Hormones are chemical substances that are secreted by the endocrine glands directly into the blood. These glands are ductless; therefore, it pours the secretion into the bloodstream. The hormones secreted are minute in quantities that are circulated in the blood and reach the specific target organ. Hormones are categorised into two types: Lipid-soluble: Examples include cortisol, testosterone, etc. Water-soluble. Examples include insulin, thyroid-stimulating hormone, follicle-stimulating hormone, etc.

The period during which boys and girls reach sexual maturity and become capable of reproduction is known as puberty. The onset of puberty is marked with several changes in the human body. In males, when the onset of puberty begins, the following characteristics are developed: deepening of the voice, facial hair growth, rapid increase in height etc.

Adolescence is the period when the body undergoes changes leading to reproductive maturity. Adolescents are also called teenagers because they cover the period of the teens i.e. 13 to 18 or 19 years of age.