Girls are growing up too fast.

It’s a sentiment we hear so often, it is taken for granted to be true.

People point to revealing clothing marketed to little girls and media images that sexualize them. But there is another factor at work forcing some girls to grow up, perhaps faster than they would like: their own bodies.

Girls are going through puberty at an earlier age than they did a few decades ago.

While the age of a girl’s first period hasn’t changed too much in recent times, the age at which girls’ bodies mature has shifted significantly. At age 7, 10 percent of white girls, 15 percent of Hispanic girls and 23 percent black girls showed signs of breast development in a wide-scale study published in the journal Pediatrics in 2010. By age 8, breast development was seen in 18 percent of white girls, 31 percent of Hispanic girls and 43 percent of black girls. That is a significant increase, in particular for white girls. A study conducted in 1997 showed 6.7 percent of 7-year-old white girls developing breasts.

Scientists aren’t certain why girls are developing earlier, although there are plenty of theories (see “Potential causes”).

When girls develop early, it can have an impact on their lives. Girls who go through puberty at an early age are more likely to engage in risky behaviors, according to numerous academic studies.

A parent’s role can be crucial in determining just how well their daughter handles these confusing changes. But figuring out how to talk to kids about puberty, their changing bodies and sex can be difficult and awkward for some parents.

“I think everything is happening at a younger age. Some adults aren’t realizing that,” said local mom Tami Chapin, who has seen early changes in her kids. “I’m just shocked it happened so soon.”

Chapin remembers being excited to start her period when she entered ninth grade. Now she thinks girls starting puberty are too young, and they feel more burden than excitement. “I’m kind of sad for them that they are going to have to go through it so young.”

Dr. Cora Breuner, professor of pediatrics at the University of Washington School of Medicine, says many parents are worried about this topic and “don’t know how to talk about it with their kids.”

But she strongly encourages parents to be open with their children: “It is imperative for kids to get their information from their parents and not from the Internet. It normalizes it.”

What we know

Puberty is the process of our body transitioning from childhood to adulthood and becoming capable of sexual reproduction. Changes in the brain signal the ovaries and testes to produce hormones, which in turn transform the bones, skin, hair, breasts, sexual organs and brain. Puberty is complete when these changes have taken place.

Precocious puberty is when a child experiences puberty before age 8 — affecting about 1 in 160 kids. Age 8 and older is considered in the normal range for puberty to begin. But for many parents, the idea of an 8- or 9-year-old girl developing breasts, pubic hair and a period is unsettling, if not alarming.

The age of onset of menstruation changed significantly between the early 1800s, when girls started around age 15 or 16 in the U.S., and the 1950s. Since then, the average age a girl begins her period has remained relatively stable at around 12.4 years, according to research from Pediatrics in 2006. The average age is a little younger for girls who are black (12 years) or Hispanic (12.25 years).

The underlying reason for the shift in when menstruation starts is increased availability of food and resources, which explains why some developing nations still see girls starting their periods at a later age. In Haiti, for example, the age at which a girl starts menstruating is 15.4 years on average, according to the study.

Meanwhile, the age at which U.S. girls experience other changes has rapidly decreased. According to research from the Breast Cancer Fund, girls are now getting breasts one to two years earlier than they did 40 years ago.

The onset of puberty in boys does not appear to have shifted much.

Dr. Robert Epstein, author of “Teen 2.0: Saving our Children and Families from the Torment of Adolescence,” doesn’t want parents to become overly concerned about these changes: “The main thing I would say is, ‘Not to panic.’ ”

Even though puberty is inching earlier, there have always been young people who developed early. Parents and kids who are in this situation need to figure out the best way to navigate it.

Why it matters

Early menstruation or breast development isn’t just a matter of awkwardness, it’s associated with outcomes including an increased risk of developing breast cancer, according to the Breast Cancer Fund.

Researchers from the University of Melbourne found that teens who went through puberty early had a larger pituitary gland than their peers, and were more likely to experience depression and anxiety. A 2005 study in Pediatrics linked early puberty in girls with earlier use of alcohol and sexual activity, and also with increased risk of teen pregnancy. In 2004, a study in Pediatrics found “early maturers” (both boys and girls) were more likely to use drugs. Other academic studies have found early puberty linked with low self-esteem, smoking and more.

There are also social problems.

“Sometimes a person (who develops early) is stigmatized, ridiculed,” Epstein said. “Being different is problematic (for kids.)”

There are other consequences, as well. Girls who go through puberty tend to stop growing once they stop puberty. This means those who develop early are not as tall as their peers. Girls begin using up their eggs as soon as their periods start. There is speculation this could lead to reduced fertility in later years, according to recent research from Oregon State University.

How girls feel

Some kids resist going through puberty, said Epstein. They don’t want to become a different person from the one they are now.

Tami Chapin’s stepdaughter Delaney, a fifth-grader in Bend, just turned 11. At her birthday party, she and few friends talked about what going through puberty feels like.

One girl started going through puberty in fourth grade. “I told my mom my chest was hurting. I was like ‘What’s going on?’ ” she said. “She just thought that I was grumpy and nothing was happening.” A doctor’s visit later confirmed she was developing breasts. She felt like she was alone and no one else was going through the same thing. “I didn’t want to grow up; I want to still be little.”

None of the girls looked forward to the changes. And most of the girls who had bras didn’t like to wear them.

“It’s gross. I still refuse to wear a bra,” said one girl, who said her mom gave her bras for Christmas. “I just don’t want to face the fact that it’s happening. It means you’re growing up. It’s weird for me.”

Most of the girls also said that talking to their parents about the changes is hard, especially because most of the parents still want to see them as little girls.

“I think they forget how embarrassed they were,” said one girl.

Delaney said her mom still thinks she believes in the Tooth Fairy, so talking about puberty feels weird. She says she wants to know about what is going to happen, but that it’s also “kind of scary.”

“Your parent doesn’t want you growing up,” said another girl. When it comes to her dad, she said, he likes to call her “Love bug”: “I’m just like his little girl. Sometimes that’s a special thing, sometimes it’s annoying or babyish.”

Parental response

Parents can be caught off guard by puberty.

When should parents talk about it? With girls, a good rule of thumb is to make sure to cover all the details of puberty as soon as a girl begins to develop breasts, according to the American Academy of Pediatrics. Talks should include information about how a menstrual cycle works, cramps, hygiene and supplies.

Once kids hit age 8 or 9, Breuner said, parents need to open up because even if their own child is not developing, the child’s friend or sibling may be.

That said, she recognizes that the conversation isn’t going to be easy. “We have to be really comfortable with the fact that we are uncomfortable,” said Breuner.

“As a mom, the last thing you want to do is sit down and talk about birth control, what type of deodorant to wear or how to shave. It’s not as rewarding as when your kid takes a first step … this is hard stuff.”

Breuner said parents should also be prepared for the talk to be thanklessly received. “You don’t get a lot of instant gratification and the kids aren’t going to be nice back.” Instead of, “Thank you so much,” they will say “Ew! Why are you talking to me?” said Breuner. Expect kids to be squirming in their seats — but go ahead anyway, she said.

Chapin says talking with her kids is something she and her husband feel is necessary. “It’s not bad, it’s not taboo — it’s life, it’s natural.”

Epstein encourages parents to respond to each child differently — some kids who develop early will do so without much strife. He believes parents should view signs of puberty as signs of adulthood and encourage kids to cherish that move forward.

Parents who aren’t sure how to respond to a child’s changing appearance may offer jokes or friendly jabs. The American Academy of Pediatrics cautions against this approach, even if intended to be good natured, saying, “Respect the fact that teens are often highly self-conscious about their ‘new parts.’ ”

For girls who are developing early, Breuner suggests asking them questions: How do you feel about this? How can I help you navigate this? Remind them that their friends will catch up; it just takes time. Breuner also encourages parents to talk about what to do if they are put in a “situation of intimacy that gets farther than you want.” Parents likely won’t want to think about this — and kids may say “ew” — but Breuner believes addressing the issue isn’t going to hurt. “No data shows talking about this pushes a girl into being more sexually active earlier or alienates the child.”

She encourages parents to acknowledge they feel uncomfortable, but to continue. Breuner likes the resources and talking points available through the American Academy of Pediatrics website — “you don’t have to reinvent the wheel,” she said.

The key is to be engaged, supportive and to try your best to remember what it felt like to be 11 and you wanted more than anything to fit in.

By the numbers

18%

of 8-year-old white girls show signs of breast development.

43%

of 8-year-old black girls show signs of breast development.

15-16

is the average age at which a girl started menstruating in the early 1800s.

12.4

is the average age at which a girl starts menstruating today.

Pediatrics, the journal of the American Academy of Pediatrics

Potential causes

There are many theories as to why puberty is inching earlier for girls, in particular. Some are speculative and none are conclusive. The following is a summary of the leading theories and research about the potential causes of early puberty:

• Obesity

Girls with higher body mass indexes tend to go through puberty at a younger age than other girls, according to numerous ongoing studies. In many ways, this can explain why the age has lowered during the past few centuries, as food has become more abundant. Writing in the Huffington Post, Dr. Joel Fuhrman said, “Excess body fat alters the levels of the hormones insulin, leptin, and estrogen,” which are believed to be linked to the onset of puberty. He also linked the intake of more animal protein with an earlier start of puberty.

• Chemicals/ hormones/BPA

Chemicals and hormones can be found in many products and speculation is strong about their connection to early puberty. The American Academy of Pediatrics offers this: “Believe it or not, the use of hair creams, makeup and other cosmetic products containing estrogen can spur” pseudoprecocious puberty, in which high levels of sex hormones are activated. Many people point to hormones given to animals used for meat and dairy products, believing these hormones are part of the problem. Many people are also concerned about bisphenol-A, known as BPA, found in many products made of hard plastic. BPA is a known endocrine disrupter. According to the National Institutes for Health, endocrine disrupters are “chemicals that may interfere with the body’s endocrine system and produce adverse developmental, reproductive, neurological, and immune effects in both humans and wildlife.”

• Attachment

Researchers found a link between the attachment of babies with their mothers and the timing of puberty, based on a study involving 373 children followed from birth to age 15 published in 2010 in Psychological Science. The girls with less strong attachment were more likely to have their first period before the girls who showed strong attachment to their mothers as babies. There is an evolutionary theory as to why this would occur — girls who live in a more unstable environment would mature more quickly to hasten their ability to find a more stable environment and reproduce before they die, according to the researchers.

• Family structure and stress

Girls who experience harsh family environments are more likely to start puberty early, according to research from 2007 in the Child Development journal. This development is also believed to be linked to evolutionary causes. The idea being that the body receives a message that there aren’t males around, the environment is unstable and therefore the girls mature more quickly. Having a stable and supportive stepfather, however, seems to slow the onset of puberty.

— Alandra Johnson, The Bulletin