Hormones are chemical substances in the body.
They are made by endocrine glands which pass the hormones directly into the bloodstream.
They are carried around the body in the blood and, in this way, hormones can cause changes at some distance from the gland where they were made.
Some hormones have long term effects, for example, the hormones that control how we grow and the changes that happen at puberty.
Other hormones have shorter term effects.