When should a kiss be offered as a greeting?

[JaimeMontoya]

Some people say hi or bye with a kiss in a very polite way (I mean male-female and female-male kisses, not same gender kisses). But sometimes people would just say hi or bye without kissing each other, just with a polite smile. I wonder if this is just a matter of culture. I am from El Salvador, so I would like to receive an answer with an western focus, since I know people from China or the middle east could have a very different culture and ways to say hi or bye. So what does ethics say about it? When should a kiss be offered as a greeting? When would it be inappropriate? I know that for family members it is a great custom, and a very positive one. But I mean in social life, like with your friends, and other people you meet in society, when they are not your family of course, nor a boyfriend or girlfriend. Thanks.

Jaime Montoya
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http://www.jaimemontoya.com