Most scientists agree that sexual orientation (including homosexuality and bisexuality) is the result of a combination of environmental, emotional, hormonal, and biological factors. In other words, many things contribute to a person's sexual orientation, and the factors may be different for different people.​Homosexuality and bisexuality aren’t caused by the way children were reared by their parents, or by something that happened to them when they were young. Also, being homosexual or bisexual does not mean the person is mentally ill or abnormal in any way. They may face burdens caused by other people’s prejudices or misunderstandings.

How Do People Know Their Sexual Orientation?

Many people discover their sexual orientation as teens or young adults, and in many cases without any sexual experience. For example, someone may notice that their sexual thoughts and activities focus on people of the same sex, or both sexes. But it’s possible to have fantasies or to be curious about people of the same sex without being homosexual or bisexual. And they may not pursue those attractions.