear my welcome, since we tend to respond more to body language than to words. Similarly, if I tell a friend that I like her dress and I am frowning when I say this, how receptive is she going to be to what I say? A second barrier is put up when we do not speak in a language that the listener can understand. By that, I do not mean a foreign language. I do mean that I should be speaking with a vocabulary the listener can understand, not using many terms that I know perfectly well the listener is not familiar with. I just finished reviewing an essay for a student who wrote almost entirely in initials and abbreviations most people would not understand. She was putting up a barrier to communication with her reader. I should adjust the complexity of my sentences to my audience, as well, speaking more simply to a child than I would to an adult. When we do not do this, we are creating a barrier in communication.
Listeners put up barriers, too. A common barrier occurs when we are thinking more about what we are going to say next instead of actually listening to what someone is saying. Another barrier occurs when we do not look at the speaker frequently. When someone is speaking, he or she expects to be looked at, and not doing so interferes a great deal. Additionally, the emotional state of the listener can be a barrier to communication. If a person is angry or sad, he or she is not going to be able to listen very well. This is a fairly common barrier in an argument.
The external environment is filled with barriers to communication, generally with distractions of various kinds. Being in a noisy club or in a classroom in which too many students are speaking at once create barriers to communication between any two people or communication to a group at large. There are other kinds of distractions, too, for example, the distraction of discomfort. Uncomfortable chairs or a room that is too hot or too cold gets in the way of effective communication.
Communication is an art, and understanding what the barriers are, for sender and receiver and in the general environment, goes a long way toward good communication.