- Puberty is the period of sexual maturation and achievement of fertility.
- The time when puberty begins varies greatly among individuals; however, puberty usually occurs in girls between the ages of 10 and 14 and between the ages of 12 and 16 in boys.
- Both genetic and environmental factors are involved in the timing of puberty.
- Body fat and/or body composition may play a role in regulating the onset of puberty.
- Puberty is associated with the development of secondary sex characteristics and rapid growth.
- Central precocious puberty (CPP) is puberty that occurs earlier than normal due to release of hormones from the hypothalamus of the brain.
- Girls are more likely than boys to have precocious puberty.
- Puberty may also be accompanied by emotional and mood changes.
- Some medical conditions may worsen or first become apparent at puberty.
What is puberty?
Puberty is the period during which growing boys or girls undergo the process of sexual maturation. Puberty involves a series of physical stages or steps that lead to the achievement of fertility and the development of the so-called secondary sex characteristics, the physical features associated with adult males and females (such as the growth of pubic hair). While puberty involves a series of biological or physical transformations, the process can also have an effect on the psychosocial and emotional development of the adolescent.
When does puberty occur?
The onset of puberty varies among individuals. Puberty usually occurs in girls between the ages of 10 and 14, while in boys it generally occurs later, between the ages of 12 and 16. In some African-American girls, puberty begins earlier, at about age 9, meaning that puberty occurs from ages 9 to 14.
Adolescent girls reach puberty today at earlier ages than were ever recorded previously. Nutritional and other environmental influences may be responsible for this change. For example, the average age of the onset of menstrual periods in girls was 15 in 1900. By the 1990s, this average had dropped to 12 and a half years of age.
Signs and Symptoms of Central Precocious Puberty
"Secondary sex changes" are those physical changes associated with the progressive rise in sex hormones -- estrogen and progesterone in females and testosterone in males. Such secondary sex changes include
- breast tissue development,
- enlargement of the testes (testicles) and penis, and
- presence of pubic hair, axillary hair, and facial hair.
Other developmental changes include
- initiation of menstrual periods,
- increasing in sweat production,
- development of body odor,
- lowering of the pitch of voice, rapid height acquisition ("growth spurt"), and
- increase in size and strength of muscles.
What determines when puberty begins?
The timing of the onset of puberty is not completely understood and is likely determined by a number of factors. One theory proposes that reaching a critical weight or body composition may play a role in the onset of puberty. It has been proposed that the increase in childhood obesity may be related to the overall earlier onset of puberty in the general population in recent years.
Leptin, a hormone produced by fat cells (adipocytes) in the body, has been suggested as one possible mediator of the timing of puberty. In research studies, animals deficient in leptin did not undergo puberty, but puberty began when leptin was administered to the animals. Further, girls with higher concentrations of the hormone leptin are known to have an increased percentage of body fat and an earlier onset of puberty than girls with lower levels of leptin. The concentration of leptin in the blood is known to increase just before puberty in both boys and girls.
Leptin, however, is likely only one of multiple influences on the hypothalamus, an area of the brain that releases a hormone known as gonadotropin-releasing hormone (GnRH), which in turn signals the pituitary gland to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH and FSH secretion by the pituitary is responsible for sexual development.
Genetic factors are likely involved in the timing of puberty, and the timing of puberty has often been described to "run in families." Additionally, a gene has been identified that appears to be critical for the normal development of puberty. The gene, known as GPR54, encodes a protein that appears to have an effect on the secretion of GnRH by the hypothalamus. Individuals who do not have a functioning copy of this gene are not able to enter puberty normally.
What are the physical stages of puberty in girls and boys?
The changes that happen during the process of puberty have a typical pattern in both boys and girls, with a generally predictable sequence of events. In most girls, the first sign of puberty is the beginning of breast development (breast buds), which occurs at an average age of approximately 11 years. In girls, the growth of pubic hair typically begins next, followed by the growth of hair in the armpits. A minority of girls, however, begin to develop pubic hair prior to breast development. The onset of menstruation (having periods) usually happens later than the other physical changes and usually occurs around two and a half years after the onset of puberty.
A regular pattern of ovulation, corresponding to achievement of fertility, usually develops rapidly once a girl begins having menstrual periods. However, girls who have a later onset of menstruation (after age 13) tend to have lower rates of regular ovulation in the years following the onset of menstruation. Studies have shown that one-half of adolescent girls who first begin to menstruate after age 13 will not ovulate regularly over the next four and a half years.
In boys, an increase in the size of the testicles is the first change observed at the onset of puberty. Enlargement of the testicles begins at an approximate average age of 11 and a half years in boys and lasts for about six months. After enlargement of the testicles, the penis also increases in size. Enlargement of the testicles and penis almost always occurs before the development of pubic hair. The next stage is the growth of pubic hair and hair in the armpits. Next, the voice becomes deeper and muscles increase in size. The last step is usually the development of facial hair.
Fertility is achieved in males near the onset of puberty, when a surge in testosterone triggers the production of sperm.
The sequence of changes in puberty has been characterized by physicians and is referred to as sexual maturity rating (SMR) or Tanner stages, named after a physician who published a description of the sequence of physical changes in puberty in 1969. Tanner stages are determined by the development of the secondary sex characteristics and encompass changes in the size and appearance of the external genitalia, the development of pubic hair, and breast development in girls. Tanner stages allow doctors to classify the extent of development of sex characteristics into five distinct steps ranging from stage 1 (prepubertal) to stage 5 (mature adult type).
What other changes in the body occur during puberty in boys and girls?
The "growth spurt"
A rapid increase in height, referred to as a growth spurt, usually accompanies puberty. This rapid increase in height typically lasts for two to three years. About 17%-18% of adult height is attained during puberty. Although the increase in height affects both the trunk and the limbs, growth in the limbs usually happens first. The growth spurt characteristically occurs earlier in girls than in boys, with girls having the growth spurt approximately two years prior to boys, on average. In girls, the growth spurt typically precedes the onset of menstruation by about six months.
Bone growth and mineralization
Puberty is accompanied by growth of bones and increases in bone density in both boys and girls. In girls, bone mineralization peaks around the time of the onset of menstrual periods, after the time of peak height velocity (growth spurt). Studies have shown that bone width increases first, followed by bone mineral content, and lastly by bone density. Because of the lag between bone growth and achievement of full bone density, adolescents may be at increased risk for fractures during this time.
Changes in weight and body composition occur in both boys and girls. Adolescent girls develop a greater proportion of body fat than boys, with redistribution of the fat toward the upper and lower portions of the body, leading to a curvier appearance. While boys also have an increase in the growth of body fat, their muscle growth is faster. By the end of puberty, boys have a muscle mass about one and a half times greater than that of comparably sized girls.
Maturation of the cardiovascular systems and lungs results in an increased working capacity of these organs, associated with an overall increase in endurance and strength. These changes are more pronounced in boys than in girls.
What emotional changes occur in puberty in boys and girls?
Both boys and girls can experience emotional changes that accompany the myriad physical changes of puberty. These changes are not the same for all adolescents. Changes can occur in the way a teen responds to family or friends and views him- or herself. Many adolescents experience mood swings, anxiety, confusion, and sensitivity. On the other hand, not all emotional changes of puberty are related to negative thoughts or feeling upset. Puberty is also a time in which the young person learns about his or her own interests and goals and learns to relate to others in a more mature way. While some emotional changes are a normal part of puberty, it is important to seek medical help if these emotional changes are unusually severe, affect day-to-day functioning, or result in thoughts of harming oneself or others.
What are the medical concerns associated with normal puberty?
While puberty is a normal condition and not an illness, many medical conditions and illnesses may first appear during puberty. Some conditions potentially associated with puberty include the following:
- Acne: Acne is an inflammation of the sebaceous glands and hair follicles of the skin, which is most pronounced on the face but may occur on the neck, back, chest, or other areas. The hormonal changes in puberty lead to the development of acne in many adolescent boys and girls.
- Gynecomastia: Gynecomastia is the term used to describe enlargement of the male breasts. The hormonal changes of puberty can cause a transient gynecomastia in normal boys that typically lasts for six to 18 months. Pubertal gynecomastia occurs at an average age of 13 in boys and affects up to one-half of normal adolescent boys.
- Anemia: The normal pubertal progression in males is associated with increases in the ferritin (iron) and hemoglobin concentrations in the blood, but this increase is not observed in females. Adolescent girls tend to consume less iron-containing foods than boys, and this, combined with blood losses through menstrual bleeding, may place adolescent girls at risk for anemia.
- Sexually transmitted diseases (STDs): If teens become sexually active at puberty, they are at risk for HIV and other sexually transmitted infections.
- Scoliosis: Because of rapid growth during puberty, scoliosis (abnormal curvature of the spine) can be worsened or may first become apparent during puberty.
- Vision changes: Nearsightedness (myopia) has a high incidence during puberty because of growth in the axial diameter of the eye.
- Musculoskeletal injuries: Adolescents may be particularly prone to musculoskeletal injuries during the growth spurt and during growth of muscle mass. Since bone growth usually precedes full bone mineralization, adolescents are at risk for fractures. Also, since the growth in the limbs usually occurs prior to growth in the trunk, some joints may be left with a limited range of motion that increases the risk for sprains and strains.
- Dysfunctional uterine bleeding: Girls who have recently begun menstruating may have irregular, prolonged, or heavy menstrual bleeding. Anovulation (not ovulating) is the most common reason for abnormal menstrual bleeding in adolescent girls.
What are medical conditions associated with early or late puberty?
Precocious puberty is the medical term for puberty that occurs earlier than usual. This is sometimes referred to as central precocious puberty or CPP when it is due to the brain releasing hormones that control puberty at an earlier age than normal. While medical professionals are not in full agreement about the age ranges for the definition of precocious puberty, many doctors believe that a medical evaluation for precocious puberty should be performed if the signs and symptoms of puberty (breast or pubic hair development) occur prior to age 7 in Caucasian girls and prior to age 6 in African-American girls. Boys who show signs of developing secondary sex characteristics prior to age 9 are also considered to have precocious puberty. Precocious puberty can be associated with psychological difficulties that may impact a child's emotional development.
Precocious puberty is much more common in girls than in boys. Many girls experience precocious puberty in the absence of any disease or condition. In boys, however, precocious puberty is more likely to be associated with an underlying medical problem. While in many cases the exact cause of precocious puberty cannot be determined, a small number of cases are related to abnormalities of the ovaries or testes, thyroid gland abnormalities or other hormone problems, genetic conditions, tumors or infections of the brain, and injury to the brain.
Precocious puberty may be treated by treating the underlying condition that is responsible for the condition or by lowering the high levels of sex hormones with medications (known as GnRH agonists) that block the production of sex hormones to stop sexual development from progressing.
Delayed puberty is the late onset of puberty. Puberty is usually considered to be delayed when there has been no increase in testicular volume by 14 years of age in boys and no breast development by 13 and a half years of age in girls. Sometimes, delayed puberty tends to "run in families," and normal adolescent development proceeds normally after the delay. This is sometimes called a constitutional delay and is responsible for the vast majority of cases of delayed puberty. Constitutional delay that affects both growth and achievement of puberty is much more common in boys than in girls.
Chronic medical conditions, such as diabetes or cystic fibrosis, may also cause the delayed onset of puberty. Genetic conditions, problems with the pituitary or thyroid glands, problems with the ovaries or testes, and malnutrition are other causes of delayed puberty. Many girls who exercise strenuously have very little body fat and also experience a delay in the onset of puberty, since a certain amount of body fat appears to be required for the initiation of puberty. Girls who are competitive athletes may have a delay in the onset of menstruation of up to one year or more when compared with nonathletes.
Medically Reviewed on 9/1/2016
American Academy of Pediatrics. <http://www.healthychildren.org/English/ages-stages/gradeschool/puberty/Pages/default.aspx>.
Kaplowitz, Paul B. "Precocious Puberty." Medscape.com. June 24, 2016. <http://emedicine.medscape.com/article/924002-overview>.