Adolescence (from Latin: adolescere meaning "to grow up")is a transitional stage of physical and psychological human development generally occurring between puberty and legal adulthood (age of majority). The period of adolescence is most closely associated with the teenage years, although its physical, psychological and cultural expressions can begin earlier and end later. For example, although puberty has been historically associated with the onset of adolescent development, it now typically begins prior to the teenage years and there has been a normative shift of it occurring in preadolescence,(generally ends with the beginning of puberty, but may also be defined as ending with the start of the teenage years) particularly in females (see early and precocious puberty). Physical growth, as distinct from puberty (particularly in males), and cognitive development generally seen in adolescence, can also extend into the early twenties..

Puberty is the process of physical changes by which a child's body matures into an adult body capable of sexual reproduction to enable fertilization. It is initiated by hormonal signals from the brain to the gonads; the ovaries in a girl, the testes in a boy. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sexual organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when the child has developed an adult body. Until the maturation of their reproductive capabilities, the pre-pubertal, physical differences between boys and girls are the genitalia, the penis and the vagina.
The major landmark of puberty for males is the first ejaculation(ejection of semen (usually carrying sperm) from the male reproductory tract, and is usually accompanied by orgasm), which occurs on average at age 13.[1] For females, it is menarche , the onset of menstruation, which occurs on average between ages 12 and 13. Girls experience menarche at different ages. The timing of menarche is influenced by female biology, as well as genetic and environmental factors, especially nutritional factors.
Puberty which starts earlier than usual is known as precocious puberty. Puberty which starts later than usual is known as delayed puberty.

Dehydroepiandrosterone is an important endogenous steroid hormone. It is the most abundant circulating steroid in humans, in whom it is produced in the adrenal glands, the gonads, and the brain, where it functions predominantly as a metabolic intermediate in the biosynthesis of the androgen and estrogen sex steroids. However, DHEA also has a variety of potential biological effects in its own right, binding to an array of nuclear and cell surface receptors, and acting as aneurosteroid. It also influences the growth of pubic, axillary (under arm) and facial hair. It also contributes to faster body growth, oilier skin, and development of body odor.
Boys and girls have both types of hormones, but girls have higher levels of estrogen, and boys have higher level of androgens.
Primary sex characteristics for women includes the ovaries, fallopian tubes, uterus, clitoris and vagina. For male are the penis, testes, scrotum, seminal vesicle, and prostate gland.

Signs of Puberty:
For girls. * Breast Growth: A young girl develops breast buds growing from the nipple outwards early in puberty. Nipples will enlarge and darken, and the breasts continue to grow throughout puberty. * Body and Facial Hair: Pubic hair is the first to appear, followed by underarm hair and darker leg hair. Some girls will also develop slightly darker or coarser facial hair, but not with the density young men develop. * Vagina and Ovary Growth: This internal growth cannot be seen, but some regular abdominal cramping may occur and whitish secretions may occur before the onset of menstruation. * Menstruation: A girl's first monthly period may only last a few days, and her cycle is generally irregular for the first two to three years of puberty. * Body Shape Changes: A young woman's body becomes curvier during puberty as her hips widen to help enlarge the birth canal in preparation for sexual reproduction. * Body Odor and Acne: As hormone levels change and sweat glands mature, body odor becomes more noticeable and acne may develop.

For boys: * Testicle Growth: Testicles enlarge and grow more pendulous early in puberty. * Body and Facial Hair: Pubic and underarm hair is the first to appear, followed by chest and abdominal hair. A few hairs can indicate the onset of puberty, and hair will gradually thicken, darken, and spread for several years. * Growth Spurt: The hands and feet are the first to grow, often resulting in clumsiness. The arms and legs then lengthen, and the trunk is the last to grow to adult proportions as the shoulders broaden and chest deepens. * Weight Gain: Young men develop heavier bones and denser muscles during puberty, resulting in significant weight gain. * Body Odor and Acne: As hormone levels increase and sweat glands change, body odor becomes more noticeable and bouts of acne may appear. * Voice Change: The growth of the larynx results in a young man's voice dropping approximately one octave during puberty. * Breast Growth: Young men may experience some minimal swelling of the breasts during puberty as hormone levels increase and muscular density changes.

Signs of Sexual Maturity:
The principal sign of sexual maturity in boys is the production of sperm. The first ejaculation, or spermarche, occurs at an average age of 13.
The principal sign of sexual maturity in girls is menstruation, a monthly shedding of tissue from the lining of the womb. The first menstruation, called menarche, occurs fairly late in the sequence of female development ; its normal timing can vary from age 10 to 16 ½ .
Influences on and Effects of Timing of Puberty
There has been a lot of study on the onset of puberty for females. The major concern is whether or not going through puberty at a different time than others of the same age is good. The studies all point toward the same outcome that early onset of puberty for girls can be psychologically damaging. According to Marissa Sharum(mcs137@psu.edu), many females who start puberty early tend to view their body negatively. This could be do to the social pressures that force women to want to be thin. A girl who has gone through puberty early tends to be bigger and fatter than a girl who has not gone through puberty. This girl will stand out in comparison to the rest of her friends and will usually have a low self esteem. These females are usually rejected by their peers. Instead of looking for different friends within the same age group, they tend to make older and more mature friends. This can be bad for the less experienced and mentally immature individual. Hanging out with the older crowd can lead a teen into premature sex, and drug experiences. Ge et al. (1996) has theorized that these females may not have had enough time to complete the necessary childhood developmental tasks before entering the world of the older crowd. They have had less time to form a sense of self, which could lead them in making bad decisions for themselves as well as for the future. Another study by Simmons and Blyth (1987) also say that body image is the main focus on the early onset of puberty. Early developers are usually less satisfied with their body and are more likely to care about how they look at an early age. The main reason for their dissatisfaction is the fact that they weigh more than others. According to the study, when puberty becomes constant early developers still remain concerned about their body image. This is could be due to the change in the way they think. Early developers have learned to be insecure about themselves and although others have caught up with them physically, it is hard to change a trained mind. For males
Unlike girls, early development of puberty is not harmful for boys. There is not as much study done on boys as much as there is on girls. But one thing is agreeable, early onset among boys can be perceived as a head start. In most cultures, athleticism and strength is the main attraction for men. Knowing this, it could be concluded that a boy with more muscle tone and agility would be praised by other boys who has not passed puberty. This is what happens when a boy develops earlier. The boy is considered stronger and better than the rest of his peers. Other adolescence look up to him and his self esteem remains unharmed. According to Simmons and Blyth (1987), body image plays a huge role in male adolescence also. their study showed that early developers are satisfied with their height and body image. Early developers are happier and even after height and weight is controlled, they seem to be happier. In grade seven earlier developers considered themselves to be better looking, and in grade ten they considered themselves to be better in athletics. The study concluded that they have undoubtedly a head start in athletics. Addressing a college student that I knew went through puberty late (at about eleventh grade), he told me that he never got to play all the sports that he wanted to play. He said he felt he was not good enough and he was physically unable to play physical sports. Right now he is the best nonpaying athlete in his group of friends. He agrees that he can play sports good now but he still seems to be insecure about how good he is. Being a late developing boy can have its consequences. Late Bloomers can be frustrated when their friends are getting bigger and stronger. This sight talks about the different burdens that late developers go through and the damages that can be caused. With the competition that goes around as an athlete, the urge to be stronger is strong itself. Boys who's bodies are not ready for weightlifting are trying twice as hard to lift weights and exercise in order to keep up with the rest of his peers and competitors. This can be damaging to bones and muscles. Being less developed will cause peers to look down on a person. This person might feel incompetent in comparison to friends. Due to less developed muscles and height, a undeveloped boy will have a smaller chance of being good at sports. Remember that sports is a big issue in most cultures also.
Genetic—hereditary
Emotional—family conflict
Physical--

Adolescence Brain
Most Scientist believe that the brain was fully mature by puberty. Now, imaging studies reveal that the adolescence brain is still a work in progress. Dramatic changes in brain structures involved in emotions, judgment, organization of behavior, and self- control take place between puberty and young adulthood.