The Start of Puberty

Young plant
Picture of young plant shooting up.

Puberty is happening to humans younger than it has at any other moment in history. Over the past 150 years, scientists have noticed a secular trend, where the age of puberty lowers by 2-4 months per generation. It is a very robust effect, noted in girls and boys, and across many different samples. This trend is attributed to access to better nutrition and health, obesity, and exposure to pseudo estrogens in cosmetics, food, and the environment. While the secular trend appears to be slowing down, time will tell if the trend completely flattens out.

When puberty starts for one person compared to another the cumulation of a wide range of factors, including genetics, family factors, nutrition, and health. Understanding this can help you estimate when your child will go through puberty. This is useful information because surprises are almost never a good thing when parenting. Prepared parenting means that you can have realistic conversations with your kids about their bodies long before their bodies start changing.


Genetics from biological mom and dad create the window when puberty is likely to occur for a child. For example, the best indicator of when a girl will start her period is the age at which her biological mother started her period. Remember, that menstruation is one of the last steps in pubertal maturation for girls (learn more about that here), meaning that when women remember getting their period, they are remembering the end of the process of puberty; puberty actually began years earlier. So, when the biological mother started menstruating, minus 2-5 years, is the likely window of when a girl will start puberty.

For boys, the same is true: the age of when the biological father went through puberty is a strong predictor of when the child will go through puberty. Remember, the outward signs of puberty for boys, like voice change and facial hair, are at the end of the pubertal process (learn more here). So just like girls, subtracting 2-5 years from when the biological dad first achieved these milestones will give you an idea of when puberty is going to begin. 

Environment still matters though. Genetics inform the general window of time when puberty will start and how fast a child will go through the process of puberty – but environmental factors will determine when everything happens within that window. 

(The tempo of puberty – how fast boys and girls move through it – is not well understood but seems to be primarily influenced by genetics.)​

Environmental Factors

Many environmental factors influence the timing of puberty.

Most people are surprised when I tell them that the family environment and life circumstances of a child affect the timing puberty. Among girls, greater conflict at home or having been physically or sexually abused in childhood are linked with earlier maturation. As an instructor of psychology, I have terrified upward of 2,000 students over the years with this one, creepy, fact: girls who live with a stepfather will start puberty early due the presence of a sexually mature, non-related male in the environment. (It’s hypothesized that pheromones trigger this process. There is no documented association of this effect for boys. Stepmothers may now let out a sigh of relief.) Evidence that family factors affect the timing of male puberty are too weak and inconsistent to be of note.

Evidence is mounting that hormone disrupter chemicals, such as BPA, parabens, phthalates found in our plastics, cosmetics, and food impact the timing of puberty. However, it’s not well understood if these hormones accelerate or decelerate the timing of puberty. For example, exposure to these chemicals is associated with later puberty for boys. Among girls, some of these chemicals are associated with earlier puberty, and others are associated with later puberty. In other words, exposure to pseudo-estrogens that affect the hormones of our body influence puberty and reproductive systems. But we still don’t understand the extent to which it is happening and what might make some kids more vulnerable than others to the effects of these chemicals. So, while I cannot provide a quick synopsis of how and why this happens – we are truly still learning – some scientists have argued it makes precautionary sense to avoid these endocrine disrupter hormones as much as possible.

While all these factors contribute, at the biological level, one event seems to be associated with the puberty trigger: the presence of sufficient body fat. At the biological level, fat cells produce a protein called leptin. Rising levels of leptin, from rising levels of fat, instruct the hypothalamus to open the gate to puberty. This may explain why obesity is correlated with the secular trend: as people have gained more weight at younger ages, puberty has shifted lower. Indeed, stress, nutritional deficiencies and excessive exercise can all delay puberty, possibly because they are associated with lower body fat. Regardless, an increase in body fat that is observed in many pre-teens is a near slam dunk in identifying that puberty is near.

In some ways, this article is a bit of a “no shit” on the timing puberty. Oh, genetics and environment matter? No shit.

But let me be clear. This shit matters.

First, it is empowering for your child to understand why puberty is happening to them and when they can expect it. Not only is it good for you to prepare yourself, it’s good for them to be ready for a big change. Talking to your child about your experience and timing of puberty are a great way to help prepare them.

Second, it is good for a child to understand that they have a genetic set of cards, but that the choices they make with their body can affect their lives. We are not always slaves to our genetics. The choices we make with nutrition, health, and attitude can have real implications about how we feel about ourselves.

Empower your child to view puberty positively. It’s a huge gift you can give to them.

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